Keep track of parse errors in mods and don't emit resolve errors for paths involving them

When we expand a `mod foo;` and parse `foo.rs`, we now track whether that file had an unrecovered parse error that reached the end of the file. If so, we keep that information around. When resolving a path like `foo::bar`, we do not emit any errors for "`bar` not found in `foo`", as we know that the parse error might have caused `bar` to not be parsed and accounted for.

When this happens in an existing project, every path referencing `foo` would be an irrelevant compile error. Instead, we now skip emitting anything until `foo.rs` is fixed. Tellingly enough, we didn't have any test for errors caused by `mod` expansion.

Fix #97734.

Author: estebank

compiler/rustc_ast/src/ast.rs

@@ -2877,7 +2877,7 @@ pub enum ModKind {
     /// or with definition outlined to a separate file `mod foo;` and already loaded from it.
     /// The inner span is from the first token past `{` to the last token until `}`,
     /// or from the first to the last token in the loaded file.
-    Loaded(ThinVec<P<Item>>, Inline, ModSpans),
+    Loaded(ThinVec<P<Item>>, Inline, ModSpans, Result<(), ErrorGuaranteed>),
     /// Module with definition outlined to a separate file `mod foo;` but not yet loaded from it.
     Unloaded,
 }

compiler/rustc_ast/src/mut_visit.rs

@@ -1212,7 +1212,12 @@ impl WalkItemKind for ItemKind {
             ItemKind::Mod(safety, mod_kind) => {
                 visit_safety(vis, safety);
                 match mod_kind {
-                    ModKind::Loaded(items, _inline, ModSpans { inner_span, inject_use_span }) => {
+                    ModKind::Loaded(
+                        items,
+                        _inline,
+                        ModSpans { inner_span, inject_use_span },
+                        _,
+                    ) => {
                         items.flat_map_in_place(|item| vis.flat_map_item(item));
                         vis.visit_span(inner_span);
                         vis.visit_span(inject_use_span);

compiler/rustc_ast/src/visit.rs

@@ -380,7 +380,7 @@ impl WalkItemKind for ItemKind {
                 try_visit!(visitor.visit_fn(kind, span, id));
             }
             ItemKind::Mod(_unsafety, mod_kind) => match mod_kind {
-                ModKind::Loaded(items, _inline, _inner_span) => {
+                ModKind::Loaded(items, _inline, _inner_span, _) => {
                     walk_list!(visitor, visit_item, items);
                 }
                 ModKind::Unloaded => {}

compiler/rustc_ast_lowering/src/item.rs

@@ -238,7 +238,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 })
             }
             ItemKind::Mod(_, mod_kind) => match mod_kind {
-                ModKind::Loaded(items, _, spans) => {
+                ModKind::Loaded(items, _, spans, _) => {
                     hir::ItemKind::Mod(self.lower_mod(items, spans))
                 }
                 ModKind::Unloaded => panic!("`mod` items should have been loaded by now"),

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1029,7 +1029,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     self.dcx().emit_err(errors::UnsafeItem { span, kind: "module" });
                 }
                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
-                if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _))
+                if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _, _))
                     && !attr::contains_name(&item.attrs, sym::path)
                 {
                     self.check_mod_file_item_asciionly(item.ident);

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -141,8 +141,10 @@ impl<'a> MutVisitor for TestHarnessGenerator<'a> {
 
         // We don't want to recurse into anything other than mods, since
         // mods or tests inside of functions will break things
-        if let ast::ItemKind::Mod(_, ModKind::Loaded(.., ast::ModSpans { inner_span: span, .. })) =
-            item.kind
+        if let ast::ItemKind::Mod(
+            _,
+            ModKind::Loaded(.., ast::ModSpans { inner_span: span, .. }, _),
+        ) = item.kind
         {
             let prev_tests = mem::take(&mut self.tests);
             walk_item_kind(

compiler/rustc_expand/src/expand.rs

@@ -723,7 +723,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                     item_inner.kind,
                                     ItemKind::Mod(
                                         _,
-                                        ModKind::Unloaded | ModKind::Loaded(_, Inline::No, _),
+                                        ModKind::Unloaded | ModKind::Loaded(_, Inline::No, _, _),
                                     )
                                 ) =>
                         {
@@ -889,7 +889,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             fn visit_item(&mut self, item: &'ast ast::Item) {
                 match &item.kind {
                     ItemKind::Mod(_, mod_kind)
-                        if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _)) =>
+                        if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _, _)) =>
                     {
                         feature_err(
                             self.sess,
@@ -1195,7 +1195,7 @@ impl InvocationCollectorNode for P<ast::Item> {
 
         let ecx = &mut collector.cx;
         let (file_path, dir_path, dir_ownership) = match mod_kind {
-            ModKind::Loaded(_, inline, _) => {
+            ModKind::Loaded(_, inline, _, _) => {
                 // Inline `mod foo { ... }`, but we still need to push directories.
                 let (dir_path, dir_ownership) = mod_dir_path(
                     ecx.sess,
@@ -1217,15 +1217,21 @@ impl InvocationCollectorNode for P<ast::Item> {
             ModKind::Unloaded => {
                 // We have an outline `mod foo;` so we need to parse the file.
                 let old_attrs_len = attrs.len();
-                let ParsedExternalMod { items, spans, file_path, dir_path, dir_ownership } =
-                    parse_external_mod(
-                        ecx.sess,
-                        ident,
-                        span,
-                        &ecx.current_expansion.module,
-                        ecx.current_expansion.dir_ownership,
-                        &mut attrs,
-                    );
+                let ParsedExternalMod {
+                    items,
+                    spans,
+                    file_path,
+                    dir_path,
+                    dir_ownership,
+                    had_parse_error,
+                } = parse_external_mod(
+                    ecx.sess,
+                    ident,
+                    span,
+                    &ecx.current_expansion.module,
+                    ecx.current_expansion.dir_ownership,
+                    &mut attrs,
+                );
 
                 if let Some(lint_store) = ecx.lint_store {
                     lint_store.pre_expansion_lint(
@@ -1239,7 +1245,7 @@ impl InvocationCollectorNode for P<ast::Item> {
                     );
                 }
 
-                *mod_kind = ModKind::Loaded(items, Inline::No, spans);
+                *mod_kind = ModKind::Loaded(items, Inline::No, spans, had_parse_error);
                 node.attrs = attrs;
                 if node.attrs.len() > old_attrs_len {
                     // If we loaded an out-of-line module and added some inner attributes,

compiler/rustc_expand/src/module.rs

@@ -37,6 +37,7 @@ pub(crate) struct ParsedExternalMod {
     pub file_path: PathBuf,
     pub dir_path: PathBuf,
     pub dir_ownership: DirOwnership,
+    pub had_parse_error: Result<(), ErrorGuaranteed>,
 }
 
 pub enum ModError<'a> {
@@ -74,14 +75,17 @@ pub(crate) fn parse_external_mod(
         attrs.extend(inner_attrs);
         (items, inner_span, mp.file_path)
     };
+
     // (1) ...instead, we return a dummy module.
-    let (items, spans, file_path) =
-        result.map_err(|err| err.report(sess, span)).unwrap_or_default();
+    let ((items, spans, file_path), had_parse_error) = match result {
+        Err(err) => (Default::default(), Err(err.report(sess, span))),
+        Ok(result) => (result, Ok(())),
+    };
 
     // Extract the directory path for submodules of the module.
     let dir_path = file_path.parent().unwrap_or(&file_path).to_owned();
 
-    ParsedExternalMod { items, spans, file_path, dir_path, dir_ownership }
+    ParsedExternalMod { items, spans, file_path, dir_path, dir_ownership, had_parse_error }
 }
 
 pub(crate) fn mod_dir_path(

compiler/rustc_lint/src/builtin.rs

@@ -3038,7 +3038,7 @@ impl EarlyLintPass for SpecialModuleName {
         for item in &krate.items {
             if let ast::ItemKind::Mod(
                 _,
-                ast::ModKind::Unloaded | ast::ModKind::Loaded(_, ast::Inline::No, _),
+                ast::ModKind::Unloaded | ast::ModKind::Loaded(_, ast::Inline::No, _, _),
             ) = item.kind
             {
                 if item.attrs.iter().any(|a| a.has_name(sym::path)) {

compiler/rustc_parse/src/parser/item.rs

@@ -45,7 +45,7 @@ impl<'a> Parser<'a> {
             let (inner_attrs, items, inner_span) =
                 self.parse_mod(&token::CloseDelim(Delimiter::Brace))?;
             attrs.extend(inner_attrs);
-            ModKind::Loaded(items, Inline::Yes, inner_span)
+            ModKind::Loaded(items, Inline::Yes, inner_span, Ok(()))
         };
         Ok((id, ItemKind::Mod(safety, mod_kind)))
     }