[clang] [clang] Fix unresolved overloaded conversion function reference (PR #230806)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ivy Xu (IvyXu420)

<details>
<summary>Changes</summary>

According to [C++ [over.over]p5](https://eel.is/c++draft/over.over#<!-- -->5):
> [...] If more than one function in the set remains, all function
> template specializations in the set are eliminated if the set also
> contains a function that is not a function template specialization. [...]

However, in `Sema::resolveAddressOfSingleOverloadCandidate`, this part was missed, causing `IsResultAmbiguous`
to be set to true and an error to be emitted wrongly.

Fixes #<!-- -->230682.

AI was used to help understand the code.



---
Full diff: https://github.com/llvm/llvm-project/pull/230806.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.md (+3) 
- (modified) clang/lib/Sema/SemaOverload.cpp (+12) 
- (modified) clang/test/CXX/over/over.over/p2-resolve-single-template-id.cpp (+12) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 77a1e73bc8af6..d676983e42ce5 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -931,6 +931,9 @@ features cannot lower the translation-unit ABI level;
   constrained placeholder type (such as `C auto`) whose default argument
   contains a lambda. (#GH230539)
 
+- Fixed a bug where Clang failed to resolve a reference to an overloaded
+  conversion function when one of the overloads was non-template. (#GH230682)
+
 #### Bug Fixes to AST Handling
 
 - Fixed a non-deterministic ordering of unused local typedefs that made
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 62b6ad8ffb564..2ca12f7a172e7 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -14375,6 +14375,18 @@ Sema::resolveAddressOfSingleOverloadCandidate(Expr *E, DeclAccessPair &Pair) {
       // FD has the same CUDA preference than Result. Continue to check
       // constraints.
 
+      // C++ [over.over]p5:
+      //    [...] If more than one function in the set remains, all function
+      //    template specializations in the set are eliminated if the set also
+      //    contains a function that is not a function template specialization.
+      //    [...]
+      if (Result->isFunctionTemplateSpecialization() !=
+          FD->isFunctionTemplateSpecialization()) {
+        if (!FD->isFunctionTemplateSpecialization())
+          FoundBetter();
+        continue;
+      }
+
       // C++ [over.over]p5:
       //    [...] Any given non-template function F0 is eliminated if the set
       //    contains a second non-template function that is more
diff --git a/clang/test/CXX/over/over.over/p2-resolve-single-template-id.cpp b/clang/test/CXX/over/over.over/p2-resolve-single-template-id.cpp
index e538b99a1eb0b..260bbd5a8c185 100644
--- a/clang/test/CXX/over/over.over/p2-resolve-single-template-id.cpp
+++ b/clang/test/CXX/over/over.over/p2-resolve-single-template-id.cpp
@@ -189,3 +189,15 @@ namespace member_pointers {
     { bool b = &s.h<int>; } // expected-error {{cannot form member pointer of type 'bool' without '&' and class name}}
   }
 }
+
+namespace conversion_functions {
+  struct S {
+	operator int();
+
+	template<typename T> operator T();
+};
+
+  void test() {
+    &S::operator int; // expected-warning {{expression result unused}}
+  }
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/230806