[Clang][Sema] Substitute constraints only for declarations with different lexical contexts

Substitute constraints only for declarations with different lexical contexts.
This results in avoiding the substitution of constraints during the redeclaration check
inside a class (and by product caching the wrong substitution result).

Test plan: ninja check-all

Differential revision: https://reviews.llvm.org/D150730

2 files changed, 36 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 1126c2c517fe..2f5fb8f8d029 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -780,7 +780,9 @@ bool Sema::AreConstraintExpressionsEqual(const NamedDecl *Old,
                                          const Expr *NewConstr) {
   if (OldConstr == NewConstr)
     return true;
-  if (Old && New && Old != New) {
+  // C++ [temp.constr.decl]p4
+  if (Old && New && Old != New &&
+      Old->getLexicalDeclContext() != New->getLexicalDeclContext()) {
     if (const Expr *SubstConstr =
             SubstituteConstraintExpression(*this, Old, OldConstr))
       OldConstr = SubstConstr;
diff --git a/clang/test/SemaTemplate/concepts-no-early-substitution.cpp b/clang/test/SemaTemplate/concepts-no-early-substitution.cpp
new file mode 100644
index 000000000000..9e576f16a263
--- /dev/null
+++ b/clang/test/SemaTemplate/concepts-no-early-substitution.cpp
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -std=c++20 -x c++ %s -verify -fsyntax-only
+// expected-no-diagnostics
+
+template <typename T0>
+concept HasMemberBegin = requires(T0 t) { t.begin(); };
+
+struct GetBegin {
+  template <HasMemberBegin T1>
+  void operator()(T1);
+};
+
+GetBegin begin;
+
+template <typename T2>
+concept Concept = requires(T2 t) { begin(t); };
+
+struct Subrange;
+
+template <typename T3>
+struct View {
+  Subrange &getSubrange();
+
+  operator bool()
+    requires true;
+
+  operator bool()
+    requires requires { begin(getSubrange()); };
+
+  void begin();
+};
+
+struct Subrange : View<void> {};
+static_assert(Concept<Subrange>);