feat(derive): check generated handler params

Emit handle_param facts for handled data-* attributes and reject handlers that omit generated param arguments. Cover the generated param boundary with unit and compile-fail tests.

req: derive_handler/001

req: test/003

slhx-derive/src/lib.rs

@@ -1,7 +1,7 @@
 use proc_macro::TokenStream;
 use quote::quote;
 use std::path::PathBuf;
-use syn::{parse_macro_input, FnArg, ItemFn, ReturnType, Type};
+use syn::{parse_macro_input, FnArg, ItemFn, Pat, ReturnType, Type};
 
 #[proc_macro_attribute]
 pub fn handler(_attr: TokenStream, item: TokenStream) -> TokenStream {
@@ -57,6 +57,18 @@ pub fn handler(_attr: TokenStream, item: TokenStream) -> TokenStream {
         )
         .into();
     }
+    let missing_params = missing_handle_params(&syms_path, &name, &function);
+    if !missing_params.is_empty() {
+        let message = format!(
+            "slhx handler `{name}` is missing generated param argument(s): {}",
+            missing_params.join(", ")
+        );
+        return quote!(
+            #function
+            compile_error!(#message);
+        )
+        .into();
+    }
 
     quote!(#function).into()
 }
@@ -161,6 +173,51 @@ fn handle_requires_form(path: &PathBuf, ident: &str) -> bool {
     })
 }
 
+fn missing_handle_params(path: &PathBuf, ident: &str, function: &ItemFn) -> Vec<String> {
+    let required = handle_params(path, ident);
+    if required.is_empty() {
+        return Vec::new();
+    }
+    let args = handler_arg_names(function);
+    required
+        .into_iter()
+        .filter(|param| !args.contains(param))
+        .collect()
+}
+
+fn handle_params(path: &PathBuf, ident: &str) -> Vec<String> {
+    let Ok(syms) = std::fs::read_to_string(path) else {
+        return Vec::new();
+    };
+    syms.lines()
+        .filter_map(|line| {
+            let mut fields = line.split('\t');
+            if !matches!(fields.next(), Some("handle_param")) {
+                return None;
+            }
+            if fields.next()? != ident {
+                return None;
+            }
+            fields.next().map(ToOwned::to_owned)
+        })
+        .collect()
+}
+
+fn handler_arg_names(function: &ItemFn) -> Vec<String> {
+    function
+        .sig
+        .inputs
+        .iter()
+        .filter_map(|arg| match arg {
+            FnArg::Typed(arg) => match arg.pat.as_ref() {
+                Pat::Ident(ident) => Some(ident.ident.to_string()),
+                _ => None,
+            },
+            FnArg::Receiver(_) => None,
+        })
+        .collect()
+}
+
 fn compile_error(message: &str) -> TokenStream {
     format!("compile_error!({message:?});")
         .parse()
@@ -169,15 +226,15 @@ fn compile_error(message: &str) -> TokenStream {
 
 #[cfg(test)]
 mod tests {
-    use super::{handle_requires_form, has_form_param, has_non_unit_return, is_form_type, syms_contains_handle};
-    use syn::{parse_quote, Type};
+    use super::{handle_params, handle_requires_form, has_form_param, has_non_unit_return, is_form_type, missing_handle_params, syms_contains_handle};
+    use syn::{parse_quote, ItemFn, Type};
 
     #[test]
     fn syms_lookup_matches_handle_ident() {
         let path = std::env::temp_dir().join("slhx-derive-syms-test.syms");
         std::fs::write(
             &path,
-            "slhx-syms-v1\nslot\ttemplates/a.heml::count\tcount\t1\nhandle\ttemplates/a.heml::create\tcreate\t2\nhandle_form\tcreate\tnew_todo\n",
+            "slhx-syms-v1\nslot\ttemplates/a.heml::count\tcount\t1\nhandle\ttemplates/a.heml::create\tcreate\t2\nhandle_form\tcreate\tnew_todo\nhandle_param\tcreate\ttodo_id\n",
         )
         .unwrap();
 
@@ -185,6 +242,8 @@ mod tests {
         assert!(!syms_contains_handle(&path, "missing"));
         assert!(handle_requires_form(&path, "create"));
         assert!(!handle_requires_form(&path, "missing"));
+        assert_eq!(handle_params(&path, "create"), vec!["todo_id"]);
+        assert!(handle_params(&path, "missing").is_empty());
 
         let _ = std::fs::remove_file(path);
     }
@@ -210,4 +269,18 @@ mod tests {
         assert!(is_form_type(&real_form));
         assert!(!is_form_type(&impostor));
     }
+
+    #[test]
+    fn handler_params_match_generated_param_names() {
+        let path = std::env::temp_dir().join("slhx-derive-param-test.syms");
+        std::fs::write(&path, "slhx-syms-v1\nhandle_param\tshow\ttodo_id\nhandle_param\tshow\tmode\n")
+            .unwrap();
+        let complete: ItemFn = parse_quote!(fn show(todo_id: String, mode: String) -> impl slhx::IntoEffect { slhx::EffectBatch::default() });
+        let missing: ItemFn = parse_quote!(fn show(todo_id: String) -> impl slhx::IntoEffect { slhx::EffectBatch::default() });
+
+        assert!(missing_handle_params(&path, "show", &complete).is_empty());
+        assert_eq!(missing_handle_params(&path, "show", &missing), vec!["mode"]);
+
+        let _ = std::fs::remove_file(path);
+    }
 }

slhx-derive/tests/compile_fail.rs

@@ -111,6 +111,58 @@ fn create() -> impl slhx::IntoEffect {
     );
 }
 
+#[test]
+fn handler_requires_generated_param_arguments() {
+    // req: derive_handler/001 req: test/003
+    let fixture = Fixture::new("slhx-derive-param-handler-fail");
+    fixture.write(
+        "Cargo.toml",
+        &format!(
+            r#"[package]
+name = "slhx-derive-param-handler-fail"
+version = "0.0.0"
+edition = "2021"
+
+[lib]
+path = "src/lib.rs"
+
+[dependencies]
+slhx = {{ path = {:?} }}
+"#,
+            repo_path("slhx")
+        ),
+    );
+    fixture.write(
+        "build.rs",
+        r#"fn main() {
+    let out = std::path::PathBuf::from(std::env::var_os("OUT_DIR").unwrap());
+    std::fs::write(
+        out.join("slhx.syms"),
+        "slhx-syms-v1\nhandle\ttemplates/app.heml::show\tshow\t1\nhandle_param\tshow\ttodo_id\nhandle_param\tshow\tmode\n",
+    )
+    .unwrap();
+}
+"#,
+    );
+    fixture.write(
+        "src/lib.rs",
+        r#"#[slhx::handler]
+fn show(todo_id: String) -> impl slhx::IntoEffect {
+    slhx::EffectBatch::default()
+}
+"#,
+    );
+
+    let output = check_fixture(&fixture);
+
+    assert!(!output.status.success(), "fixture unexpectedly compiled");
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("slhx handler `show` is missing generated param argument(s): mode"),
+        "missing param diagnostic in stderr:\n{stderr}"
+    );
+}
+
 #[test]
 fn form_handle_requires_form_parameter() {
     // req: form/004 req: form/006 req: test/003