feat(derive): check form model structure

Add #[slhx::form] for user-authored form models, emit form field metadata into slhx.syms, and require form handlers to accept models that passed generated field compatibility checks.

req: form/001

req: form/004

req: form/006

req: codegen/004

slhx-derive/tests/compile_fail.rs

@@ -218,6 +218,225 @@ fn show(todo_id: String) -> impl slhx::IntoEffect {
     );
 }
 
+#[test]
+fn form_struct_rejects_missing_generated_field() {
+    // req: form/001 req: form/004 req: form/006 req: test/003
+    let fixture = Fixture::new("slhx-derive-form-struct-missing-field-fail");
+    fixture.write(
+        "Cargo.toml",
+        &format!(
+            r#"[package]
+name = "slhx-derive-form-struct-missing-field-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\nform\ttemplates/app.heml::new_todo\tnew_todo\t1\nform_field\tnew_todo\ttitle\ttrue\tfalse\n",
+    )
+    .unwrap();
+}
+"#,
+    );
+    fixture.write(
+        "src/lib.rs",
+        r#"#[slhx::form("new_todo")]
+struct CreateTodo {}
+"#,
+    );
+
+    let output = check_fixture(&fixture);
+
+    assert!(!output.status.success(), "fixture unexpectedly compiled");
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("slhx form `new_todo` is missing field `title` for form control `title`"),
+        "missing form field diagnostic in stderr:\n{stderr}"
+    );
+}
+
+#[test]
+fn form_struct_rejects_wrong_optionality_and_multiplicity() {
+    // req: form/004 req: form/006 req: test/003
+    let fixture = Fixture::new("slhx-derive-form-struct-shape-fail");
+    fixture.write(
+        "Cargo.toml",
+        &format!(
+            r#"[package]
+name = "slhx-derive-form-struct-shape-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\nform\ttemplates/app.heml::profile\tprofile\t1\nform_field\tprofile\ttitle\ttrue\tfalse\nform_field\tprofile\tlabels\tfalse\ttrue\n",
+    )
+    .unwrap();
+}
+"#,
+    );
+    fixture.write(
+        "src/lib.rs",
+        r#"#[slhx::form("profile")]
+struct Profile {
+    title: Option<String>,
+    labels: Option<String>,
+}
+"#,
+    );
+
+    let output = check_fixture(&fixture);
+
+    assert!(!output.status.success(), "fixture unexpectedly compiled");
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("field `title` is required in HTML and must not be Option<_>"),
+        "missing required-field diagnostic in stderr:\n{stderr}"
+    );
+    assert!(
+        stderr.contains("field `labels` accepts multiple values and must be Vec<_>"),
+        "missing multiplicity diagnostic in stderr:\n{stderr}"
+    );
+}
+
+#[test]
+fn form_handle_accepts_checked_form_model() {
+    // req: form/001 req: form/004 req: form/006
+    let fixture = Fixture::new("slhx-derive-form-handler-checked-model-pass");
+    fixture.write(
+        "Cargo.toml",
+        &format!(
+            r#"[package]
+name = "slhx-derive-form-handler-checked-model-pass"
+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::create\tcreate\t1\nhandle_form\tcreate\tnew_todo\nform\ttemplates/app.heml::new_todo\tnew_todo\t1\nform_field\tnew_todo\ttitle\ttrue\tfalse\n",
+    )
+    .unwrap();
+}
+"#,
+    );
+    fixture.write(
+        "src/lib.rs",
+        r#"#[slhx::form("new_todo")]
+struct CreateTodo {
+    title: String,
+}
+
+#[slhx::handler]
+fn create(_form: slhx::Form<CreateTodo>) -> impl slhx::IntoEffect {
+    slhx::event("created", "")
+}
+"#,
+    );
+
+    let output = check_fixture(&fixture);
+
+    assert!(
+        output.status.success(),
+        "fixture failed to compile:\n{}",
+        String::from_utf8_lossy(&output.stderr)
+    );
+}
+
+#[test]
+fn form_handle_requires_checked_form_model() {
+    // req: form/001 req: form/004 req: form/006 req: test/003
+    let fixture = Fixture::new("slhx-derive-form-handler-unchecked-model-fail");
+    fixture.write(
+        "Cargo.toml",
+        &format!(
+            r#"[package]
+name = "slhx-derive-form-handler-unchecked-model-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::create\tcreate\t1\nhandle_form\tcreate\tnew_todo\n",
+    )
+    .unwrap();
+}
+"#,
+    );
+    fixture.write(
+        "src/lib.rs",
+        r#"struct CreateTodo {
+    title: String,
+}
+
+#[slhx::handler]
+fn create(_form: slhx::Form<CreateTodo>) -> impl slhx::IntoEffect {
+    slhx::event("created", "")
+}
+"#,
+    );
+
+    let output = check_fixture(&fixture);
+
+    assert!(!output.status.success(), "fixture unexpectedly compiled");
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("CreateTodo: FormModel") || stderr.contains("CreateTodo: slhx::FormModel"),
+        "missing checked form model diagnostic in stderr:\n{stderr}"
+    );
+}
+
 #[test]
 fn form_handle_requires_form_parameter() {
     // req: form/004 req: form/006 req: test/003