Supress some lookup errors if a module contains compile_error!

The problem is that when a macro expand to `compile_error!` because
its input is malformed, the actual error message from the
`compile_error!` might be hidden in a long list of other messages about
using items that should have otherwise been generated by the macro.

So suppress error about missing items in that module.

Author: ogoffart

compiler/rustc_builtin_macros/src/compile_error.rs

@@ -22,6 +22,7 @@ pub(crate) fn expand_compile_error<'cx>(
     #[expect(rustc::diagnostic_outside_of_impl, reason = "diagnostic message is specified by user")]
     #[expect(rustc::untranslatable_diagnostic, reason = "diagnostic message is specified by user")]
     let guar = cx.dcx().span_err(sp, var.to_string());
+    cx.resolver.mark_scope_with_compile_error(cx.current_expansion.lint_node_id);
 
     ExpandResult::Ready(DummyResult::any(sp, guar))
 }

compiler/rustc_expand/src/base.rs

@@ -1200,6 +1200,10 @@ pub trait ResolverExpand {
     /// Record the name of an opaque `Ty::ImplTrait` pre-expansion so that it can be used
     /// to generate an item name later that does not reference placeholder macros.
     fn insert_impl_trait_name(&mut self, id: NodeId, name: Symbol);
+
+    /// Mark the scope as having a compile error so that error for lookup in this scope
+    /// should be suppressed
+    fn mark_scope_with_compile_error(&mut self, parent_node: NodeId);
 }
 
 pub trait LintStoreExpand {

compiler/rustc_resolve/src/ident.rs

@@ -1718,7 +1718,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         diag_metadata: Option<&DiagMetadata<'_>>,
     ) -> PathResult<'ra> {
         let mut module = None;
-        let mut module_had_parse_errors = false;
+        let mut module_had_parse_errors = !self.mods_with_parse_errors.is_empty()
+            && self.mods_with_parse_errors.contains(&parent_scope.module.nearest_parent_mod());
         let mut allow_super = true;
         let mut second_binding = None;
 

compiler/rustc_resolve/src/macros.rs

@@ -167,6 +167,12 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
         self.invocation_parents[&id].parent_def
     }
 
+    fn mark_scope_with_compile_error(&mut self, id: NodeId) {
+        if let Some(id) = self.opt_local_def_id(id) {
+            self.mods_with_parse_errors.insert(id.to_def_id());
+        }
+    }
+
     fn resolve_dollar_crates(&self) {
         hygiene::update_dollar_crate_names(|ctxt| {
             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));

tests/ui/macros/compile_error_macro-suppress-errors.rs

@@ -0,0 +1,25 @@
+mod some_module {
+    compile_error!("Error in a module"); //~ ERROR: Error in a module
+
+    fn abc() {
+        let _: self::SomeType = self::Hello::new();
+        let _: SomeType = Hello::new();
+    }
+}
+
+mod another_module {}
+
+fn main() {
+    // these errors are suppressed because of the compile_error! macro
+
+    let _ = some_module::some_function();
+    let _: some_module::SomeType = some_module::Hello::new();
+
+    // these errors are not suppressed
+
+    let _ = another_module::some_function();
+    //~^ ERROR: cannot find function `some_function` in module `another_module`
+    let _: another_module::SomeType = another_module::Hello::new();
+    //~^ ERROR: cannot find type `SomeType` in module `another_module`
+    //~^^ ERROR: failed to resolve: could not find `Hello` in `another_module`
+}

tests/ui/macros/compile_error_macro-suppress-errors.stderr

@@ -0,0 +1,28 @@
+error: Error in a module
+  --> $DIR/compile_error_macro-suppress-errors.rs:2:5
+   |
+LL |     compile_error!("Error in a module");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0433]: failed to resolve: could not find `Hello` in `another_module`
+  --> $DIR/compile_error_macro-suppress-errors.rs:22:55
+   |
+LL |     let _: another_module::SomeType = another_module::Hello::new();
+   |                                                       ^^^^^ could not find `Hello` in `another_module`
+
+error[E0425]: cannot find function `some_function` in module `another_module`
+  --> $DIR/compile_error_macro-suppress-errors.rs:20:29
+   |
+LL |     let _ = another_module::some_function();
+   |                             ^^^^^^^^^^^^^ not found in `another_module`
+
+error[E0412]: cannot find type `SomeType` in module `another_module`
+  --> $DIR/compile_error_macro-suppress-errors.rs:22:28
+   |
+LL |     let _: another_module::SomeType = another_module::Hello::new();
+   |                            ^^^^^^^^ not found in `another_module`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0412, E0425, E0433.
+For more information about an error, try `rustc --explain E0412`.