Improve entry main diagnostics

.llm/BETA_4_LANGUAGE_USABILITY.md

@@ -0,0 +1,26 @@
+# Beta 4 Language Usability
+
+## Scope
+
+This post-`1.0.0-beta.3` slice reduces friction in ordinary project use
+without changing the typed core or claiming new syntax stability.
+
+## Current Work
+
+- Improve project/workspace build and run entry diagnostics.
+- Keep the accepted entry contract unchanged: `(fn main () -> i32 ...)`.
+- Use precise diagnostic codes for missing and invalid entry `main` functions.
+
+## Acceptance Gates
+
+- `cargo test --test project_mode entry_main`
+- `cargo fmt --check`
+- `git diff --check`
+
+## Deferrals
+
+- No implicit `main` return conversions.
+- No argument-taking `main`.
+- No async, package registry, or stable ABI/layout promises.
+- Broader type aliases, match diagnostics, and destructuring remain candidate
+  follow-up items in the same language usability roadmap lane.

compiler/src/project.rs

@@ -4156,8 +4156,11 @@ fn add_entry_wrapper(
     else {
         diagnostics.push(Diagnostic::new(
             &entry_module.file,
-            "MissingImport",
+            "ProjectEntryMainMissing",
-            format!("entry module `{}` has no `main` function", manifest.entry),
+            format!(
+                "entry module `{}` has no `main` function; build/run require `(fn main () -> i32 ...)`",
+                manifest.entry
+            ),
         ));
         return;
     };
@@ -4166,8 +4169,12 @@ fn add_entry_wrapper(
         diagnostics.push(
             Diagnostic::new(
                 &entry_module.file,
-                "MissingImport",
+                "ProjectEntryMainInvalidSignature",
-                "project entry `main` must have no parameters and return `i32`",
+                format!(
+                    "project entry `main` must have signature `(fn main () -> i32 ...)`; found {} parameter(s) and return `{}`",
+                    entry_function.params.len(),
+                    entry_function.return_type
+                ),
             )
             .with_span(entry_function.span),
         );
@@ -4229,9 +4236,9 @@ fn add_workspace_entry_wrapper(
     else {
         diagnostics.push(Diagnostic::new(
             &entry_module.file,
-            "MissingImport",
+            "WorkspaceEntryMainMissing",
             format!(
-                "entry module `{}` in package `{}` has no `main` function",
+                "entry module `{}` in package `{}` has no `main` function; build/run require `(fn main () -> i32 ...)`",
                 package.manifest.entry, package.manifest.name
             ),
         ));
@@ -4242,8 +4249,12 @@ fn add_workspace_entry_wrapper(
         diagnostics.push(
             Diagnostic::new(
                 &entry_module.file,
-                "MissingImport",
+                "WorkspaceEntryMainInvalidSignature",
-                "workspace entry `main` must have no parameters and return `i32`",
+                format!(
+                    "workspace entry `main` must have signature `(fn main () -> i32 ...)`; found {} parameter(s) and return `{}`",
+                    entry_function.params.len(),
+                    entry_function.return_type
+                ),
             )
             .with_span(entry_function.span),
         );

compiler/tests/project_mode.rs

@@ -587,6 +587,68 @@ fn workspace_build_requires_one_entry_package() {
     );
 }
 
+#[test]
+fn workspace_build_reports_entry_main_contract() {
+    let missing_main = write_workspace(
+        "workspace-missing-entry-main",
+        "[workspace]\nmembers = [\"packages/app\"]\n",
+        &[WorkspacePackageSpec {
+            member: "packages/app",
+            manifest: "[package]\nname = \"app\"\nversion = \"0.1.0\"\n",
+            modules: &[("main", "(module main)\n\n(test \"ok\"\n  true)\n")],
+        }],
+    );
+    let missing_binary = unique_path("workspace-missing-entry-main-bin");
+    let missing_output = run_glagol([
+        "build".as_ref(),
+        "-o".as_ref(),
+        missing_binary.as_os_str(),
+        missing_main.as_os_str(),
+    ]);
+    assert_exit_code("workspace missing entry main", &missing_output, 1);
+    assert_stderr_contains(
+        "workspace missing entry main",
+        &missing_output,
+        "WorkspaceEntryMainMissing",
+    );
+    assert_stderr_contains(
+        "workspace missing entry main",
+        &missing_output,
+        "build/run require `(fn main () -> i32 ...)`",
+    );
+
+    let bad_signature = write_workspace(
+        "workspace-bad-entry-main",
+        "[workspace]\nmembers = [\"packages/app\"]\n",
+        &[WorkspacePackageSpec {
+            member: "packages/app",
+            manifest: "[package]\nname = \"app\"\nversion = \"0.1.0\"\n",
+            modules: &[(
+                "main",
+                "(module main)\n\n(fn main () -> string\n  \"bad\")\n",
+            )],
+        }],
+    );
+    let bad_binary = unique_path("workspace-bad-entry-main-bin");
+    let bad_output = run_glagol([
+        "build".as_ref(),
+        "-o".as_ref(),
+        bad_binary.as_os_str(),
+        bad_signature.as_os_str(),
+    ]);
+    assert_exit_code("workspace bad entry main", &bad_output, 1);
+    assert_stderr_contains(
+        "workspace bad entry main",
+        &bad_output,
+        "WorkspaceEntryMainInvalidSignature",
+    );
+    assert_stderr_contains(
+        "workspace bad entry main",
+        &bad_output,
+        "found 0 parameter(s) and return `string`",
+    );
+}
+
 #[test]
 fn workspace_package_boundaries_are_diagnostics() {
     let missing = write_workspace(
@@ -1244,7 +1306,16 @@ fn project_build_requires_entry_main_contract() {
         missing_main.as_os_str(),
     ]);
     assert_exit_code("missing entry main", &missing_output, 1);
-    assert_stderr_contains("missing entry main", &missing_output, "MissingImport");
+    assert_stderr_contains(
+        "missing entry main",
+        &missing_output,
+        "ProjectEntryMainMissing",
+    );
+    assert_stderr_contains(
+        "missing entry main",
+        &missing_output,
+        "build/run require `(fn main () -> i32 ...)`",
+    );
 
     let bad_signature = write_project(
         "bad-main-signature",
@@ -1259,7 +1330,16 @@ fn project_build_requires_entry_main_contract() {
         bad_signature.as_os_str(),
     ]);
     assert_exit_code("bad entry main signature", &bad_output, 1);
-    assert_stderr_contains("bad entry main signature", &bad_output, "MissingImport");
+    assert_stderr_contains(
+        "bad entry main signature",
+        &bad_output,
+        "ProjectEntryMainInvalidSignature",
+    );
+    assert_stderr_contains(
+        "bad entry main signature",
+        &bad_output,
+        "found 1 parameter(s) and return `i32`",
+    );
 }
 
 #[test]

docs/POST_BETA_ROADMAP.md

@@ -113,6 +113,10 @@ Candidate features:
 Why fourth: these features improve real Slovo code while keeping generics and
 traits deferred until the core has more feedback.
 
+Started on `main` after `1.0.0-beta.3`: project/workspace build and run entry
+diagnostics now use entry-specific codes and explicitly show the required
+`(fn main () -> i32 ...)` contract.
+
 ### 5. Package And Workspace Discipline
 
 Goal: make multi-package local development predictable before remote registry

docs/compiler/RELEASE_NOTES.md

@@ -10,7 +10,11 @@ integration/readiness release, not the first real beta.
 
 ## Unreleased
 
-No unreleased changes yet.
+- Project build/run entry diagnostics now use entry-specific codes:
+  `ProjectEntryMainMissing`, `ProjectEntryMainInvalidSignature`,
+  `WorkspaceEntryMainMissing`, and `WorkspaceEntryMainInvalidSignature`.
+  Messages now spell out the required `(fn main () -> i32 ...)` contract and
+  include the found parameter count and return type for invalid signatures.
 
 ## 1.0.0-beta.3