[clang] 9ac2924 - [Clang] Fix the source location of default template arguments in placeholder constraints (#158414)

[via cfe-commits]

Author: Younan Zhang
Date: 2025-09-13T18:03:13+08:00
New Revision: 9ac292441fcc4ebbaf4c7c36a9b2e2dd32580be0

URL: https://github.com/llvm/llvm-project/commit/9ac292441fcc4ebbaf4c7c36a9b2e2dd32580be0
DIFF: https://github.com/llvm/llvm-project/commit/9ac292441fcc4ebbaf4c7c36a9b2e2dd32580be0.diff

LOG: [Clang] Fix the source location of default template arguments in placeholder constraints (#158414)

We discovered this issue while working on the concept normalization
refactoring. We missed the source location when diagnosing the
instantiation point of the placeholder constraints, which is involved by
the substitution of default template arguments that happens before
constraint evaluation.

See the issue alive: https://godbolt.org/z/cWr9qP3E8

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaTemplateDeduction.cpp
    clang/test/SemaTemplate/concepts.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 51e5973098c14..6eb2a52e80ba9 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -285,6 +285,9 @@ Improvements to Clang's diagnostics
 
 - Clang now looks through parenthesis for ``-Wundefined-reinterpret-cast`` diagnostic.
 
+- Fixed a bug where the source location was missing when diagnosing ill-formed
+  placeholder constraints.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

diff  --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 64be2aab259f5..62e867c44ad14 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -5180,7 +5180,7 @@ static bool CheckDeducedPlaceholderConstraints(Sema &S, const AutoType &Type,
     TemplateArgs.addArgument(TypeLoc.getArgLoc(I));
 
   Sema::CheckTemplateArgumentInfo CTAI;
-  if (S.CheckTemplateArgumentList(Concept, SourceLocation(), TemplateArgs,
+  if (S.CheckTemplateArgumentList(Concept, TypeLoc.getNameLoc(), TemplateArgs,
                                   /*DefaultArgs=*/{},
                                   /*PartialTemplateArgs=*/false, CTAI))
     return true;

diff  --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index d63ad01b35800..209e7dc69797d 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -1251,6 +1251,27 @@ int i = SVGPropertyOwnerRegistry<SVGCircleElement>::fastAnimatedPropertyLookup()
 
 }
 
+namespace GH61824 {
+
+template<typename T, typename U = typename T::type> // #T_Type
+concept C = true;
+
+constexpr bool f(C auto) { // #GH61824_f
+  return true;
+}
+
+C auto x = 0;
+// expected-error@#T_Type {{type 'int' cannot be used prior to '::'}} \
+// expected-note at -1 {{in instantiation of default argument}}
+
+// This will be fixed when we merge https://github.com/llvm/llvm-project/pull/141776
+// Which makes us behave like GCC.
+static_assert(f(0));
+// expected-error at -1 {{no matching function for call}} \
+// expected-note@#GH61824_f {{constraints not satisfied}} \
+// expected-note@#T_Type {{type 'int' cannot be used prior to '::'}}
+
+}
 
 namespace GH149986 {
 template <typename T> concept PerfectSquare = [](){} // expected-note 2{{here}}