[clang] 25f76c9 - [clang] Find conversion function templates for in-class specializations (#218316)

[via cfe-commits]

Author: Kunal Dubey
Date: 2026-08-31T14:16:22+02:00
New Revision: 25f76c98fe049a506396d8c1709cc0efc7d01202

URL: https://github.com/llvm/llvm-project/commit/25f76c98fe049a506396d8c1709cc0efc7d01202
DIFF: https://github.com/llvm/llvm-project/commit/25f76c98fe049a506396d8c1709cc0efc7d01202.diff

LOG: [clang] Find conversion function templates for in-class specializations (#218316)

Allow redeclaration lookup to consider conversion function templates
allowing Clang to match an in-class specialization such as `template<>
operator int()` against a prior conversion function template
`template<class T> operator T()`.

Fixes #218261

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.md
    clang/lib/Sema/SemaLookup.cpp
    clang/test/SemaCXX/conversion-function.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 512b1d1d3be01..32ee602dc8472 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -551,6 +551,11 @@ features cannot lower the translation-unit ABI level;
   parameter that follows a parameter pack (e.g.
   `template <typename... T> S::S(T..., int = 10) {}`).  (#GH216211)
 
+- Allow redeclaration lookup to consider conversion function templates, allowing
+  Clang to match an in-class specialization such as `template<> operator int()`
+  against a prior conversion function template `template<class T> operator T()`.
+  (#GH218261)
+
 - Fixed an assertion when an ill-formed qualified member function definition
   inside a union caused the union to be treated as a polymorphic class.
   (#GH213854)

diff  --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 43419c46dd2bf..319c228bad3b0 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -1158,7 +1158,7 @@ static bool LookupDirect(Sema &S, LookupResult &R, const DeclContext *DC) {
   //   name lookup. Instead, any conversion function templates visible in the
   //   context of the use are considered. [...]
   const CXXRecordDecl *Record = cast<CXXRecordDecl>(DC);
-  if (!Record->isCompleteDefinition())
+  if (!Record->isCompleteDefinition() && !R.isForRedeclaration())
     return Found;
 
   // For conversion operators, 'operator auto' should only match

diff  --git a/clang/test/SemaCXX/conversion-function.cpp b/clang/test/SemaCXX/conversion-function.cpp
index 717c73c4786eb..e00553fbb20a3 100644
--- a/clang/test/SemaCXX/conversion-function.cpp
+++ b/clang/test/SemaCXX/conversion-function.cpp
@@ -473,6 +473,24 @@ struct S {
 };
 }
 
+#if __cplusplus >= 201103L
+namespace GH218261 {
+  struct S {
+    template <typename T>
+    constexpr operator T() const {
+      return 10;
+    }
+
+    template <>
+    constexpr operator int() const {
+      return 4;
+    }
+  };
+
+  static_assert(S().operator int() == 4, "");
+}
+#endif
+
 #if __cplusplus >= 201103L
 namespace dependent_conversion_function_id_lookup {
 namespace gh77583 {