hemx/hemx-build/src/lib.rs

use hemplate_core::ast::build_ast;
use hemplate_core::surface::{
    extract_surface, AttributeOrigin, ControlKind, ScopeId, ScopeKind, SurfaceAttribute,
    SurfaceDocument, SurfaceNodeKind,
};
use hemx_core::{EFFECT_BATCH_ABI_VERSION, RUNTIME_ABI_VERSION, SURFACE_SCHEMA_VERSION};
use std::collections::{BTreeMap, BTreeSet};
use std::io;
use std::path::{Path, PathBuf};
use std::sync::Arc;

#[derive(Clone, Debug)]
pub struct AppBuilder {
    out_dir: Option<PathBuf>,
    template_dir: PathBuf,
    global_exports: bool,
    surfaces: Vec<(PathBuf, SurfaceDocument)>,
}

impl AppBuilder {
    pub fn out_dir(mut self, out_dir: impl Into<PathBuf>) -> Self {
        self.out_dir = Some(out_dir.into());
        self
    }

    pub fn template_dir(mut self, template_dir: impl Into<PathBuf>) -> Self {
        self.template_dir = template_dir.into();
        self
    }

    pub fn global_exports(mut self, enabled: bool) -> Self {
        self.global_exports = enabled;
        self
    }

    pub fn surface(mut self, path: impl Into<PathBuf>, surface: SurfaceDocument) -> Self {
        self.surfaces.push((path.into(), surface));
        self
    }

    pub fn run(self) -> io::Result<()> {
        println!("cargo:rerun-if-changed={}", self.template_dir.display());

        let out_dir = self
            .out_dir
            .or_else(|| std::env::var_os("OUT_DIR").map(PathBuf::from));

        let Some(out_dir) = out_dir else {
            return Ok(());
        };

        std::fs::create_dir_all(&out_dir)?;

        let mut resources = Resources::default();
        if self.surfaces.is_empty() {
            for path in collect_heml(&self.template_dir)? {
                let source = std::fs::read_to_string(&path)?;
                let doc = build_ast(Arc::new(source)).map_err(|err| parse_error(&path, err))?;
                let Some(doc) = doc else {
                    continue;
                };
                let surface = extract_surface(&doc);
                resources.add_surface(&self.template_dir, &path, &surface)?;
            }
        } else {
            // req: surface/008
            for (path, surface) in &self.surfaces {
                resources.add_surface(&self.template_dir, path, surface)?;
            }
        }
        for path in collect_stylesheets(&self.template_dir)? {
            let source = std::fs::read_to_string(&path)?;
            resources.add_stylesheet(&self.template_dir, &path, &source)?;
        }

        std::fs::write(
            out_dir.join("hemx.generated.rs"),
            resources.generated_rs(self.global_exports),
        )?;
        std::fs::write(out_dir.join("hemx.syms"), resources.syms())?;
        Ok(())
    }
}

pub fn app() -> AppBuilder {
    AppBuilder {
        out_dir: None,
        template_dir: PathBuf::from("templates"),
        global_exports: false,
        surfaces: Vec::new(),
    }
}

#[derive(Default)]
struct Resources {
    slots: BTreeMap<String, Resource>,
    handles: BTreeMap<String, Resource>,
    handle_forms: BTreeMap<String, String>,
    handle_params: BTreeMap<String, BTreeSet<String>>,
    forms: BTreeMap<String, FormResource>,
    atoms: BTreeMap<String, Resource>,
    classes: BTreeMap<String, ClassToken>,
    events: BTreeMap<String, EventToken>,
}

#[derive(Clone, Debug)]
struct Resource {
    symbol: String,
    ident: String,
    component: String,
    keyed: bool,
    id: u32,
}

#[derive(Clone, Debug)]
struct FormResource {
    resource: Resource,
    controls: Vec<GeneratedControl>,
}

#[derive(Clone, Debug)]
struct GeneratedControl {
    name: String,
    kind: ControlKind,
    required: bool,
}

#[derive(Clone, Debug)]
struct ClassToken {
    symbol: String,
    ident: String,
    component: String,
    token: String,
}

#[derive(Clone, Debug)]
struct EventToken {
    symbol: String,
    ident: String,
    component: String,
    name: String,
}

impl Resources {
    fn add_surface(
        &mut self,
        root: &Path,
        path: &Path,
        surface: &SurfaceDocument,
    ) -> io::Result<()> {
        let component = component_ident(root, path)?;
        for node in &surface.nodes {
            let SurfaceNodeKind::Element { tag } = &node.kind else {
                continue;
            };

            reject_selector_target_attrs(path, &node.attrs)?;
            reject_unknown_hemx_attrs(path, &node.attrs)?;
            reject_invalid_hemx_attr_values(path, &node.attrs)?;
            reject_invalid_hemx_attr_placement(path, tag, &node.attrs)?;

            if let Some(class_attr) = static_attr(&node.attrs, "class") {
                for token in class_tokens(&class_attr) {
                    let canonical = canonical_symbol(root, path, token);
                    self.insert_class(canonical, token.to_owned(), component.clone())?;
                }
            }

            if let Some(on_attr) = static_attr(&node.attrs, "data-hemx-on") {
                for event in event_tokens(&on_attr) {
                    let canonical = canonical_symbol(root, path, event);
                    self.insert_event(canonical, event.to_owned(), component.clone())?;
                }
            }

            if let Some(name) = static_attr(&node.attrs, "data-hemx-slot") {
                reject_unkeyed_loop(surface, node.scope, path, "slot", &name)?;
                let keyed = is_inside_keyed_for(surface, node.scope)
                    || (can_host_keyed_collection(tag)
                        && has_descendant_keyed_for_scope(surface, node.scope));
                let canonical = canonical_symbol(root, path, &name);
                self.insert_slot(canonical, name, component.clone(), keyed)?;
            }

            if let Some(name) = static_attr(&node.attrs, "data-hemx-atom") {
                reject_unkeyed_loop(surface, node.scope, path, "atom", &name)?;
                let canonical = canonical_symbol(root, path, &name);
                self.insert_atom(canonical, name, component.clone())?;
            }

            if let Some(name) = static_attr(&node.attrs, "data-hemx-handle") {
                reject_unkeyed_loop(surface, node.scope, path, "handle", &name)?;
                let canonical = canonical_symbol(root, path, &name);
                self.insert_handle(canonical, name.clone(), component.clone())?;
                self.insert_handle_params(&name, &node.attrs)?;

                if tag == "form" {
                    let form_name =
                        static_attr(&node.attrs, "data-hemx-form").unwrap_or_else(|| name.clone());
                    let controls = surface
                        .forms
                        .iter()
                        .find(|form| form.node == node.id)
                        .map(|form| {
                            form.controls
                                .iter()
                                .map(|control| GeneratedControl {
                                    name: control.name.clone(),
                                    kind: control.kind.clone(),
                                    required: control.required,
                                })
                                .collect()
                        })
                        .unwrap_or_default();
                    self.insert_form(
                        canonical_symbol(root, path, &form_name),
                        form_name.clone(),
                        component.clone(),
                        controls,
                    )?;
                    if let (Some(handle_ident), Some(form_ident)) =
                        (rust_ident(&name), rust_ident(&form_name))
                    {
                        self.handle_forms.insert(handle_ident, form_ident);
                    }
                }
            }
        }
        Ok(())
    }

    fn insert_slot(
        &mut self,
        symbol: String,
        name: String,
        component: String,
        keyed: bool,
    ) -> io::Result<()> {
        insert_resource(&mut self.slots, "slot", symbol, name, component, keyed)
    }

    fn insert_handle(&mut self, symbol: String, name: String, component: String) -> io::Result<()> {
        insert_resource(&mut self.handles, "handle", symbol, name, component, false)
    }

    fn insert_atom(&mut self, symbol: String, name: String, component: String) -> io::Result<()> {
        insert_resource(&mut self.atoms, "atom", symbol, name, component, false)
    }

    fn insert_class(&mut self, symbol: String, token: String, component: String) -> io::Result<()> {
        let ident = class_ident(&token).ok_or_else(|| {
            io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "invalid CSS class `{token}`; expected an ASCII class token usable from Rust"
                ),
            )
        })?;
        let class = ClassToken {
            symbol,
            ident,
            component,
            token,
        };
        if let Some(existing) = self
            .classes
            .values()
            .find(|existing| existing.ident == class.ident && existing.token != class.token)
        {
            return Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "duplicate generated class identifier `{}` for CSS classes `{}` and `{}`",
                    class.ident, existing.token, class.token
                ),
            ));
        }
        match self.classes.get(&class.symbol) {
            Some(existing) if existing.token != class.token => Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!("conflicting CSS class token for `{}`", existing.symbol),
            )),
            Some(_) => Ok(()),
            None => {
                self.classes.insert(class.symbol.clone(), class);
                Ok(())
            }
        }
    }

    fn insert_handle_params(&mut self, handle: &str, attrs: &[SurfaceAttribute]) -> io::Result<()> {
        let Some(handle_ident) = rust_ident(handle) else {
            return Ok(());
        };
        for attr in attrs {
            if !is_handle_param_attr(attr) {
                continue;
            }
            let Some(param) = data_param_ident(&attr.name) else {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidData,
                    format!("invalid handler param attribute `{}`; expected data-* name usable from Rust", attr.name),
                ));
            };
            self.handle_params
                .entry(handle_ident.clone())
                .or_default()
                .insert(param);
        }
        Ok(())
    }

    fn insert_event(&mut self, symbol: String, name: String, component: String) -> io::Result<()> {
        let ident = event_ident(&name).ok_or_else(|| {
            io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "invalid hemx event `{name}`; expected an ASCII event name usable from Rust"
                ),
            )
        })?;
        let event = EventToken {
            symbol,
            ident,
            component,
            name,
        };
        match self.events.get(&event.symbol) {
            Some(existing) if existing.name != event.name => Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!("conflicting event name for `{}`", existing.symbol),
            )),
            Some(_) => Ok(()),
            None => {
                self.events.insert(event.symbol.clone(), event);
                Ok(())
            }
        }
    }

    fn insert_form(
        &mut self,
        symbol: String,
        name: String,
        component: String,
        controls: Vec<GeneratedControl>,
    ) -> io::Result<()> {
        let controls = controls
            .into_iter()
            .filter(|control| control.name != "__h")
            .collect();
        let resource = make_resource("form", symbol, name, component, false)?;
        match self.forms.get(&resource.ident) {
            Some(existing) if existing.resource.symbol != resource.symbol => Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "duplicate generated identifier `{}` for `{}` and `{}`",
                    resource.ident, existing.resource.symbol, resource.symbol
                ),
            )),
            Some(_) => Ok(()),
            None => {
                self.forms
                    .insert(resource.ident.clone(), FormResource { resource, controls });
                Ok(())
            }
        }
    }

    fn add_stylesheet(&mut self, root: &Path, path: &Path, source: &str) -> io::Result<()> {
        let component = component_ident(root, path)?;
        for token in stylesheet_class_tokens(source) {
            let canonical = canonical_symbol(root, path, token);
            self.insert_class(canonical, token.to_owned(), component.clone())?;
        }
        Ok(())
    }

    fn generated_rs(&self, global_exports: bool) -> String {
        let mut out = String::new();
        out.push_str("// @generated by hemx-build. Do not edit.\n");
        out.push_str(&format!(
            "pub const BUILD_FINGERPRINT: ::hemx::advanced::BuildFingerprint = ::hemx::advanced::BuildFingerprint::from_parts(&[{}]);\n\n",
            self.fingerprint_parts()
                .into_iter()
                .map(|part| part.to_string())
                .collect::<Vec<_>>()
                .join(", ")
        ));

        // req: build/001 req: component/003
        if global_exports {
            self.push_component_refs(&mut out, 0);
            self.push_resource_modules(&mut out, None, 0);
        }
        self.push_lowering_api(&mut out, None, 0);

        for component in self.component_names() {
            out.push_str("\n#[allow(non_upper_case_globals)]\n");
            out.push_str(&format!("pub mod {component} {{\n"));
            self.push_resource_modules(&mut out, Some(&component), 1);
            self.push_lowering_api(&mut out, Some(&component), 1);
            out.push_str("}\n");
        }

        self.push_lowering_helpers(&mut out);
        out
    }

    fn push_component_refs(&self, out: &mut String, indent: usize) {
        let pad = "    ".repeat(indent);
        let inner = "    ".repeat(indent + 1);
        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod components {{\n"
        ));
        for component in self.component_names() {
            out.push_str(&format!(
                "{inner}pub const {component}: ::hemx::ComponentRef = ::hemx::ComponentRef::new({});\n",
                rust_str(&component)
            ));
        }
        out.push_str(&format!("{pad}}}\n"));
    }

    fn push_resource_modules(&self, out: &mut String, component: Option<&str>, indent: usize) {
        let pad = "    ".repeat(indent);
        let inner = "    ".repeat(indent + 1);
        let mut handle_ids = Vec::new();
        let mut root_exports = BTreeSet::new();

        if let Some(component) = component {
            out.push_str(&format!(
                "{pad}pub const COMPONENT: ::hemx::ComponentRef = ::hemx::ComponentRef::new({});\n",
                rust_str(component)
            ));
        }

        out.push_str(&format!("{pad}#[doc(hidden)]\n{pad}pub mod advanced {{\n"));
        out.push_str(&format!(
            "{inner}#[allow(non_upper_case_globals)]\n{inner}pub mod slots {{\n"
        ));
        let slot_inner = "    ".repeat(indent + 2);
        for res in self
            .slots
            .values()
            .filter(|res| component_matches(res, component))
        {
            if res.keyed {
                out.push_str(&format!(
                    "{slot_inner}pub const {}: ::hemx::advanced::KeyedSlot<::std::string::String, ::std::string::String> = ::hemx::advanced::KeyedSlot::new({});\n",
                    res.ident, res.id
                ));
            } else {
                out.push_str(&format!(
                    "{slot_inner}pub const {}: ::hemx::advanced::Slot<::std::string::String> = ::hemx::advanced::Slot::new({});\n",
                    res.ident, res.id
                ));
            }
        }
        out.push_str(&format!("{inner}}}\n"));
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod targets {{\n"
        ));
        out.push_str(&format!("{inner}#[derive(Clone, Copy)]\n"));
        out.push_str(&format!(
            "{inner}pub struct SlotTarget<T> {{ slot: ::hemx::advanced::Slot<T> }}\n"
        ));
        out.push_str(&format!("{inner}#[allow(dead_code)]\n"));
        out.push_str(&format!("{inner}impl<T> SlotTarget<T> {{\n"));
        out.push_str(&format!("{inner}    const fn new(slot: ::hemx::advanced::Slot<T>) -> Self {{ Self {{ slot }} }}\n"));
        out.push_str(&format!("{inner}    pub fn put(self, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect {{ super::put(self.slot, view) }}\n"));
        out.push_str(&format!("{inner}    pub fn replace(self, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect {{ super::put(self.slot, view) }}\n"));
        out.push_str(&format!("{inner}    pub fn text(self, value: impl ::std::string::ToString) -> ::hemx::advanced::Effect {{ self.slot.text(value) }}\n"));
        out.push_str(&format!("{inner}    pub fn set(self, value: impl ::std::string::ToString) -> ::hemx::advanced::Effect {{ self.slot.text(value) }}\n"));
        out.push_str(&format!("{inner}}}\n"));
        out.push_str(&format!(
            "{inner}impl<T> ::hemx::GeneratedTarget for SlotTarget<T> {{\n"
        ));
        out.push_str(&format!("{inner}    fn __hemx_resource_id(self) -> ::hemx::advanced::ResourceId {{ self.slot.id() }}\n"));
        out.push_str(&format!("{inner}}}\n"));
        out.push_str(&format!("{inner}#[derive(Clone, Copy)]\n"));
        out.push_str(&format!("{inner}pub struct KeyedSlotTarget<K, T> {{ slot: ::hemx::advanced::KeyedSlot<K, T> }}\n"));
        out.push_str(&format!("{inner}#[allow(dead_code)]\n"));
        out.push_str(&format!("{inner}impl<K, T> KeyedSlotTarget<K, T>\n"));
        out.push_str(&format!("{inner}where\n"));
        out.push_str(&format!("{inner}    K: ::std::string::ToString,\n"));
        out.push_str(&format!("{inner}{{\n"));
        out.push_str(&format!("{inner}    const fn new(slot: ::hemx::advanced::KeyedSlot<K, T>) -> Self {{ Self {{ slot }} }}\n"));
        out.push_str(&format!("{inner}}}\n"));
        out.push_str(&format!(
            "{inner}impl<T> KeyedSlotTarget<::std::string::String, T> {{\n"
        ));
        out.push_str(&format!("{inner}    pub fn append(self, view: impl ::hemplate::Hemplate + ::hemx::KeyedPartial) -> ::hemx::advanced::Effect {{ self.slot.append_html(view.hemx_key(), super::render(&view)) }}\n"));
        out.push_str(&format!("{inner}    pub fn prepend(self, view: impl ::hemplate::Hemplate + ::hemx::KeyedPartial) -> ::hemx::advanced::Effect {{ self.slot.prepend_html(view.hemx_key(), super::render(&view)) }}\n"));
        out.push_str(&format!("{inner}    pub fn replace(self, view: impl ::hemplate::Hemplate + ::hemx::KeyedPartial) -> ::hemx::advanced::Effect {{ self.slot.replace_html(view.hemx_key(), super::render(&view)) }}\n"));
        out.push_str(&format!("{inner}    pub fn append_keyed(self, key: impl ::std::string::ToString, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect {{ self.slot.append_html(key.to_string(), super::render(view)) }}\n"));
        out.push_str(&format!("{inner}    pub fn prepend_keyed(self, key: impl ::std::string::ToString, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect {{ self.slot.prepend_html(key.to_string(), super::render(view)) }}\n"));
        out.push_str(&format!("{inner}    pub fn replace_keyed(self, key: impl ::std::string::ToString, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect {{ self.slot.replace_html(key.to_string(), super::render(view)) }}\n"));
        out.push_str(&format!("{inner}    pub fn remove(self, key: impl ::std::string::ToString) -> ::hemx::advanced::Effect {{ self.slot.remove(key.to_string()) }}\n"));
        out.push_str(&format!("{inner}}}\n"));
        out.push_str(&format!(
            "{inner}impl<K: ::std::string::ToString, T> ::hemx::GeneratedTarget for KeyedSlotTarget<K, T> {{\n"
        ));
        out.push_str(&format!("{inner}    fn __hemx_resource_id(self) -> ::hemx::advanced::ResourceId {{ self.slot.id() }}\n"));
        out.push_str(&format!("{inner}}}\n"));
        for res in self
            .slots
            .values()
            .filter(|res| component_matches(res, component))
        {
            if res.keyed {
                out.push_str(&format!(
                    "{inner}pub const {}: KeyedSlotTarget<::std::string::String, ::std::string::String> = KeyedSlotTarget::new(super::advanced::slots::{});\n",
                    res.ident, res.ident
                ));
            } else {
                out.push_str(&format!(
                    "{inner}pub const {}: SlotTarget<::std::string::String> = SlotTarget::new(super::advanced::slots::{});\n",
                    res.ident, res.ident
                ));
            }
        }
        out.push_str(&format!("{pad}}}\n"));
        for res in self
            .slots
            .values()
            .filter(|res| component_matches(res, component))
        {
            push_root_export(
                out,
                &pad,
                "targets",
                &mut root_exports,
                &res.ident,
                "target",
            );
        }
        out.push_str("\n");

        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod handles {{\n"
        ));
        for res in self
            .handles
            .values()
            .filter(|res| component_matches(res, component))
        {
            handle_ids.push(res.id);
            let input = if self.handle_forms.contains_key(&res.ident) {
                "::hemx::Form<::std::string::String>"
            } else {
                "()"
            };
            out.push_str(&format!(
                "{inner}pub const {}: ::hemx::Handle<{input}> = ::hemx::Handle::new({});\n",
                res.ident, res.id
            ));
        }
        out.push_str(&format!(
            "{inner}pub const ALL_IDS: &[u32] = &[{}];\n",
            handle_ids
                .into_iter()
                .map(|id| id.to_string())
                .collect::<Vec<_>>()
                .join(", ")
        ));
        out.push_str(&format!("{pad}}}\n"));
        for res in self
            .handles
            .values()
            .filter(|res| component_matches(res, component))
        {
            push_root_export(
                out,
                &pad,
                "handles",
                &mut root_exports,
                &res.ident,
                "handle",
            );
        }
        out.push_str("\n");

        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod params {{\n"
        ));
        let mut emitted_params = BTreeSet::new();
        for res in self
            .handles
            .values()
            .filter(|res| component_matches(res, component))
        {
            if let Some(params) = self.handle_params.get(&res.ident) {
                for param in params {
                    if emitted_params.insert(param.as_str()) {
                        out.push_str(&format!(
                            "{inner}pub const {param}: ::hemx::ParamName = ::hemx::ParamName::new({});\n",
                            rust_str(param)
                        ));
                    }
                }
            }
        }
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod atoms {{\n"
        ));
        for res in self
            .atoms
            .values()
            .filter(|res| component_matches(res, component))
        {
            out.push_str(&format!(
                "{inner}pub const {}: ::hemx::Atom<::std::string::String> = ::hemx::Atom::new({});\n",
                res.ident, res.id
            ));
        }
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod classes {{\n"
        ));
        let mut emitted_classes = BTreeSet::new();
        for class in self
            .classes
            .values()
            .filter(|class| class_matches(class, component))
        {
            if !emitted_classes.insert(class.ident.as_str()) {
                continue;
            }
            out.push_str(&format!(
                "{inner}pub const {}: ::hemx::CssClass = ::hemx::CssClass::new({});\n",
                class.ident,
                rust_str(&class.token)
            ));
        }
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod events {{\n"
        ));
        let mut emitted_events = BTreeSet::new();
        for event in self
            .events
            .values()
            .filter(|event| event_matches(event, component))
        {
            if !emitted_events.insert(event.ident.as_str()) {
                continue;
            }
            out.push_str(&format!(
                "{inner}pub const {}: ::hemx::EventName = ::hemx::EventName::new({});\n",
                event.ident,
                rust_str(&event.name)
            ));
        }
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!(
            "{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod forms {{\n"
        ));
        for form in self
            .forms
            .values()
            .filter(|form| component_matches(&form.resource, component))
        {
            let res = &form.resource;
            out.push_str(&format!(
                "{inner}pub const {}: ::hemx::Form<::std::string::String> = ::hemx::Form::new({});\n",
                res.ident, res.id
            ));
            out.push_str(&format!(
                "{inner}pub const {}_CONTRACT: ::hemx::FormContract = ::hemx::FormContract {{ fields: &{}_FIELDS }};\n",
                res.ident.to_ascii_uppercase(), res.ident.to_ascii_uppercase()
            ));
            out.push_str(&format!(
                "{inner}pub const {}_FIELDS: &[::hemx::FormField] = &[\n",
                res.ident.to_ascii_uppercase()
            ));
            for control in &form.controls {
                out.push_str(&format!(
                    "{inner}    ::hemx::FormField {{ name: {}, kind: {}, required: {} }},\n",
                    rust_str(&control.name),
                    form_control_kind_expr(&control.kind),
                    control.required
                ));
            }
            out.push_str(&format!("{inner}];\n"));
        }
        out.push_str(&format!("{pad}}}\n"));
        for form in self
            .forms
            .values()
            .filter(|form| component_matches(&form.resource, component))
        {
            push_root_export(
                out,
                &pad,
                "forms",
                &mut root_exports,
                &form.resource.ident,
                "form",
            );
        }
    }

    fn push_lowering_api(&self, out: &mut String, component: Option<&str>, indent: usize) {
        let pad = "    ".repeat(indent);
        let table_name = match component {
            Some(component) => format!("__HEMX_LOWERING_TABLE_{}", component.to_ascii_uppercase()),
            None => "__HEMX_LOWERING_TABLE".to_string(),
        };
        out.push_str(&format!("\n{pad}pub fn lower(html: impl ::std::convert::AsRef<str>) -> ::std::string::String {{\n"));
        out.push_str(&format!("{pad}    "));
        if component.is_some() {
            out.push_str("super::");
        }
        out.push_str(&format!(
            "__hemx_lower_html(html.as_ref(), &{table_name})\n"
        ));
        out.push_str(&format!("{pad}}}\n\n"));
        out.push_str(&format!("{pad}#[doc(hidden)]\n"));
        out.push_str(&format!("{pad}pub fn lower_html(html: impl ::std::convert::AsRef<str>) -> ::std::string::String {{ lower(html) }}\n\n"));
        out.push_str(&format!(
            "{pad}pub fn static_fragment(html: &'static str) -> ::hemx::Html {{\n"
        ));
        out.push_str(&format!(
            "{pad}    ::hemx::__private::html_trusted(lower(html))\n"
        ));
        out.push_str(&format!("{pad}}}\n\n"));
        out.push_str(&format!(
            "{pad}pub fn render(view: &impl ::hemplate::Hemplate) -> ::hemx::Html {{\n"
        ));
        out.push_str(&format!(
            "{pad}    let mut html = ::std::string::String::new();\n"
        ));
        out.push_str(&format!("{pad}    ::hemplate::Hemplate::render_into(view, &mut html).expect(\"hemx hemplate view renders\");\n"));
        out.push_str(&format!(
            "{pad}    ::hemx::__private::html_trusted(lower(html))\n"
        ));
        out.push_str(&format!("{pad}}}\n\n"));
        out.push_str(&format!(
            "{pad}pub fn page(view: &impl ::hemplate::Hemplate) -> ::hemx::Html {{ render(view) }}\n\n"
        ));
        out.push_str(&format!("{pad}#[doc(hidden)]\n"));
        out.push_str(&format!("{pad}pub fn render_html(view: &impl ::hemplate::Hemplate) -> ::hemx::Html {{ render(view) }}\n\n"));
        out.push_str(&format!("{pad}#[doc(hidden)]\n"));
        out.push_str(&format!("{pad}pub fn put<T>(slot: ::hemx::advanced::Slot<T>, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect {{\n"));
        out.push_str(&format!("{pad}    slot.html(render(view))\n"));
        out.push_str(&format!("{pad}}}\n\n"));
        out.push_str(&format!("{pad}#[doc(hidden)]\n"));
        out.push_str(&format!("{pad}pub fn append<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect\n"));
        out.push_str(&format!("{pad}where\n"));
        out.push_str(&format!("{pad}    K: ::std::string::ToString,\n"));
        out.push_str(&format!("{pad}{{\n"));
        out.push_str(&format!("{pad}    slot.append_html(key, render(view))\n"));
        out.push_str(&format!("{pad}}}\n\n"));
        out.push_str(&format!("{pad}#[doc(hidden)]\n"));
        out.push_str(&format!("{pad}pub fn prepend<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect\n"));
        out.push_str(&format!("{pad}where\n"));
        out.push_str(&format!("{pad}    K: ::std::string::ToString,\n"));
        out.push_str(&format!("{pad}{{\n"));
        out.push_str(&format!("{pad}    slot.prepend_html(key, render(view))\n"));
        out.push_str(&format!("{pad}}}\n\n"));
        out.push_str(&format!("{pad}#[doc(hidden)]\n"));
        out.push_str(&format!("{pad}pub fn replace<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect\n"));
        out.push_str(&format!("{pad}where\n"));
        out.push_str(&format!("{pad}    K: ::std::string::ToString,\n"));
        out.push_str(&format!("{pad}{{\n"));
        out.push_str(&format!("{pad}    slot.replace_html(key, render(view))\n"));
        out.push_str(&format!("{pad}}}\n\n"));
        self.push_lowering_table(out, component, indent, &table_name);
    }

    fn push_lowering_table(
        &self,
        out: &mut String,
        component: Option<&str>,
        indent: usize,
        name: &str,
    ) {
        let pad = "    ".repeat(indent);
        out.push_str(&format!("{pad}const {name}: &[(&str, &str, u32)] = &[\n"));
        for res in self
            .slots
            .values()
            .filter(|res| component_matches(res, component))
        {
            out.push_str(&format!(
                "{pad}    (\"data-hemx-slot\", {}, {}),\n",
                rust_str(&res.ident),
                res.id
            ));
        }
        for res in self
            .handles
            .values()
            .filter(|res| component_matches(res, component))
        {
            out.push_str(&format!(
                "{pad}    (\"data-hemx-handle\", {}, {}),\n",
                rust_str(&res.ident),
                res.id
            ));
        }
        for form in self
            .forms
            .values()
            .filter(|form| component_matches(&form.resource, component))
        {
            let res = &form.resource;
            out.push_str(&format!(
                "{pad}    (\"data-hemx-form\", {}, {}),\n",
                rust_str(&res.ident),
                res.id
            ));
        }
        for res in self
            .atoms
            .values()
            .filter(|res| component_matches(res, component))
        {
            out.push_str(&format!(
                "{pad}    (\"data-hemx-atom\", {}, {}),\n",
                rust_str(&res.ident),
                res.id
            ));
        }
        out.push_str(&format!("{pad}];\n"));
    }

    fn push_lowering_helpers(&self, out: &mut String) {
        out.push_str(r#"
fn __hemx_lower_html(html: &str, table: &[(&str, &str, u32)]) -> ::std::string::String {
    let mut out = html.to_owned();
    for (attr, name, id) in table {
        let runtime_attr = match *attr {
            "data-hemx-slot" => "data-sid",
            "data-hemx-handle" => "data-hid",
            "data-hemx-form" => "data-fid",
            "data-hemx-atom" => "data-aid",
            _ => continue,
        };
        out = __hemx_replace_attr(out, attr, name, runtime_attr, *id);
    }
    out = __hemx_lower_static_attr(out, "data-hemx-key", "data-key");
    __hemx_inject_handle_inputs(out)
}

fn __hemx_replace_attr(mut html: ::std::string::String, attr: &str, name: &str, runtime_attr: &str, id: u32) -> ::std::string::String {
    let replacement = if runtime_attr == "value" {
        ::std::format!("{attr}=\"{name}\" {runtime_attr}=\"{id}\"")
    } else {
        ::std::format!("{runtime_attr}=\"{id}\"")
    };
    let double = ::std::format!("{attr}=\"{name}\"");
    html = html.replace(&double, &replacement);
    let single_replacement = replacement.replace('"', "'");
    let single = ::std::format!("{attr}='{name}'");
    html.replace(&single, &single_replacement)
}

fn __hemx_lower_static_attr(mut html: ::std::string::String, attr: &str, runtime_attr: &str) -> ::std::string::String {
    html = html.replace(&::std::format!("{attr}=\""), &::std::format!("{runtime_attr}=\""));
    html.replace(&::std::format!("{attr}='"), &::std::format!("{runtime_attr}='"))
}

fn __hemx_inject_handle_inputs(html: ::std::string::String) -> ::std::string::String {
    let mut out = ::std::string::String::with_capacity(html.len());
    let mut rest = html.as_str();
    while let Some(start) = rest.find("<form") {
        out.push_str(&rest[..start]);
        rest = &rest[start..];
        let Some(open_end) = rest.find('>') else {
            out.push_str(rest);
            return out;
        };
        let opening = &rest[..=open_end];
        out.push_str(opening);
        rest = &rest[open_end + 1..];

        let Some(handle_id) = __hemx_attr(opening, "data-hid") else {
            continue;
        };
        let form_body_end = rest.find("</form>").unwrap_or(rest.len());
        let form_body = &rest[..form_body_end];
        if !__hemx_has_handle_input(form_body) {
            out.push_str(&::std::format!("<input type=\"hidden\" name=\"__h\" value=\"{}\">", handle_id));
        }
    }
    out.push_str(rest);
    out
}

fn __hemx_has_handle_input(html: &str) -> bool {
    html.contains("name=\"__h\"") || html.contains("name='__h'")
}

fn __hemx_attr(tag: &str, attr: &str) -> Option<::std::string::String> {
    let attr_at = tag.find(attr)?;
    let after_attr = &tag[attr_at + attr.len()..];
    let after_equals = after_attr.trim_start().strip_prefix('=')?.trim_start();
    let quote = after_equals.chars().next()?;
    if quote != '\"' && quote != '\'' {
        return None;
    }
    let value = &after_equals[quote.len_utf8()..];
    let end = value.find(quote)?;
    Some(value[..end].to_owned())
}
"#);
    }

    fn component_names(&self) -> Vec<String> {
        let mut components = Vec::new();
        for component in self
            .slots
            .values()
            .map(|res| &res.component)
            .chain(self.handles.values().map(|res| &res.component))
            .chain(self.atoms.values().map(|res| &res.component))
            .chain(self.forms.values().map(|form| &form.resource.component))
            .chain(self.classes.values().map(|class| &class.component))
            .chain(self.events.values().map(|event| &event.component))
        {
            if !components.contains(component) {
                components.push(component.clone());
            }
        }
        components.sort();
        components
    }

    fn syms(&self) -> String {
        let mut out = String::from("hemx-syms-v1\n");
        for res in self.slots.values() {
            out.push_str(&format!(
                "slot\t{}\t{}\t{}\n",
                res.symbol, res.ident, res.id
            ));
        }
        for res in self.handles.values() {
            out.push_str(&format!(
                "handle\t{}\t{}\t{}\n",
                res.symbol, res.ident, res.id
            ));
        }
        for form in self.forms.values() {
            let res = &form.resource;
            out.push_str(&format!(
                "form\t{}\t{}\t{}\n",
                res.symbol, res.ident, res.id
            ));
        }
        for (handle_ident, form_ident) in &self.handle_forms {
            out.push_str(&format!("handle_form\t{handle_ident}\t{form_ident}\n"));
        }
        for form in self.forms.values() {
            for control in &form.controls {
                out.push_str(&format!(
                    "form_field\t{}\t{}\t{}\t{}\n",
                    form.resource.ident,
                    control.name,
                    control.required,
                    form_control_is_multiple(&control.kind)
                ));
            }
        }
        for (handle_ident, params) in &self.handle_params {
            for param in params {
                out.push_str(&format!("handle_param\t{handle_ident}\t{param}\n"));
            }
        }
        for res in self.atoms.values() {
            out.push_str(&format!(
                "atom\t{}\t{}\t{}\n",
                res.symbol, res.ident, res.id
            ));
        }
        for class in self.classes.values() {
            out.push_str(&format!(
                "class\t{}\t{}\t{}\n",
                class.symbol, class.ident, class.token
            ));
        }
        for event in self.events.values() {
            out.push_str(&format!(
                "event\t{}\t{}\t{}\n",
                event.symbol, event.ident, event.name
            ));
        }
        out
    }

    fn fingerprint_parts(&self) -> Vec<u32> {
        let mut parts = vec![
            SURFACE_SCHEMA_VERSION,
            EFFECT_BATCH_ABI_VERSION,
            RUNTIME_ABI_VERSION,
        ];

        for res in self.slots.values() {
            parts.push(0);
            parts.push(res.id);
        }
        for res in self.handles.values() {
            parts.push(1);
            parts.push(res.id);
        }
        for res in self.atoms.values() {
            parts.push(3);
            parts.push(res.id);
        }
        for form in self.forms.values() {
            parts.push(2);
            parts.push(form.resource.id);
            parts.push(form.controls.len() as u32);
            for control in &form.controls {
                parts.push(stable_id("form-field", &control.name));
                parts.push(control.required as u32);
            }
        }

        parts
    }
}

fn insert_resource(
    map: &mut BTreeMap<String, Resource>,
    kind: &str,
    symbol: String,
    name: String,
    component: String,
    keyed: bool,
) -> io::Result<()> {
    let resource = make_resource(kind, symbol, name, component, keyed)?;
    match map.get_mut(&resource.ident) {
        Some(existing) if existing.symbol != resource.symbol => Err(io::Error::new(
            io::ErrorKind::InvalidData,
            format!(
                "duplicate generated identifier `{}` for `{}` and `{}`",
                resource.ident, existing.symbol, resource.symbol
            ),
        )),
        Some(existing) => {
            existing.keyed |= keyed;
            Ok(())
        }
        None => {
            map.insert(resource.ident.clone(), resource);
            Ok(())
        }
    }
}

fn make_resource(
    kind: &str,
    symbol: String,
    name: String,
    component: String,
    keyed: bool,
) -> io::Result<Resource> {
    let ident = rust_ident(&name).ok_or_else(|| {
        io::Error::new(
            io::ErrorKind::InvalidData,
            format!("invalid hemx {kind} name `{name}`; expected a Rust identifier"),
        )
    })?;
    let id = stable_id(kind, &symbol);
    Ok(Resource {
        symbol,
        ident,
        component,
        keyed,
        id,
    })
}

fn collect_heml(root: &Path) -> io::Result<Vec<PathBuf>> {
    let mut paths = Vec::new();
    if !root.exists() {
        return Ok(paths);
    }
    collect_heml_into(root, &mut paths)?;
    paths.sort();
    Ok(paths)
}

fn collect_heml_into(dir: &Path, paths: &mut Vec<PathBuf>) -> io::Result<()> {
    for entry in std::fs::read_dir(dir)? {
        let entry = entry?;
        let path = entry.path();
        if path.is_dir() {
            collect_heml_into(&path, paths)?;
        } else if path.extension().and_then(|ext| ext.to_str()) == Some("heml") {
            paths.push(path);
        }
    }
    Ok(())
}

fn collect_stylesheets(root: &Path) -> io::Result<Vec<PathBuf>> {
    let mut paths = Vec::new();
    if !root.exists() {
        return Ok(paths);
    }
    collect_stylesheets_into(root, &mut paths)?;
    paths.sort();
    Ok(paths)
}

fn collect_stylesheets_into(dir: &Path, paths: &mut Vec<PathBuf>) -> io::Result<()> {
    for entry in std::fs::read_dir(dir)? {
        let entry = entry?;
        let path = entry.path();
        if path.is_dir() {
            collect_stylesheets_into(&path, paths)?;
        } else if matches!(
            path.extension().and_then(|ext| ext.to_str()),
            Some("css" | "scss")
        ) {
            paths.push(path);
        }
    }
    Ok(())
}

fn static_attr(attrs: &[SurfaceAttribute], name: &str) -> Option<String> {
    attrs
        .iter()
        .find(|attr| attr.origin == AttributeOrigin::Static && attr.name == name)
        .and_then(|attr| attr.value.clone())
}

fn push_root_export(
    out: &mut String,
    pad: &str,
    module: &str,
    used: &mut BTreeSet<String>,
    ident: &str,
    suffix: &str,
) {
    if used.insert(ident.to_owned()) {
        out.push_str(&format!("{pad}pub use self::{module}::{ident};\n"));
        return;
    }
    let alias = format!("{ident}_{suffix}");
    if used.insert(alias.clone()) {
        out.push_str(&format!(
            "{pad}pub use self::{module}::{ident} as {alias};\n"
        ));
    }
}

fn component_matches(res: &Resource, component: Option<&str>) -> bool {
    match component {
        Some(component) => res.component == component,
        None => true,
    }
}

fn class_matches(class: &ClassToken, component: Option<&str>) -> bool {
    match component {
        Some(component) => class.component == component,
        None => true,
    }
}

fn event_matches(event: &EventToken, component: Option<&str>) -> bool {
    match component {
        Some(component) => event.component == component,
        None => true,
    }
}

fn class_tokens(value: &str) -> impl Iterator<Item = &str> {
    value
        .split_ascii_whitespace()
        .filter(|token| !token.is_empty())
}

fn event_tokens(value: &str) -> impl Iterator<Item = &str> {
    value
        .split_ascii_whitespace()
        .filter(|token| !token.is_empty())
}

fn stylesheet_class_tokens(source: &str) -> Vec<&str> {
    let bytes = source.as_bytes();
    let mut tokens = Vec::new();
    let mut i = 0;
    while i < bytes.len() {
        if bytes[i] != b'.' {
            i += 1;
            continue;
        }
        let prev = i.checked_sub(1).map(|idx| bytes[idx]);
        if prev.is_some_and(|ch| ch == b'-' || ch == b'_' || ch.is_ascii_alphanumeric())
            && !preceded_by_class_in_compound(bytes, i)
        {
            i += 1;
            continue;
        }
        let start = i + 1;
        if start >= bytes.len() || !is_class_start(bytes[start]) {
            i += 1;
            continue;
        }
        let mut end = start + 1;
        while end < bytes.len() && is_class_continue(bytes[end]) {
            end += 1;
        }
        if let Ok(token) = std::str::from_utf8(&bytes[start..end]) {
            tokens.push(token);
        }
        i = end;
    }
    tokens.sort_unstable();
    tokens.dedup();
    tokens
}

fn preceded_by_class_in_compound(bytes: &[u8], dot: usize) -> bool {
    let mut i = dot;
    while let Some(prev) = i.checked_sub(1) {
        let byte = bytes[prev];
        if byte == b'.' {
            return true;
        }
        if matches!(
            byte,
            b' ' | b'\n' | b'\r' | b'\t' | b',' | b'{' | b'}' | b'>' | b'+' | b'~' | b'(' | b')'
        ) {
            return false;
        }
        i = prev;
    }
    false
}

fn is_class_start(byte: u8) -> bool {
    byte == b'_' || byte == b'-' || byte.is_ascii_alphabetic()
}

fn is_class_continue(byte: u8) -> bool {
    is_class_start(byte) || byte.is_ascii_digit()
}

fn class_ident(token: &str) -> Option<String> {
    let mut ident = String::with_capacity(token.len());
    for ch in token.chars() {
        match ch {
            '-' => ident.push('_'),
            '_' => ident.push('_'),
            ch if ch.is_ascii_alphanumeric() => ident.push(ch),
            _ => return None,
        }
    }
    rust_ident(&ident)
}

fn is_handle_param_attr(attr: &SurfaceAttribute) -> bool {
    matches!(
        attr.origin,
        AttributeOrigin::Static | AttributeOrigin::Dynamic
    ) && attr.name.starts_with("data-")
        && !attr.name.starts_with("data-hemx-")
}

fn data_param_ident(name: &str) -> Option<String> {
    let data_name = name.strip_prefix("data-")?;
    rust_ident(&data_name.replace('-', "_"))
}

fn event_ident(name: &str) -> Option<String> {
    rust_ident(&name.replace(['-', ':'], "_"))
}

fn can_host_keyed_collection(tag: &str) -> bool {
    matches!(
        tag,
        "ul" | "ol" | "tbody" | "thead" | "tfoot" | "table" | "select" | "datalist"
    )
}

fn has_descendant_keyed_for_scope(surface: &SurfaceDocument, scope: ScopeId) -> bool {
    surface.scopes.iter().enumerate().any(|(index, current)| {
        matches!(
            current.kind,
            ScopeKind::For {
                key_expr: Some(_),
                ..
            }
        ) && is_descendant_scope(surface, ScopeId(index as u32), scope)
    })
}

fn is_descendant_scope(surface: &SurfaceDocument, mut scope: ScopeId, ancestor: ScopeId) -> bool {
    loop {
        let Some(current) = surface.scopes.get(scope.0 as usize) else {
            return false;
        };
        let Some(parent) = current.parent else {
            return false;
        };
        if parent == ancestor {
            return true;
        }
        scope = parent;
    }
}

fn is_inside_keyed_for(surface: &SurfaceDocument, mut scope: ScopeId) -> bool {
    loop {
        let Some(current) = surface.scopes.get(scope.0 as usize) else {
            return false;
        };
        if matches!(
            current.kind,
            ScopeKind::For {
                key_expr: Some(_),
                ..
            }
        ) {
            return true;
        }
        let Some(parent) = current.parent else {
            return false;
        };
        scope = parent;
    }
}

fn reject_selector_target_attrs(path: &Path, attrs: &[SurfaceAttribute]) -> io::Result<()> {
    for attr in attrs {
        let name = attr.name.as_str();
        if matches!(name, "data-hemx-target" | "data-hemx-select") {
            return Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "{}: `{name}` is selector-style targeting; hemx uses generated resources instead. Add data-hemx-slot to the local element and return an effect for that generated slot.",
                    path.display()
                ),
            ));
        }
    }
    Ok(())
}

fn reject_unknown_hemx_attrs(path: &Path, attrs: &[SurfaceAttribute]) -> io::Result<()> {
    for attr in attrs {
        let name = attr.name.as_str();
        if name.starts_with("data-hemx-") && !known_hemx_attr(name) {
            return Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "{}: unknown hemx attribute `{name}`; check the spelling or use a non-hemx data-* attribute for app-specific metadata",
                    path.display()
                ),
            ));
        }
    }
    Ok(())
}

fn known_hemx_attr(name: &str) -> bool {
    matches!(
        name,
        "data-hemx-root"
            | "data-hemx-sse"
            | "data-hemx-st"
            | "data-hemx-handle"
            | "data-hemx-slot"
            | "data-hemx-form"
            | "data-hemx-atom"
            | "data-hemx-key"
            | "data-hemx-on"
            | "data-hemx-pending-class"
            | "data-hemx-indicator"
            | "data-hemx-confirm"
            | "data-hemx-debounce"
            | "data-hemx-throttle"
            | "data-hemx-every"
            | "data-hemx-disable-while-pending"
            | "data-hemx-policy"
            | "data-hemx-nav"
            | "data-hemx-boost"
            | "data-hemx-error-for"
            | "data-hemx-island"
    )
}

fn reject_invalid_hemx_attr_values(path: &Path, attrs: &[SurfaceAttribute]) -> io::Result<()> {
    for attr in attrs
        .iter()
        .filter(|attr| attr.origin == AttributeOrigin::Static)
    {
        let value = attr.value.as_deref().unwrap_or("");
        match attr.name.as_str() {
            "data-hemx-policy" if !valid_policy(value) => {
                return Err(invalid_hemx_value(
                    path,
                    &attr.name,
                    value,
                    "expected one of `latest`, `queue`, `drop`, or `parallel`",
                ));
            }
            "data-hemx-on" if !valid_event_list(value) => {
                return Err(invalid_hemx_value(
                    path,
                    &attr.name,
                    value,
                    "expected runtime-supported events: `click`, `submit`, `input`, `change`, `dragstart`, `dragover`, or `drop`",
                ));
            }
            "data-hemx-confirm" if value.trim().is_empty() => {
                return Err(invalid_hemx_value(
                    path,
                    &attr.name,
                    value,
                    "expected a non-empty confirmation message",
                ));
            }
            "data-hemx-sse" if value.trim().is_empty() => {
                return Err(invalid_hemx_value(
                    path,
                    &attr.name,
                    value,
                    "expected a non-empty same-origin SSE URL",
                ));
            }
            "data-hemx-debounce" | "data-hemx-throttle" | "data-hemx-every"
                if !valid_duration(value) =>
            {
                return Err(invalid_hemx_value(
                    path,
                    &attr.name,
                    value,
                    "expected milliseconds like `250`/`250ms` or seconds like `1s`",
                ));
            }
            _ => {}
        }
    }
    Ok(())
}

fn reject_invalid_hemx_attr_placement(
    path: &Path,
    tag: &str,
    attrs: &[SurfaceAttribute],
) -> io::Result<()> {
    if has_attr(attrs, "data-hemx-nav")
        && (tag != "a"
            || !has_attr(attrs, "href")
            || static_attr(attrs, "href").is_some_and(|href| href.trim().is_empty()))
    {
        return Err(invalid_hemx_placement(
            path,
            "data-hemx-nav",
            "expected a real `<a href=...>` link so navigation works without JavaScript",
        ));
    }
    if has_attr(attrs, "data-hemx-boost") && matches!(tag, "a" | "form") {
        return Err(invalid_hemx_placement(
            path,
            "data-hemx-boost",
            "expected a container around descendant links/forms; use `data-hemx-nav` on anchors or `data-hemx-handle` on forms",
        ));
    }
    if has_attr(attrs, "data-hemx-sse") && !has_attr(attrs, "data-hemx-root") {
        return Err(invalid_hemx_placement(
            path,
            "data-hemx-sse",
            "expected placement on the same element as `data-hemx-root`",
        ));
    }
    Ok(())
}

fn has_attr(attrs: &[SurfaceAttribute], name: &str) -> bool {
    attrs.iter().any(|attr| attr.name == name)
}

fn invalid_hemx_placement(path: &Path, attr: &str, expectation: &str) -> io::Error {
    io::Error::new(
        io::ErrorKind::InvalidData,
        format!(
            "{}: invalid {attr} placement; {expectation}",
            path.display()
        ),
    )
}

fn valid_policy(value: &str) -> bool {
    matches!(value.trim(), "latest" | "queue" | "drop" | "parallel")
}

fn valid_event_list(value: &str) -> bool {
    let mut events = event_tokens(value).peekable();
    events.peek().is_some() && events.all(valid_runtime_event)
}

fn valid_runtime_event(value: &str) -> bool {
    matches!(
        value,
        "click" | "submit" | "input" | "change" | "dragstart" | "dragover" | "drop"
    )
}

fn valid_duration(value: &str) -> bool {
    let value = value.trim();
    let digits = value
        .strip_suffix("ms")
        .or_else(|| value.strip_suffix('s'))
        .unwrap_or(value);
    !digits.is_empty() && digits.as_bytes().iter().all(u8::is_ascii_digit)
}

fn invalid_hemx_value(path: &Path, attr: &str, value: &str, expectation: &str) -> io::Error {
    io::Error::new(
        io::ErrorKind::InvalidData,
        format!(
            "{}: invalid {attr} value `{value}`; {expectation}",
            path.display()
        ),
    )
}

fn reject_unkeyed_loop(
    surface: &SurfaceDocument,
    mut scope: ScopeId,
    path: &Path,
    kind: &str,
    name: &str,
) -> io::Result<()> {
    loop {
        let Some(current) = surface.scopes.get(scope.0 as usize) else {
            return Ok(());
        };
        if matches!(current.kind, ScopeKind::For { key_expr: None, .. }) {
            return Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "{}: data-hemx-{kind}=\"{name}\" is inside an h-for without h-key; add a stable h-key=\"item.id\" to the loop that owns this generated target",
                    path.display()
                ),
            ));
        }
        let Some(parent) = current.parent else {
            return Ok(());
        };
        scope = parent;
    }
}

fn canonical_symbol(root: &Path, path: &Path, name: &str) -> String {
    let rel = path.strip_prefix(root).unwrap_or(path);
    format!("{}::{name}", rel.to_string_lossy().replace('\\', "/"))
}

fn component_ident(root: &Path, path: &Path) -> io::Result<String> {
    let rel = path.strip_prefix(root).unwrap_or(path);
    let stem = rel
        .file_stem()
        .and_then(|stem| stem.to_str())
        .ok_or_else(|| {
            io::Error::new(
                io::ErrorKind::InvalidData,
                format!("invalid template path `{}`", path.display()),
            )
        })?;
    rust_ident(stem).ok_or_else(|| {
        io::Error::new(
            io::ErrorKind::InvalidData,
            format!("invalid template name `{stem}`; expected a Rust module identifier"),
        )
    })
}

fn rust_ident(name: &str) -> Option<String> {
    let mut chars = name.chars();
    let first = chars.next()?;
    if !(first == '_' || first.is_ascii_alphabetic()) {
        return None;
    }
    if chars
        .clone()
        .any(|ch| !(ch == '_' || ch.is_ascii_alphanumeric()))
    {
        return None;
    }
    Some(name.to_string())
}

fn stable_id(kind: &str, symbol: &str) -> u32 {
    let mut hash = 0x811c9dc5u32;
    for byte in kind.bytes().chain([b':']).chain(symbol.bytes()) {
        hash ^= byte as u32;
        hash = hash.wrapping_mul(0x01000193);
    }
    hash
}

fn form_control_is_multiple(kind: &ControlKind) -> bool {
    matches!(kind, ControlKind::Select { multiple: true })
}

fn form_control_kind_expr(kind: &ControlKind) -> String {
    match kind {
        ControlKind::Text => "::hemx::FormControlKind::Text".to_string(),
        ControlKind::Number { min, max, step } => format!(
            "::hemx::FormControlKind::Number {{ min: {}, max: {}, step: {} }}",
            rust_str_opt(min.as_deref()),
            rust_str_opt(max.as_deref()),
            rust_str_opt(step.as_deref())
        ),
        ControlKind::Checkbox => "::hemx::FormControlKind::Checkbox".to_string(),
        ControlKind::Radio => "::hemx::FormControlKind::Radio".to_string(),
        ControlKind::Select { multiple } => {
            format!("::hemx::FormControlKind::Select {{ multiple: {multiple} }}")
        }
        ControlKind::TextArea => "::hemx::FormControlKind::TextArea".to_string(),
        ControlKind::File => "::hemx::FormControlKind::File".to_string(),
        ControlKind::Hidden => "::hemx::FormControlKind::Hidden".to_string(),
        ControlKind::Submit => "::hemx::FormControlKind::Submit".to_string(),
        ControlKind::Other { tag, input_type } => format!(
            "::hemx::FormControlKind::Other {{ tag: {}, input_type: {} }}",
            rust_str(tag),
            rust_str_opt(input_type.as_deref())
        ),
    }
}

fn rust_str(value: &str) -> String {
    format!("{value:?}")
}

fn rust_str_opt(value: Option<&str>) -> String {
    match value {
        Some(value) => format!("Some({})", rust_str(value)),
        None => "None".to_string(),
    }
}

fn parse_error(path: &Path, err: impl std::fmt::Display) -> io::Error {
    io::Error::new(
        io::ErrorKind::InvalidData,
        format!("failed to parse {}: {err}", path.display()),
    )
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn emits_generated_resources_from_heml() {
        // req: codegen/003
        let base = test_dir("hemx-build-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("todo.heml"),
            r#"<form data-hemx-handle="create" data-hemx-form="new_todo"><input name="title"></form><button data-hemx-handle="delete" data-todo-id="7" data-hemx-on="click change">Delete</button><ul data-hemx-slot="todos"></ul><section data-hemx-atom="filter"></section>"#,
        )
        .unwrap();

        app()
            .template_dir(&templates)
            .out_dir(&out)
            .global_exports(true)
            .run()
            .unwrap();

        let generated = std::fs::read_to_string(out.join("hemx.generated.rs")).unwrap();
        assert!(generated.contains("pub mod components"));
        assert!(generated.contains(
            "pub const todo: ::hemx::ComponentRef = ::hemx::ComponentRef::new(\"todo\")"
        ));
        assert!(generated.contains("pub mod advanced"));
        assert!(generated.contains("pub mod slots"));
        assert!(generated.contains("pub const todos"));
        assert!(generated.contains("pub mod targets"));
        assert!(generated.contains("pub struct SlotTarget<T>"));
        assert!(generated.contains("impl<T> ::hemx::GeneratedTarget for SlotTarget<T>"));
        assert!(generated.contains(
            "impl<K: ::std::string::ToString, T> ::hemx::GeneratedTarget for KeyedSlotTarget<K, T>"
        ));
        assert!(generated.contains(
            "pub fn append(self, view: impl ::hemplate::Hemplate + ::hemx::KeyedPartial) -> ::hemx::advanced::Effect"
        ));
        assert!(generated.contains(
            "pub fn append_keyed(self, key: impl ::std::string::ToString, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"
        ));
        assert!(generated.contains("pub const todos: SlotTarget<::std::string::String> = SlotTarget::new(super::advanced::slots::todos);"));
        assert!(generated.contains("pub use self::targets::todos;"));
        assert!(generated.contains(
            "pub fn put(self, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"
        ));
        assert!(generated.contains(
            "pub fn replace(self, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"
        ));
        assert!(generated.contains(
            "pub fn set(self, value: impl ::std::string::ToString) -> ::hemx::advanced::Effect"
        ));
        assert!(generated.contains("pub mod handles"));
        assert!(generated
            .contains("pub const create: ::hemx::Handle<::hemx::Form<::std::string::String>>"));
        assert!(generated.contains("pub mod params"));
        assert!(generated.contains(
            "pub const todo_id: ::hemx::ParamName = ::hemx::ParamName::new(\"todo_id\")"
        ));
        assert!(generated.contains("pub mod forms"));
        assert!(generated.contains("pub mod atoms"));
        assert!(generated.contains("pub const filter"));
        assert!(generated.contains("pub mod events"));
        assert!(generated
            .contains("pub const click: ::hemx::EventName = ::hemx::EventName::new(\"click\")"));
        assert!(generated
            .contains("pub const change: ::hemx::EventName = ::hemx::EventName::new(\"change\")"));
        assert!(generated.contains("pub const new_todo"));
        assert!(generated.contains("pub mod todo"));
        assert!(generated.contains("pub const ALL_IDS"));
        assert!(generated.contains(
            "pub fn lower(html: impl ::std::convert::AsRef<str>) -> ::std::string::String"
        ));
        assert!(generated.contains("#[doc(hidden)]\npub fn lower_html"));
        assert!(generated.contains("pub fn static_fragment(html: &'static str) -> ::hemx::Html"));
        assert!(
            generated.contains("pub fn render(view: &impl ::hemplate::Hemplate) -> ::hemx::Html")
        );
        assert!(generated.contains("pub fn page(view: &impl ::hemplate::Hemplate) -> ::hemx::Html"));
        assert!(generated.contains(
            "#[doc(hidden)]\npub fn render_html(view: &impl ::hemplate::Hemplate) -> ::hemx::Html"
        ));
        assert!(generated.contains("pub fn put<T>(slot: ::hemx::advanced::Slot<T>, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));
        assert!(generated.contains("pub fn append<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));
        assert!(generated.contains("pub fn prepend<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));
        assert!(generated.contains("pub fn replace<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));
        assert!(generated.contains("data-hemx-slot"));
        assert!(generated.contains("data-hemx-form"));
        assert!(generated.contains("data-sid"));
        assert!(generated.contains("data-fid"));
        assert!(generated.contains("__hemx_inject_handle_inputs"));

        let syms = std::fs::read_to_string(out.join("hemx.syms")).unwrap();
        assert!(syms.contains("atom\t"));
        assert!(syms.contains("\tfilter\t"));
        assert!(syms.contains("handle_form\tcreate\tnew_todo\n"));
        assert!(syms.contains("handle_param\tdelete\ttodo_id\n"));
        assert!(syms.contains("event\t"));
        assert!(syms.contains("\tclick\tclick\n"));
        assert!(syms.contains("\tchange\tchange\n"));

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn duplicate_collection_slot_upgrades_to_keyed_target() {
        // req: codegen/003 req: list/002
        let base = test_dir("hemx-build-keyed-collection-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("todos.heml"),
            r#"<ul data-hemx-slot="row"><template h-for="todo in &self.todos" h-key="todo.id"><li +data-key="todo.id">{+ todo +}</li></template></ul>"#,
        )
        .unwrap();

        app().template_dir(&templates).out_dir(&out).run().unwrap();

        let generated = std::fs::read_to_string(out.join("hemx.generated.rs")).unwrap();
        assert!(generated.contains("pub const row: ::hemx::advanced::KeyedSlot"));
        assert!(generated.contains("pub const row: KeyedSlotTarget"));
        assert!(generated.contains("pub use self::targets::row;"));
        assert!(!generated.contains("pub const row: SlotTarget"));

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn app_can_consume_precomputed_surface_facts() {
        // req: surface/008 req: build/001
        let base = test_dir("hemx-build-precomputed-surface-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        let path = templates.join("todo.heml");
        let source = Arc::new(
            r#"<button data-hemx-handle="create" data-hemx-on="click">Create</button><div data-hemx-slot="todos"></div>"#
                .to_string(),
        );
        let ast = build_ast(source).unwrap().unwrap();
        let surface = extract_surface(&ast);

        app()
            .template_dir(&templates)
            .out_dir(&out)
            .surface(&path, surface)
            .run()
            .unwrap();

        let generated = std::fs::read_to_string(out.join("hemx.generated.rs")).unwrap();
        assert!(generated.contains("pub mod todo"));
        assert!(generated.contains("pub const create: ::hemx::Handle<()> = ::hemx::Handle::new("));
        assert!(generated.contains("pub const todos: ::hemx::advanced::Slot<::std::string::String> = ::hemx::advanced::Slot::new("));
        assert!(generated.contains("pub const todos: SlotTarget<::std::string::String> = SlotTarget::new(super::advanced::slots::todos);"));
        assert!(generated.contains("pub use self::targets::todos;"));
        assert!(generated
            .contains("pub const click: ::hemx::EventName = ::hemx::EventName::new(\"click\")"));

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn global_resource_exports_are_explicit_opt_in() {
        // req: component/003
        let base = test_dir("hemx-build-no-global-exports-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("todo.heml"),
            r#"<button data-hemx-handle="create">Create</button><div data-hemx-slot="todos"></div>"#,
        )
        .unwrap();

        app().template_dir(&templates).out_dir(&out).run().unwrap();

        let generated = std::fs::read_to_string(out.join("hemx.generated.rs")).unwrap();
        assert!(!generated.contains("\n#[allow(non_upper_case_globals)]\npub mod components"));
        assert!(!generated.contains("\n#[allow(non_upper_case_globals)]\npub mod slots"));
        assert!(generated.contains(
            "\npub fn lower(html: impl ::std::convert::AsRef<str>) -> ::std::string::String"
        ));
        assert!(generated.contains("\n#[doc(hidden)]\npub fn lower_html"));
        assert!(generated.contains("\npub fn static_fragment(html: &'static str) -> ::hemx::Html"));
        assert!(
            generated.contains("\npub fn render(view: &impl ::hemplate::Hemplate) -> ::hemx::Html")
        );
        assert!(
            generated.contains("\npub fn page(view: &impl ::hemplate::Hemplate) -> ::hemx::Html")
        );
        assert!(generated.contains("\n#[doc(hidden)]\npub fn render_html(view: &impl ::hemplate::Hemplate) -> ::hemx::Html"));
        assert!(generated.contains("\npub fn put<T>(slot: ::hemx::advanced::Slot<T>, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));
        assert!(generated.contains("\npub fn append<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));
        assert!(generated.contains("pub mod todo"));
        assert!(generated.contains(
            "    pub const COMPONENT: ::hemx::ComponentRef = ::hemx::ComponentRef::new(\"todo\")"
        ));
        assert!(generated.contains("    pub mod advanced"));
        assert!(generated.contains("    pub mod slots"));
        assert!(generated.contains("    pub mod targets"));
        assert!(generated.contains("    pub const todos: SlotTarget<::std::string::String> = SlotTarget::new(super::advanced::slots::todos);"));
        assert!(generated.contains("    pub use self::targets::todos;"));
        assert!(generated.contains("    #[doc(hidden)]\n    pub fn lower_html"));
        assert!(
            generated.contains("    pub fn page(view: &impl ::hemplate::Hemplate) -> ::hemx::Html")
        );
        assert!(generated.contains("    #[doc(hidden)]\n    pub fn render_html(view: &impl ::hemplate::Hemplate) -> ::hemx::Html"));
        assert!(
            generated.contains("    pub fn static_fragment(html: &'static str) -> ::hemx::Html")
        );
        assert!(generated.contains("    pub fn put<T>(slot: ::hemx::advanced::Slot<T>, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));
        assert!(generated.contains("    pub fn append<K, T>(slot: ::hemx::advanced::KeyedSlot<K, T>, key: K, view: &impl ::hemplate::Hemplate) -> ::hemx::advanced::Effect"));

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn emits_form_contract_metadata_from_surface_controls() {
        // req: codegen/004 req: form/001
        let base = test_dir("hemx-build-form-contract-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("profile.heml"),
            r#"<form data-hemx-handle="save" data-hemx-form="profile">
                <input type="hidden" name="__h" value="123">
                <input name="title" required>
                <input name="count" type="number" min="1" max="10" step="1">
                <select name="labels" multiple></select>
                <input name="avatar" type="file">
            </form>"#,
        )
        .unwrap();

        app().template_dir(&templates).out_dir(&out).run().unwrap();

        let generated = std::fs::read_to_string(out.join("hemx.generated.rs")).unwrap();
        assert!(generated.contains("pub const PROFILE_CONTRACT: ::hemx::FormContract"));
        assert!(generated.contains("pub const PROFILE_FIELDS: &[::hemx::FormField]"));
        assert!(generated.contains(
            "::hemx::FormField { name: \"title\", kind: ::hemx::FormControlKind::Text, required: true }"
        ));
        assert!(generated.contains(
            "::hemx::FormField { name: \"count\", kind: ::hemx::FormControlKind::Number { min: Some(\"1\"), max: Some(\"10\"), step: Some(\"1\") }, required: false }"
        ));
        assert!(generated.contains(
            "::hemx::FormField { name: \"labels\", kind: ::hemx::FormControlKind::Select { multiple: true }, required: false }"
        ));
        assert!(generated.contains(
            "::hemx::FormField { name: \"avatar\", kind: ::hemx::FormControlKind::File, required: false }"
        ));

        let syms = std::fs::read_to_string(out.join("hemx.syms")).unwrap();
        assert!(syms.contains("handle_form\tsave\tprofile\n"));
        assert!(!syms.contains("form_field\tprofile\t__h\t"));
        assert!(syms.contains("form_field\tprofile\ttitle\ttrue\tfalse\n"));
        assert!(syms.contains("form_field\tprofile\tlabels\tfalse\ttrue\n"));

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn emits_checked_css_class_tokens_from_templates_and_stylesheets() {
        // req: style/001, req: codegen/001
        let base = test_dir("hemx-build-classes-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("card.heml"),
            r#"<article class="card is-active" data-hemx-slot="card_body"></article>"#,
        )
        .unwrap();
        std::fs::write(
            templates.join("card.css"),
            r#".card { padding: 1rem; }
.is-active:hover, .drag-handle { cursor: grab; }
.work-card.is-selected { outline: 1px solid currentColor; }
"#,
        )
        .unwrap();
        std::fs::write(
            templates.join("panel.scss"),
            r#".panel-shell { &.is-open { display: block; } }"#,
        )
        .unwrap();

        app()
            .template_dir(&templates)
            .out_dir(&out)
            .global_exports(true)
            .run()
            .unwrap();

        let generated = std::fs::read_to_string(out.join("hemx.generated.rs")).unwrap();
        assert!(generated.contains("pub mod classes"));
        assert!(generated
            .contains("pub const card: ::hemx::CssClass = ::hemx::CssClass::new(\"card\")"));
        assert!(generated.contains(
            "pub const is_active: ::hemx::CssClass = ::hemx::CssClass::new(\"is-active\")"
        ));
        assert!(generated.contains(
            "pub const drag_handle: ::hemx::CssClass = ::hemx::CssClass::new(\"drag-handle\")"
        ));
        assert!(generated.contains(
            "pub const work_card: ::hemx::CssClass = ::hemx::CssClass::new(\"work-card\")"
        ));
        assert!(generated.contains(
            "pub const is_selected: ::hemx::CssClass = ::hemx::CssClass::new(\"is-selected\")"
        ));
        assert!(generated.contains("pub mod card"));
        assert!(generated.contains("pub mod panel"));

        let syms = std::fs::read_to_string(out.join("hemx.syms")).unwrap();
        assert!(syms.contains("class\t"));
        assert!(syms.contains("\tdrag_handle\tdrag-handle"));

        let source = format!(
            r###"
#![allow(dead_code)]
mod hemx {{
    #[derive(Clone, Copy)] pub struct BuildFingerprint;
    impl BuildFingerprint {{ pub const fn from_parts(_: &[u32]) -> Self {{ Self }} }}
    pub struct Effect;
    #[derive(Clone, Copy)] pub struct ResourceId;
    pub trait IntoEffect {{}}
    impl IntoEffect for Effect {{}}
    pub trait GeneratedTarget {{ fn __hemx_resource_id(self) -> ResourceId; }}
    pub trait KeyedPartial {{ fn hemx_key(&self) -> String; }}
    #[derive(Clone, Copy)] pub struct Slot<T>(::std::marker::PhantomData<T>);
    impl<T> Slot<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} pub const fn id(self) -> ResourceId {{ ResourceId }} pub fn html(self, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn text(self, _: impl ::std::string::ToString) -> Effect {{ Effect }} }}
    #[derive(Clone, Copy)] pub struct KeyedSlot<K, T>(::std::marker::PhantomData<(K, T)>);
    impl<K, T> KeyedSlot<K, T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} pub const fn id(self) -> ResourceId {{ ResourceId }} pub fn append_html(self, _: K, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn prepend_html(self, _: K, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn replace_html(self, _: K, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn remove(self, _: K) -> Effect {{ Effect }} }}
    #[derive(Clone, Copy)] pub struct Handle<T>(::std::marker::PhantomData<T>);
    impl<T> Handle<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Atom<T>(::std::marker::PhantomData<T>);
    impl<T> Atom<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Form<T>(::std::marker::PhantomData<T>);
    impl<T> Form<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct CssClass(&'static str);
    impl CssClass {{ pub const fn new(name: &'static str) -> Self {{ Self(name) }} pub const fn as_str(self) -> &'static str {{ self.0 }} }}
    #[derive(Clone, Copy)] pub struct ComponentRef(&'static str);
    impl ComponentRef {{ pub const fn new(name: &'static str) -> Self {{ Self(name) }} pub const fn as_str(self) -> &'static str {{ self.0 }} }}
    pub struct SafeHtml(String);
    impl SafeHtml {{ pub fn trusted(html: impl Into<String>) -> Self {{ Self(html.into()) }} }}
    pub struct Html(SafeHtml);
    impl ::std::convert::From<Html> for SafeHtml {{ fn from(value: Html) -> Self {{ value.0 }} }}
    impl ::std::convert::AsRef<str> for Html {{ fn as_ref(&self) -> &str {{ "" }} }}
    pub mod __private {{ pub fn html_trusted(html: impl Into<String>) -> super::Html {{ super::Html(super::SafeHtml::trusted(html)) }} }}
    pub mod advanced {{ pub use super::*; }}
    pub struct FormContract {{ pub fields: &'static [FormField] }}
    pub struct FormField {{ pub name: &'static str, pub kind: FormControlKind, pub required: bool }}
    pub enum FormControlKind {{ Text, Number {{ min: Option<&'static str>, max: Option<&'static str>, step: Option<&'static str> }}, Checkbox, Radio, Select {{ multiple: bool }}, TextArea, File, Hidden, Submit, Other {{ tag: &'static str, input_type: Option<&'static str> }} }}
}}
mod hemplate {{
    pub trait Hemplate {{ fn render_into(&self, out: &mut String) -> Result<(), ()>; }}
}}
{generated}
fn main() {{
    assert_eq!(classes::drag_handle.as_str(), "drag-handle");
    assert_eq!(card::classes::is_active.as_str(), "is-active");
    assert_eq!(panel::classes::panel_shell.as_str(), "panel-shell");
}}
"###,
        );
        let source_path = base.join("classes.rs");
        let bin_path = base.join("classes-bin");
        std::fs::write(&source_path, source).unwrap();
        let status = std::process::Command::new("rustc")
            .arg(&source_path)
            .arg("-o")
            .arg(&bin_path)
            .status()
            .unwrap();
        assert!(status.success());
        let status = std::process::Command::new(&bin_path).status().unwrap();
        assert!(status.success());

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn rejects_hemx_resources_inside_unkeyed_for() {
        // req: scope/001
        for (case, template, resource) in [
            (
                "slot",
                r#"<template h-for="todo in &self.todos"><li data-hemx-slot="todo_row">{+ todo.title +}</li></template>"#,
                "data-hemx-slot=\"todo_row\"",
            ),
            (
                "slot_data_key",
                r#"<template h-for="todo in &self.todos"><li data-hemx-slot="todo_row" +data-key="todo.id">{+ todo.title +}</li></template>"#,
                "data-hemx-slot=\"todo_row\"",
            ),
            (
                "handle",
                r#"<template h-for="todo in &self.todos"><button data-hemx-handle="delete">Delete</button></template>"#,
                "data-hemx-handle=\"delete\"",
            ),
        ] {
            let base = test_dir(&format!("hemx-build-unkeyed-for-{case}-test"));
            let templates = base.join("templates");
            let out = base.join("out");
            let _ = std::fs::remove_dir_all(&base);
            std::fs::create_dir_all(&templates).unwrap();
            std::fs::write(templates.join("todo.heml"), template).unwrap();

            let err = app()
                .template_dir(&templates)
                .out_dir(&out)
                .run()
                .unwrap_err();
            assert!(err.to_string().contains("inside an h-for without h-key"));
            assert!(err.to_string().contains(resource));

            let _ = std::fs::remove_dir_all(&base);
        }
    }

    #[test]
    fn rejects_selector_style_targeting_attrs() {
        // req: locality/001 req: locality/002 req: htmx_equivalents/003
        for (case, template, attr) in [
            (
                "hemx-target",
                r##"<button data-hemx-handle="save" data-hemx-target="#row">Save</button>"##,
                "data-hemx-target",
            ),
            (
                "hemx-select",
                r##"<button data-hemx-handle="save" data-hemx-select="closest tr">Save</button>"##,
                "data-hemx-select",
            ),
        ] {
            let base = test_dir(&format!("hemx-build-selector-target-{case}-test"));
            let templates = base.join("templates");
            let out = base.join("out");
            let _ = std::fs::remove_dir_all(&base);
            std::fs::create_dir_all(&templates).unwrap();
            std::fs::write(templates.join("target.heml"), template).unwrap();

            let err = app()
                .template_dir(&templates)
                .out_dir(&out)
                .run()
                .unwrap_err();
            assert!(
                err.to_string().contains(attr),
                "missing attr in diagnostic: {err}"
            );
            assert!(
                err.to_string().contains("selector-style targeting"),
                "missing selector diagnostic: {err}"
            );
            assert!(
                err.to_string().contains("data-hemx-slot"),
                "missing suggested slot fix: {err}"
            );

            let _ = std::fs::remove_dir_all(&base);
        }
    }

    #[test]
    fn rejects_unknown_hemx_authoring_attrs() {
        // req: convention/009 req: diagnostics/002
        let base = test_dir("hemx-build-unknown-hemx-attr-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("typo.heml"),
            r#"<button data-hemx-handle="save" data-hemx-pendig-class="busy">Save</button>"#,
        )
        .unwrap();

        let err = app()
            .template_dir(&templates)
            .out_dir(&out)
            .run()
            .unwrap_err();
        assert!(
            err.to_string().contains("data-hemx-pendig-class"),
            "missing attr in diagnostic: {err}"
        );
        assert!(
            err.to_string().contains("unknown hemx attribute"),
            "missing unknown-attr diagnostic: {err}"
        );
        assert!(
            err.to_string().contains("check the spelling"),
            "missing spelling guidance: {err}"
        );
        assert!(
            err.to_string().contains("non-hemx data-*"),
            "missing app metadata guidance: {err}"
        );

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn rejects_invalid_static_hemx_convention_values() {
        // req: convention/002 req: convention/003 req: convention/004 req: convention/005 req: convention/006 req: diagnostics/002
        for (case, template, attr, guidance) in [
            (
                "policy",
                r#"<button data-hemx-handle="save" data-hemx-policy="newest">Save</button>"#,
                "data-hemx-policy",
                "latest",
            ),
            (
                "debounce",
                r#"<button data-hemx-handle="save" data-hemx-debounce="soon">Save</button>"#,
                "data-hemx-debounce",
                "250ms",
            ),
            (
                "every",
                r#"<button data-hemx-handle="save" data-hemx-every="1sec">Save</button>"#,
                "data-hemx-every",
                "1s",
            ),
            (
                "event",
                r#"<button data-hemx-handle="save" data-hemx-on="keydown">Save</button>"#,
                "data-hemx-on",
                "click",
            ),
            (
                "empty-event",
                r#"<button data-hemx-handle="save" data-hemx-on="">Save</button>"#,
                "data-hemx-on",
                "click",
            ),
            (
                "empty-confirm",
                r#"<button data-hemx-handle="delete" data-hemx-confirm="">Delete</button>"#,
                "data-hemx-confirm",
                "non-empty",
            ),
            (
                "empty-sse",
                r#"<section data-hemx-root="notifications" data-hemx-sse=""></section>"#,
                "data-hemx-sse",
                "same-origin SSE URL",
            ),
        ] {
            let base = test_dir(&format!("hemx-build-invalid-convention-{case}-test"));
            let templates = base.join("templates");
            let out = base.join("out");
            let _ = std::fs::remove_dir_all(&base);
            std::fs::create_dir_all(&templates).unwrap();
            std::fs::write(templates.join("invalid.heml"), template).unwrap();

            let err = app()
                .template_dir(&templates)
                .out_dir(&out)
                .run()
                .unwrap_err();
            assert!(
                err.to_string().contains(attr),
                "missing attr in diagnostic: {err}"
            );
            assert!(
                err.to_string().contains("invalid"),
                "missing invalid-value diagnostic: {err}"
            );
            assert!(
                err.to_string().contains(guidance),
                "missing fix guidance {guidance:?}: {err}"
            );

            let _ = std::fs::remove_dir_all(&base);
        }
    }

    #[test]
    fn rejects_invalid_hemx_attr_placement() {
        // req: page_swap/001 req: page_swap/007 req: push/006 req: diagnostics/002
        for (case, template, attr, guidance) in [
            (
                "nav-button",
                r#"<button data-hemx-nav="" data-hemx-handle="go">Go</button>"#,
                "data-hemx-nav",
                "<a href=...>",
            ),
            (
                "nav-missing-href",
                r#"<a data-hemx-nav="">Docs</a>"#,
                "data-hemx-nav",
                "<a href=...>",
            ),
            (
                "nav-empty-href",
                r#"<a href="" data-hemx-nav="">Docs</a>"#,
                "data-hemx-nav",
                "<a href=...>",
            ),
            (
                "boost-anchor",
                r#"<a href="/docs" data-hemx-boost="">Docs</a>"#,
                "data-hemx-boost",
                "data-hemx-nav",
            ),
            (
                "boost-form",
                r#"<form data-hemx-boost=""><input name="q"></form>"#,
                "data-hemx-boost",
                "data-hemx-handle",
            ),
            (
                "sse-child",
                r#"<section data-hemx-root="feed"><div data-hemx-sse="/events"></div></section>"#,
                "data-hemx-sse",
                "data-hemx-root",
            ),
        ] {
            let base = test_dir(&format!("hemx-build-invalid-placement-{case}-test"));
            let templates = base.join("templates");
            let out = base.join("out");
            let _ = std::fs::remove_dir_all(&base);
            std::fs::create_dir_all(&templates).unwrap();
            std::fs::write(templates.join("placement.heml"), template).unwrap();

            let err = app()
                .template_dir(&templates)
                .out_dir(&out)
                .run()
                .unwrap_err();
            assert!(
                err.to_string().contains(attr),
                "missing attr in diagnostic: {err}"
            );
            assert!(
                err.to_string().contains("invalid"),
                "missing invalid-placement diagnostic: {err}"
            );
            assert!(
                err.to_string().contains(guidance),
                "missing placement guidance {guidance:?}: {err}"
            );

            let _ = std::fs::remove_dir_all(&base);
        }
    }

    #[test]
    fn generated_lowering_injects_progressive_form_handle_and_key() {
        // req: form/002, req: wire/001
        let base = test_dir("hemx-build-lowering-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("todo.heml"),
            r#"<form data-hemx-handle="create"><input name="title"></form><li data-hemx-slot="row" data-hemx-key="7"></li>"#,
        )
        .unwrap();

        app().template_dir(&templates).out_dir(&out).run().unwrap();
        let generated = std::fs::read_to_string(out.join("hemx.generated.rs")).unwrap();
        assert!(generated.contains("fn __hemx_lower_html"));
        let source = format!(
            r###"
#![allow(dead_code)]
mod hemx {{
    #[derive(Clone, Copy)] pub struct BuildFingerprint;
    impl BuildFingerprint {{ pub const fn from_parts(_: &[u32]) -> Self {{ Self }} }}
    pub struct Effect;
    #[derive(Clone, Copy)] pub struct ResourceId;
    pub trait IntoEffect {{}}
    impl IntoEffect for Effect {{}}
    pub trait GeneratedTarget {{ fn __hemx_resource_id(self) -> ResourceId; }}
    pub trait KeyedPartial {{ fn hemx_key(&self) -> String; }}
    #[derive(Clone, Copy)] pub struct Slot<T>(::std::marker::PhantomData<T>);
    impl<T> Slot<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} pub const fn id(self) -> ResourceId {{ ResourceId }} pub fn html(self, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn text(self, _: impl ::std::string::ToString) -> Effect {{ Effect }} }}
    #[derive(Clone, Copy)] pub struct KeyedSlot<K, T>(::std::marker::PhantomData<(K, T)>);
    impl<K, T> KeyedSlot<K, T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} pub const fn id(self) -> ResourceId {{ ResourceId }} pub fn append_html(self, _: K, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn prepend_html(self, _: K, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn replace_html(self, _: K, _: impl ::std::convert::Into<SafeHtml>) -> Effect {{ Effect }} pub fn remove(self, _: K) -> Effect {{ Effect }} }}
    #[derive(Clone, Copy)] pub struct Handle<T>(::std::marker::PhantomData<T>);
    impl<T> Handle<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Atom<T>(::std::marker::PhantomData<T>);
    impl<T> Atom<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Form<T>(::std::marker::PhantomData<T>);
    impl<T> Form<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct ComponentRef(&'static str);
    impl ComponentRef {{ pub const fn new(name: &'static str) -> Self {{ Self(name) }} pub const fn as_str(self) -> &'static str {{ self.0 }} }}
    pub struct SafeHtml(String);
    impl SafeHtml {{ pub fn trusted(html: impl Into<String>) -> Self {{ Self(html.into()) }} }}
    pub struct Html(SafeHtml);
    impl ::std::convert::From<Html> for SafeHtml {{ fn from(value: Html) -> Self {{ value.0 }} }}
    impl ::std::convert::AsRef<str> for Html {{ fn as_ref(&self) -> &str {{ "" }} }}
    pub mod __private {{ pub fn html_trusted(html: impl Into<String>) -> super::Html {{ super::Html(super::SafeHtml::trusted(html)) }} }}
    pub mod advanced {{ pub use super::*; }}
    pub struct FormContract {{ pub fields: &'static [FormField] }}
    pub struct FormField {{ pub name: &'static str, pub kind: FormControlKind, pub required: bool }}
    pub enum FormControlKind {{ Text, Number {{ min: Option<&'static str>, max: Option<&'static str>, step: Option<&'static str> }}, Checkbox, Radio, Select {{ multiple: bool }}, TextArea, File, Hidden, Submit, Other {{ tag: &'static str, input_type: Option<&'static str> }} }}
}}
mod hemplate {{
    pub trait Hemplate {{ fn render_into(&self, out: &mut String) -> Result<(), ()>; }}
}}
{generated}
fn main() {{
    let html = todo::lower_html(r#"<form data-hemx-handle="create"><input name="title"></form><li data-hemx-slot="row" data-hemx-key="7"></li>"#);
    assert!(html.contains(r#"data-hid="#));
    assert!(html.contains(r#"name="__h""#));
    assert!(html.contains(r#"data-key="7""#));
    assert!(!html.contains("data-hemx-key"));
}}
"###,
        );
        let source_path = base.join("lowering.rs");
        let bin_path = base.join("lowering-bin");
        std::fs::write(&source_path, source).unwrap();
        let status = std::process::Command::new("rustc")
            .arg(&source_path)
            .arg("-o")
            .arg(&bin_path)
            .status()
            .unwrap();
        assert!(status.success());
        let status = std::process::Command::new(&bin_path).status().unwrap();
        assert!(status.success());

        let _ = std::fs::remove_dir_all(&base);
    }

    fn test_dir(prefix: &str) -> PathBuf {
        std::env::temp_dir().join(format!("{prefix}-{}", std::process::id()))
    }
}