Stop evaluating trailing requires clause after overload resolution

Reported as it showed up as a constriants failure after the deferred
instantiation patch, we were checking constraints TWICE after overload
resolution.  The first is during overload resolution, the second is when
diagnosing a use.

This patch modifies DiagnoseUseOfDecl to skip the trailing requires
clause check in some cases. First, of course, after choosing a candidate
after overload resolution.

The second is when evaluating a shadow using constructor, which had its
constraints checked when picking a constructor (as this is ALWAYS an
overload situation!).

Differential Revision: https://reviews.llvm.org/D135772

clang/include/clang/Sema/Sema.h

@@ -5304,11 +5304,22 @@ public:
   // Expression Parsing Callbacks: SemaExpr.cpp.
 
   bool CanUseDecl(NamedDecl *D, bool TreatUnavailableAsInvalid);
+  // A version of DiagnoseUseOfDecl that should be used if overload resolution
+  // has been used to find this declaration, which means we don't have to bother
+  // checking the trailing requires clause.
+  bool DiagnoseUseOfOverloadedDecl(NamedDecl *D, SourceLocation Loc) {
+    return DiagnoseUseOfDecl(
+        D, Loc, /*UnknownObjCClass=*/nullptr, /*ObjCPropertyAccess=*/false,
+        /*AvoidPartialAvailabilityChecks=*/false, /*ClassReceiver=*/nullptr,
+        /*SkipTrailingRequiresClause=*/true);
+  }
+
   bool DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                          const ObjCInterfaceDecl *UnknownObjCClass = nullptr,
                          bool ObjCPropertyAccess = false,
                          bool AvoidPartialAvailabilityChecks = false,
-                         ObjCInterfaceDecl *ClassReciever = nullptr);
+                         ObjCInterfaceDecl *ClassReciever = nullptr,
+                         bool SkipTrailingRequiresClause = false);
   void NoteDeletedFunction(FunctionDecl *FD);
   void NoteDeletedInheritingConstructor(CXXConstructorDecl *CD);
   bool DiagnosePropertyAccessorMismatch(ObjCPropertyDecl *PD,

clang/lib/Sema/SemaDeclCXX.cpp

@@ -15551,7 +15551,10 @@ Sema::BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
                             SourceRange ParenRange) {
   if (auto *Shadow = dyn_cast<ConstructorUsingShadowDecl>(FoundDecl)) {
     Constructor = findInheritingConstructor(ConstructLoc, Constructor, Shadow);
-    if (DiagnoseUseOfDecl(Constructor, ConstructLoc))
+    // The only way to get here is if we did overlaod resolution to find the
+    // shadow decl, so we don't need to worry about re-checking the trailing
+    // requires clause.
+    if (DiagnoseUseOfOverloadedDecl(Constructor, ConstructLoc))
       return ExprError();
   }
 

clang/lib/Sema/SemaExpr.cpp

@@ -222,7 +222,8 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                              const ObjCInterfaceDecl *UnknownObjCClass,
                              bool ObjCPropertyAccess,
                              bool AvoidPartialAvailabilityChecks,
-                             ObjCInterfaceDecl *ClassReceiver) {
+                             ObjCInterfaceDecl *ClassReceiver,
+                             bool SkipTrailingRequiresClause) {
   SourceLocation Loc = Locs.front();
   if (getLangOpts().CPlusPlus && isa<FunctionDecl>(D)) {
     // If there were any diagnostics suppressed by template argument deduction,
@@ -281,7 +282,7 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
     // See if this is a function with constraints that need to be satisfied.
     // Check this before deducing the return type, as it might instantiate the
     // definition.
-    if (FD->getTrailingRequiresClause()) {
+    if (!SkipTrailingRequiresClause && FD->getTrailingRequiresClause()) {
       ConstraintSatisfaction Satisfaction;
       if (CheckFunctionConstraints(FD, Satisfaction, Loc,
                                    /*ForOverloadResolution*/ true))
@@ -6761,8 +6762,8 @@ ExprResult Sema::BuildCallExpr(Scope *Scope, Expr *Fn, SourceLocation LParenLoc,
             nullptr, DRE->isNonOdrUse());
       }
     }
-  } else if (isa<MemberExpr>(NakedFn))
+  } else if (auto *ME = dyn_cast<MemberExpr>(NakedFn))
-    NDecl = cast<MemberExpr>(NakedFn)->getMemberDecl();
+    NDecl = ME->getMemberDecl();
 
   if (FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(NDecl)) {
     if (CallingNDeclIndirectly && !checkAddressOfFunctionIsAvailable(

clang/lib/Sema/SemaOverload.cpp

@@ -14680,7 +14680,7 @@ ExprResult Sema::BuildCallToMemberFunction(Scope *S, Expr *MemExprE,
       Method = cast<CXXMethodDecl>(Best->Function);
       FoundDecl = Best->FoundDecl;
       CheckUnresolvedMemberAccess(UnresExpr, Best->FoundDecl);
-      if (DiagnoseUseOfDecl(Best->FoundDecl, UnresExpr->getNameLoc()))
+      if (DiagnoseUseOfOverloadedDecl(Best->FoundDecl, UnresExpr->getNameLoc()))
         break;
       // If FoundDecl is different from Method (such as if one is a template
       // and the other a specialization), make sure DiagnoseUseOfDecl is
@@ -14689,7 +14689,7 @@ ExprResult Sema::BuildCallToMemberFunction(Scope *S, Expr *MemExprE,
       // DiagnoseUseOfDecl to accept both the FoundDecl and the decl
       // being used.
       if (Method != FoundDecl.getDecl() &&
-                      DiagnoseUseOfDecl(Method, UnresExpr->getNameLoc()))
+          DiagnoseUseOfOverloadedDecl(Method, UnresExpr->getNameLoc()))
         break;
       Succeeded = true;
       break;

clang/test/SemaTemplate/concepts.cpp

@@ -708,3 +708,60 @@ Container<5>::var_templ<int> inst_fail;
 // expected-note@#CMVT_REQ{{because 'sizeof(int) == arity' (4 == 5) evaluated to false}}
 } // namespace ConstrainedMemberVarTemplate 
 
+// These should not diagnose, where we were unintentionally doing so before by
+// checking trailing requires clause twice, yet not having the ability to the
+// 2nd time, since it was no longer a dependent variant.
+namespace InheritedFromPartialSpec {
+template<class C>
+constexpr bool Check = true;
+
+template<typename T>
+struct Foo {
+  template<typename U>
+    Foo(U&&) requires (Check<U>){}
+  template<typename U>
+    void MemFunc(U&&) requires (Check<U>){}
+  template<typename U>
+    static void StaticMemFunc(U&&) requires (Check<U>){}
+  ~Foo() requires (Check<T>){}
+};
+
+template<>
+  struct Foo<void> : Foo<int> {
+    using Foo<int>::Foo;
+    using Foo<int>::MemFunc;
+    using Foo<int>::StaticMemFunc;
+  };
+
+void use() {
+  Foo<void> F {1.1};
+  F.MemFunc(1.1);
+  Foo<void>::StaticMemFunc(1.1);
+}
+
+template<typename T>
+struct counted_iterator {
+  constexpr auto operator->() const noexcept requires false {
+    return T::Invalid;
+  };
+};
+
+template<class _Ip>
+concept __has_member_pointer = requires { typename _Ip::pointer; };
+
+template<class>
+struct __iterator_traits_member_pointer_or_arrow_or_void { using type = void; };
+template<__has_member_pointer _Ip>
+struct __iterator_traits_member_pointer_or_arrow_or_void<_Ip> { using type = typename _Ip::pointer; };
+
+template<class _Ip>
+  requires requires(_Ip& __i) { __i.operator->(); } && (!__has_member_pointer<_Ip>)
+struct __iterator_traits_member_pointer_or_arrow_or_void<_Ip> {
+  using type = decltype(declval<_Ip&>().operator->());
+};
+
+
+void use2() {
+  __iterator_traits_member_pointer_or_arrow_or_void<counted_iterator<int>> f;
+}
+}// namespace InheritedFromPartialSpec