llvmbot wrote:

<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

<details>
<summary>Changes</summary>

For a dependent variable template specialization, we don't build a dependent 
Decl node or a DeclRefExpr to represent it. Instead, we preserve the 
UnresolvedLookupExpr until instantiation.

However, this approach isn't ideal for constraint normalization. We consider 
the qualifier during profiling, but since that's based on the written code, it 
can introduce confusing differences, even when the expressions resolve to the 
same declaration.

This change profiles the underlying VarTemplateDecl if UnresolvedLookupExpr is 
used to model a dependent use of it.

Fixes https://github.com/llvm/llvm-project/issues/139476

---
Full diff: https://github.com/llvm/llvm-project/pull/140680.diff


4 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+1) 
- (modified) clang/lib/AST/StmtProfile.cpp (+8-2) 
- (modified) clang/test/SemaCXX/exception-spec.cpp (+21) 
- (modified) clang/test/SemaTemplate/concepts-out-of-line-def.cpp (+15) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f04cb7b91788c..4c839303f3621 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -741,6 +741,7 @@ Bug Fixes to C++ Support
 - Fixed the handling of pack indexing types in the constraints of a member 
function redeclaration. (#GH138255)
 - Clang now correctly parses arbitrary order of ``[[]]``, ``__attribute__`` 
and ``alignas`` attributes for declarations (#GH133107)
 - Fixed a crash when forming an invalid function type in a dependent context. 
(#GH138657) (#GH115725) (#GH68852)
+- Fixed a function declaration mismatch that caused inconsistencies between 
concepts and variable template declarations. (#GH139476)
 - Clang no longer segfaults when there is a configuration mismatch between 
modules and their users (http://crbug.com/400353616).
 - Fix an incorrect deduction when calling an explicit object member function 
template through an overload set address.
 - Fixed bug in constant evaluation that would allow using the value of a
diff --git a/clang/lib/AST/StmtProfile.cpp b/clang/lib/AST/StmtProfile.cpp
index f7d1655f67ed1..2f1dec434c30b 100644
--- a/clang/lib/AST/StmtProfile.cpp
+++ b/clang/lib/AST/StmtProfile.cpp
@@ -2189,8 +2189,14 @@ StmtProfiler::VisitCXXPseudoDestructorExpr(const 
CXXPseudoDestructorExpr *S) {
 
 void StmtProfiler::VisitOverloadExpr(const OverloadExpr *S) {
   VisitExpr(S);
-  VisitNestedNameSpecifier(S->getQualifier());
-  VisitName(S->getName(), /*TreatAsDecl*/ true);
+  bool DescribingDependentVarTemplate =
+      S->getNumDecls() == 1 && isa<VarTemplateDecl>(*S->decls_begin());
+  if (DescribingDependentVarTemplate) {
+    VisitDecl(*S->decls_begin());
+  } else {
+    VisitNestedNameSpecifier(S->getQualifier());
+    VisitName(S->getName(), /*TreatAsDecl*/ true);
+  }
   ID.AddBoolean(S->hasExplicitTemplateArgs());
   if (S->hasExplicitTemplateArgs())
     VisitTemplateArguments(S->getTemplateArgs(), S->getNumTemplateArgs());
diff --git a/clang/test/SemaCXX/exception-spec.cpp 
b/clang/test/SemaCXX/exception-spec.cpp
index 6ad19aab397bd..31c691b28da4b 100644
--- a/clang/test/SemaCXX/exception-spec.cpp
+++ b/clang/test/SemaCXX/exception-spec.cpp
@@ -52,3 +52,24 @@ namespace AssignmentOp {
     D2 &operator=(const D2&); // expected-error {{more lax}}
   };
 }
+
+namespace OverloadedFunctions {
+
+template <typename T>
+void f(T&) noexcept;
+
+template <typename T, int N>
+void f(T (&arr)[N]) noexcept(noexcept(f(*arr)));
+
+template <typename T>
+inline void f(T&) noexcept {}
+
+template <typename T, int N>
+inline void f(T (&arr)[N]) noexcept(noexcept(f(*arr))) {}
+
+void g() {
+    int x[1];
+    f(x);
+}
+
+}
diff --git a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp 
b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
index e5d00491d3fb8..bf505dec0ca14 100644
--- a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
+++ b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
@@ -853,3 +853,18 @@ template <int... Ts>
 requires C<Ts...[0]>
 auto TplClass<int>::buggy() -> void {}
 }
+
+namespace GH139476 {
+
+namespace moo {
+  template <typename T>
+  constexpr bool baa = true;
+
+  template <typename T> requires baa<T>
+  void caw();
+}
+
+template <typename T> requires moo::baa<T>
+void moo::caw() {}
+
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/140680
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