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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

<details>
<summary>Changes</summary>

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

---
Full diff: https://github.com/llvm/llvm-project/pull/158414.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaTemplateDeduction.cpp (+1-1) 
- (modified) clang/test/SemaTemplate/concepts.cpp (+21) 


``````````diff
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}}

``````````

</details>


https://github.com/llvm/llvm-project/pull/158414