[PATCH] D122083: [Concepts] Fix placeholder constraints when references are involved

[Roy Jacobson via Phabricator via cfe-commits]

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Placeholder types were not checked for constraint satisfaction when modified by references.
GitHub issue #54443


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122083

Files:
  clang/lib/Sema/SemaTemplateDeduction.cpp
  clang/test/SemaTemplate/concepts.cpp


Index: clang/test/SemaTemplate/concepts.cpp
===================================================================
--- clang/test/SemaTemplate/concepts.cpp
+++ clang/test/SemaTemplate/concepts.cpp
@@ -171,7 +171,7 @@
 }
 
 namespace PR49188 {
-  template<class T> concept C = false;     // expected-note 6 {{because 'false' evaluated to false}}
+  template<class T> concept C = false;     // expected-note 7 {{because 'false' evaluated to false}}
 
   C auto f1() { // expected-error {{deduced type 'void' does not satisfy 'C'}}
     return void();
@@ -189,7 +189,7 @@
   }
   C decltype(auto) f6() { // expected-error {{deduced type 'void' does not satisfy 'C'}}
   }
-  C auto& f7() { // expected-error {{cannot form a reference to 'void'}}
+  C auto& f7() { // expected-error {{deduced type 'void' does not satisfy 'C'}}
     return void();
   }
   C auto& f8() {
@@ -222,3 +222,26 @@
 };
 void (*f2)() = B::f; // expected-error {{address of overloaded function 'f' does not match required type}}
 }
+
+namespace PR54443 {
+
+template <class T, class U>
+struct is_same { static constexpr bool value = false; };
+
+template <class T>
+struct is_same<T, T> { static constexpr bool value = true; };
+
+template <class T, class U>
+concept same_as = is_same<T, U>::value; // expected-note-re 4 {{because {{.*}} evaluated to false}}
+
+int const &f();
+
+same_as<int const> auto i1 = f(); // expected-error {{deduced type 'int' does not satisfy 'same_as<const int>'}}
+same_as<int const> auto &i2 = f();
+same_as<int const> auto &&i3 = f(); // expected-error {{deduced type 'const int &' does not satisfy 'same_as<const int>'}}
+
+same_as<int const &> auto i4 = f(); // expected-error {{deduced type 'int' does not satisfy 'same_as<const int &>'}}
+same_as<int const &> auto &i5 = f(); // expected-error {{deduced type 'const int' does not satisfy 'same_as<const int &>'}}
+same_as<int const &> auto &&i6 = f();
+
+}
Index: clang/lib/Sema/SemaTemplateDeduction.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateDeduction.cpp
+++ clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -4769,7 +4769,8 @@
       return DAR_FailedAlreadyDiagnosed;
   }
 
-  if (const auto *AT = Type.getType()->getAs<AutoType>()) {
+  if (const auto *AT =
+          Type.getType().getNonReferenceType()->getAs<AutoType>()) {
     if (AT->isConstrained() && !IgnoreConstraints) {
       auto ConstraintsResult =
           CheckDeducedPlaceholderConstraints(*this, *AT,


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