[clang] [Clang][AST] Fix a crash on attaching doc comments (PR #78716)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Shanzhi (chenshanzhi)

<details>
<summary>Changes</summary>

This crash is basically caused by calling
`ASTContext::getRawCommentForDeclNoCacheImp` with its input arguments `RepresentativeLocForDecl` and `CommentsInTheFile` refering to different files. A reduced reproducer is provided in this patch.

After the source locations for instantiations of funtion template are corrected in the commit 256a0b298c68b89688b80350b034daf2f7785b67, the variable `CommitsInThisFile` in the function
`ASTContext::attachCommentsToJustParsedDecls` would refer to the source file rather than the header file for implicit function template instantiation. Therefore, in the first loop in `ASTContext::attachCommentsToJustParsedDecls`, `D` should also be adjusted for relevant scenarios like the second loop.

Fixes #<!-- -->67979 #<!-- -->68524 #<!-- -->70550

---
Full diff: https://github.com/llvm/llvm-project/pull/78716.diff


2 Files Affected:

- (modified) clang/lib/AST/ASTContext.cpp (+5-1) 
- (added) clang/test/AST/ast-crash-doc-function-template.cpp (+30) 


``````````diff
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 0fc0831b221aab..3abc526efd7de6 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -498,7 +498,11 @@ void ASTContext::attachCommentsToJustParsedDecls(ArrayRef<Decl *> Decls,
     return;
 
   FileID File;
-  for (Decl *D : Decls) {
+  for (const Decl *D : Decls) {
+    if (D->isInvalidDecl())
+      continue;
+
+    D = &adjustDeclToTemplate(*D);
     SourceLocation Loc = D->getLocation();
     if (Loc.isValid()) {
       // See if there are any new comments that are not attached to a decl.
diff --git a/clang/test/AST/ast-crash-doc-function-template.cpp b/clang/test/AST/ast-crash-doc-function-template.cpp
new file mode 100644
index 00000000000000..d48eb0dbe02f01
--- /dev/null
+++ b/clang/test/AST/ast-crash-doc-function-template.cpp
@@ -0,0 +1,30 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -x c++ -Wdocumentation -fsyntax-only -ast-dump-all %t/t.cpp
+
+//--- t.h
+/// MyClass in the header file
+class MyClass {
+public:
+  template <typename T>
+  void Foo() const;
+
+  /// Bar
+  void Bar() const;
+};
+
+//--- t.cpp
+#include "t.h"
+
+/// MyClass::Bar: Foo<int>() is implicitly instantiated and called here.
+void MyClass::Bar() const {
+  Foo<int>();
+}
+
+/// MyClass::Foo
+template <typename T>
+void MyClass::Foo() const {
+}
+
+// CHECK: TranslationUnitDecl

``````````

</details>


https://github.com/llvm/llvm-project/pull/78716