Merge #7970

7970: Fix incorrect diagnostics for failing built in macros r=jonas-schievink a=brandondong

**Reproduction:**
1. Use a built in macro in such a way that rust-analyzer fails to expand it. For example:

**lib.rs**
```
include!("<valid file but without a .rs extension so it is not indexed by rust-analyzer>");
```
2. rust-analyzer highlights the macro call and says the macro itself cannot be resolved even though include! is in the standard library (unresolved-macro-call diagnostic).
3. No macro-error diagnostic is raised.

**Root cause for incorrect unresolved-macro-call diagnostic:**
1. collector:collect_macro_call is able to resolve include! in legacy scope but the expansion fails. Therefore, it's pushed into unexpanded_macros to be retried with module scope.
2. include! fails at the resolution step in collector:resolve_macros now that it's using module scope. Therefore, it's retained in unexpanded_macros.
3. Finally, collector:finish tries resolving the remaining unexpanded macros but only with module scope. include! again fails at the resolution step so a diagnostic is created.

**Root cause for missing macro-error diagnostic:**
1. In collector:resolve_macros, directive.legacy is None since eager expansion failed in collector:collect_macro_call. The macro_call_as_call_id fails to resolve since we're retrying in module scope. Therefore, collect_macro_expansion is not called for the macro and no macro-error diagnostic is generated.

**Fix:**
- In collector:collect_macro_call, do not add failing built-in macros to the unexpanded_macros list and immediately raise the macro-error diagnostic. This is in contrast to lazy macros which are resolved in collector::resolve_macros and later expanded in collect_macro_expansion where a macro-error diagnostic may be raised.

Co-authored-by: Brandon <[email protected]>
Co-authored-by: brandondong <[email protected]>

2 files changed, 68 insertions, 10 deletions

diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index 9ed48c506..81cf652b0 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -13,7 +13,7 @@ use hir_expand::{
     builtin_macro::find_builtin_macro,
     name::{AsName, Name},
     proc_macro::ProcMacroExpander,
-    HirFileId, MacroCallId, MacroDefId, MacroDefKind,
+    HirFileId, MacroCallId, MacroCallKind, MacroDefId, MacroDefKind,
 };
 use hir_expand::{InFile, MacroCallLoc};
 use rustc_hash::{FxHashMap, FxHashSet};
@@ -1455,7 +1455,8 @@ impl ModCollector<'_, '_> {
         let mut ast_id = AstIdWithPath::new(self.file_id, mac.ast_id, mac.path.clone());
 
         // Case 1: try to resolve in legacy scope and expand macro_rules
-        if let Ok(Ok(macro_call_id)) = macro_call_as_call_id(
+        let mut error = None;
+        match macro_call_as_call_id(
             &ast_id,
             self.def_collector.db,
             self.def_collector.def_map.krate,
@@ -1468,16 +1469,28 @@ impl ModCollector<'_, '_> {
                     )
                 })
             },
-            &mut |_err| (),
+            &mut |err| error = Some(err),
         ) {
-            self.def_collector.unexpanded_macros.push(MacroDirective {
-                module_id: self.module_id,
-                ast_id,
-                legacy: Some(macro_call_id),
-                depth: self.macro_depth + 1,
-            });
+            Ok(Ok(macro_call_id)) => {
+                self.def_collector.unexpanded_macros.push(MacroDirective {
+                    module_id: self.module_id,
+                    ast_id,
+                    legacy: Some(macro_call_id),
+                    depth: self.macro_depth + 1,
+                });
 
-            return;
+                return;
+            }
+            Ok(Err(_)) => {
+                // Built-in macro failed eager expansion.
+                self.def_collector.def_map.diagnostics.push(DefDiagnostic::macro_error(
+                    self.module_id,
+                    MacroCallKind::FnLike(ast_id.ast_id),
+                    error.unwrap().to_string(),
+                ));
+                return;
+            }
+            Err(UnresolvedMacro) => (),
         }
 
         // Case 2: resolve in module scope, expand during name resolution.
diff --git a/crates/hir_def/src/nameres/tests/diagnostics.rs b/crates/hir_def/src/nameres/tests/diagnostics.rs
index 1b8e885b0..c22ef46fd 100644
--- a/crates/hir_def/src/nameres/tests/diagnostics.rs
+++ b/crates/hir_def/src/nameres/tests/diagnostics.rs
@@ -155,3 +155,48 @@ fn inactive_via_cfg_attr() {
         "#,
     );
 }
+
+#[test]
+fn unresolved_legacy_scope_macro() {
+    check_diagnostics(
+        r#"
+        //- /lib.rs
+          macro_rules! m { () => {} }
+
+          m!();
+          m2!();
+        //^^^^^^ unresolved macro call
+        "#,
+    );
+}
+
+#[test]
+fn unresolved_module_scope_macro() {
+    check_diagnostics(
+        r#"
+        //- /lib.rs
+          mod mac {
+            #[macro_export]
+            macro_rules! m { () => {} }
+          }
+
+          self::m!();
+          self::m2!();
+        //^^^^^^^^^^^^ unresolved macro call
+        "#,
+    );
+}
+
+#[test]
+fn builtin_macro_fails_expansion() {
+    check_diagnostics(
+        r#"
+        //- /lib.rs
+          #[rustc_builtin_macro]
+          macro_rules! include { () => {} }
+
+          include!("doesntexist");
+        //^^^^^^^^^^^^^^^^^^^^^^^^ could not convert tokens
+        "#,
+    );
+}