[clang] [Clang] Consider outer instantiation scopes for constraint normalization (PR #114749)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

<details>
<summary>Changes</summary>

We need to compare constraint expressions when instantiating a friend declaration that is lexically defined within a class template. Since the evaluation is deferred, the expression might refer to untransformed function parameters such that the substitution needs the mapping of instantiation.

These mappings are maintained by the function declaration instantiation, so we need to establish a "transparent" LocalInstantiationScope before substituting into the constraint.

No release note as this fixes a regression in 19.

Fixes https://github.com/llvm/llvm-project/issues/114685

---
Full diff: https://github.com/llvm/llvm-project/pull/114749.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaConcept.cpp (+1-1) 
- (modified) clang/test/SemaTemplate/concepts-out-of-line-def.cpp (+16) 


``````````diff
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index e36ee062213716..bc988001ea7e46 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -975,7 +975,7 @@ static const Expr *SubstituteConstraintExpressionWithoutSatisfaction(
   std::optional<LocalInstantiationScope> ScopeForParameters;
   if (const NamedDecl *ND = DeclInfo.getDecl();
       ND && ND->isFunctionOrFunctionTemplate()) {
-    ScopeForParameters.emplace(S);
+    ScopeForParameters.emplace(S, /*CombineWithOuterScope=*/true);
     const FunctionDecl *FD = ND->getAsFunction();
     for (auto *PVD : FD->parameters()) {
       if (!PVD->isParameterPack()) {
diff --git a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
index fe8f74928fc370..dd518d283c83c8 100644
--- a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
+++ b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
@@ -702,3 +702,19 @@ class TTP;
 C v;
 
 } // namespace GH93099
+
+namespace GH114685 {
+
+template <typename T> struct ptr {
+  template <typename U>
+  friend ptr<U> make_item(auto &&args)
+    requires(sizeof(args) > 1);
+};
+
+template <typename U>
+ptr<U> make_item(auto &&args)
+  requires(sizeof(args) > 1) {}
+
+ptr<char> p;
+
+} // namespace GH114685

``````````

</details>


https://github.com/llvm/llvm-project/pull/114749