[Clang][Sema] Make UnresolvedLookupExprs in class scope explicit specializations instantiation dependent (#100392)

A class member named by an expression in a member function that may instantiate to a static _or_ non-static member is represented by a `UnresolvedLookupExpr` in order to defer the implicit transformation to a class member access expression until instantiation. Since `ASTContext::getDecltypeType` only creates a `DecltypeType` that has a `DependentDecltypeType` as its canonical type when the operand is instantiation dependent, and since we do not transform types unless they are instantiation dependent, we need to mark the `UnresolvedLookupExpr` as instantiation dependent in order to correctly build a `DecltypeType` using the expression as its operand with a `DependentDecltypeType` canonical type. Fixes #99873. 

13 files changed, 64 insertions, 28 deletions

diff --git a/clang/include/clang/AST/ExprCXX.h b/clang/include/clang/AST/ExprCXX.h
index f86f181..847a6ea 100644
--- a/clang/include/clang/AST/ExprCXX.h
+++ b/clang/include/clang/AST/ExprCXX.h
@@ -3229,7 +3229,7 @@ class UnresolvedLookupExpr final
                        const DeclarationNameInfo &NameInfo, bool RequiresADL,
                        const TemplateArgumentListInfo *TemplateArgs,
                        UnresolvedSetIterator Begin, UnresolvedSetIterator End,
-                       bool KnownDependent);
+                       bool KnownDependent, bool KnownInstantiationDependent);
 
   UnresolvedLookupExpr(EmptyShell Empty, unsigned NumResults,
                        bool HasTemplateKWAndArgsInfo);
@@ -3248,7 +3248,7 @@ public:
          NestedNameSpecifierLoc QualifierLoc,
          const DeclarationNameInfo &NameInfo, bool RequiresADL,
          UnresolvedSetIterator Begin, UnresolvedSetIterator End,
-         bool KnownDependent);
+         bool KnownDependent, bool KnownInstantiationDependent);
 
   // After canonicalization, there may be dependent template arguments in
   // CanonicalConverted But none of Args is dependent. When any of
@@ -3258,7 +3258,8 @@ public:
          NestedNameSpecifierLoc QualifierLoc, SourceLocation TemplateKWLoc,
          const DeclarationNameInfo &NameInfo, bool RequiresADL,
          const TemplateArgumentListInfo *Args, UnresolvedSetIterator Begin,
-         UnresolvedSetIterator End, bool KnownDependent);
+         UnresolvedSetIterator End, bool KnownDependent,
+         bool KnownInstantiationDependent);
 
   static UnresolvedLookupExpr *CreateEmpty(const ASTContext &Context,
                                            unsigned NumResults,
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index c835b72..26b724d 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -8633,13 +8633,15 @@ ASTNodeImporter::VisitUnresolvedLookupExpr(UnresolvedLookupExpr *E) {
     return UnresolvedLookupExpr::Create(
         Importer.getToContext(), *ToNamingClassOrErr, *ToQualifierLocOrErr,
         *ToTemplateKeywordLocOrErr, ToNameInfo, E->requiresADL(), &ToTAInfo,
-        ToDecls.begin(), ToDecls.end(), KnownDependent);
+        ToDecls.begin(), ToDecls.end(), KnownDependent,
+        /*KnownInstantiationDependent=*/E->isInstantiationDependent());
   }
 
   return UnresolvedLookupExpr::Create(
       Importer.getToContext(), *ToNamingClassOrErr, *ToQualifierLocOrErr,
       ToNameInfo, E->requiresADL(), ToDecls.begin(), ToDecls.end(),
-      /*KnownDependent=*/E->isTypeDependent());
+      /*KnownDependent=*/E->isTypeDependent(),
+      /*KnownInstantiationDependent=*/E->isInstantiationDependent());
 }
 
 ExpectedStmt
diff --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
index 6212989..83ce404 100644
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -402,10 +402,11 @@ UnresolvedLookupExpr::UnresolvedLookupExpr(
     NestedNameSpecifierLoc QualifierLoc, SourceLocation TemplateKWLoc,
     const DeclarationNameInfo &NameInfo, bool RequiresADL,
     const TemplateArgumentListInfo *TemplateArgs, UnresolvedSetIterator Begin,
-    UnresolvedSetIterator End, bool KnownDependent)
+    UnresolvedSetIterator End, bool KnownDependent,
+    bool KnownInstantiationDependent)
     : OverloadExpr(UnresolvedLookupExprClass, Context, QualifierLoc,
                    TemplateKWLoc, NameInfo, TemplateArgs, Begin, End,
-                   KnownDependent, false, false),
+                   KnownDependent, KnownInstantiationDependent, false),
       NamingClass(NamingClass) {
   UnresolvedLookupExprBits.RequiresADL = RequiresADL;
 }
@@ -420,7 +421,7 @@ UnresolvedLookupExpr *UnresolvedLookupExpr::Create(
     const ASTContext &Context, CXXRecordDecl *NamingClass,
     NestedNameSpecifierLoc QualifierLoc, const DeclarationNameInfo &NameInfo,
     bool RequiresADL, UnresolvedSetIterator Begin, UnresolvedSetIterator End,
-    bool KnownDependent) {
+    bool KnownDependent, bool KnownInstantiationDependent) {
   unsigned NumResults = End - Begin;
   unsigned Size = totalSizeToAlloc<DeclAccessPair, ASTTemplateKWAndArgsInfo,
                                    TemplateArgumentLoc>(NumResults, 0, 0);
@@ -428,7 +429,8 @@ UnresolvedLookupExpr *UnresolvedLookupExpr::Create(
   return new (Mem) UnresolvedLookupExpr(
       Context, NamingClass, QualifierLoc,
       /*TemplateKWLoc=*/SourceLocation(), NameInfo, RequiresADL,
-      /*TemplateArgs=*/nullptr, Begin, End, KnownDependent);
+      /*TemplateArgs=*/nullptr, Begin, End, KnownDependent,
+      KnownInstantiationDependent);
 }
 
 UnresolvedLookupExpr *UnresolvedLookupExpr::Create(
@@ -436,7 +438,8 @@ UnresolvedLookupExpr *UnresolvedLookupExpr::Create(
     NestedNameSpecifierLoc QualifierLoc, SourceLocation TemplateKWLoc,
     const DeclarationNameInfo &NameInfo, bool RequiresADL,
     const TemplateArgumentListInfo *Args, UnresolvedSetIterator Begin,
-    UnresolvedSetIterator End, bool KnownDependent) {
+    UnresolvedSetIterator End, bool KnownDependent,
+    bool KnownInstantiationDependent) {
   unsigned NumResults = End - Begin;
   bool HasTemplateKWAndArgsInfo = Args || TemplateKWLoc.isValid();
   unsigned NumTemplateArgs = Args ? Args->size() : 0;
@@ -444,9 +447,9 @@ UnresolvedLookupExpr *UnresolvedLookupExpr::Create(
                                    TemplateArgumentLoc>(
       NumResults, HasTemplateKWAndArgsInfo, NumTemplateArgs);
   void *Mem = Context.Allocate(Size, alignof(UnresolvedLookupExpr));
-  return new (Mem) UnresolvedLookupExpr(Context, NamingClass, QualifierLoc,
-                                        TemplateKWLoc, NameInfo, RequiresADL,
-                                        Args, Begin, End, KnownDependent);
+  return new (Mem) UnresolvedLookupExpr(
+      Context, NamingClass, QualifierLoc, TemplateKWLoc, NameInfo, RequiresADL,
+      Args, Begin, End, KnownDependent, KnownInstantiationDependent);
 }
 
 UnresolvedLookupExpr *UnresolvedLookupExpr::CreateEmpty(
diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index 68ad6e3..1bb8955 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -838,7 +838,8 @@ ExprResult Sema::BuildOperatorCoawaitLookupExpr(Scope *S, SourceLocation Loc) {
   Expr *CoawaitOp = UnresolvedLookupExpr::Create(
       Context, /*NamingClass*/ nullptr, NestedNameSpecifierLoc(),
       DeclarationNameInfo(OpName, Loc), /*RequiresADL*/ true, Functions.begin(),
-      Functions.end(), /*KnownDependent=*/false);
+      Functions.end(), /*KnownDependent=*/false,
+      /*KnownInstantiationDependent=*/false);
   assert(CoawaitOp);
   return CoawaitOp;
 }
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index bab32b9..1da16d6 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1219,7 +1219,7 @@ Corrected:
   return NameClassification::OverloadSet(UnresolvedLookupExpr::Create(
       Context, Result.getNamingClass(), SS.getWithLocInContext(Context),
       Result.getLookupNameInfo(), ADL, Result.begin(), Result.end(),
-      /*KnownDependent=*/false));
+      /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false));
 }
 
 ExprResult
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 5782daa..cb0a589 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -1289,7 +1289,7 @@ static bool checkTupleLikeDecomposition(Sema &S,
           S.Context, nullptr, NestedNameSpecifierLoc(), SourceLocation(),
           DeclarationNameInfo(GetDN, Loc), /*RequiresADL=*/true, &Args,
           UnresolvedSetIterator(), UnresolvedSetIterator(),
-          /*KnownDependent=*/false);
+          /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false);
 
       Expr *Arg = E.get();
       E = S.BuildCallExpr(nullptr, Get, Loc, Arg, Loc);
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 72cd92a..21c8ae6 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -3188,7 +3188,7 @@ ExprResult Sema::BuildDeclarationNameExpr(const CXXScopeSpec &SS,
   UnresolvedLookupExpr *ULE = UnresolvedLookupExpr::Create(
       Context, R.getNamingClass(), SS.getWithLocInContext(Context),
       R.getLookupNameInfo(), NeedsADL, R.begin(), R.end(),
-      /*KnownDependent=*/false);
+      /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false);
 
   return ULE;
 }
diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index 2070f3b..f1ba26f 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -331,7 +331,8 @@ ExprResult Sema::BuildPossibleImplicitMemberExpr(
     return UnresolvedLookupExpr::Create(
         Context, R.getNamingClass(), SS.getWithLocInContext(Context),
         TemplateKWLoc, R.getLookupNameInfo(), /*RequiresADL=*/false,
-        TemplateArgs, R.begin(), R.end(), /*KnownDependent=*/true);
+        TemplateArgs, R.begin(), R.end(), /*KnownDependent=*/true,
+        /*KnownInstantiationDependent=*/true);
 
   case IMA_Error_StaticOrExplicitContext:
   case IMA_Error_Unrelated:
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index 7d814e6b..b5978dd 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -17932,7 +17932,8 @@ buildDeclareReductionRef(Sema &SemaRef, SourceLocation Loc, SourceRange Range,
     return UnresolvedLookupExpr::Create(
         SemaRef.Context, /*NamingClass=*/nullptr,
         ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context), ReductionId,
-        /*ADL=*/true, ResSet.begin(), ResSet.end(), /*KnownDependent=*/false);
+        /*ADL=*/true, ResSet.begin(), ResSet.end(), /*KnownDependent=*/false,
+        /*KnownInstantiationDependent=*/false);
   }
   // Lookup inside the classes.
   // C++ [over.match.oper]p3:
@@ -20798,7 +20799,8 @@ static ExprResult buildUserDefinedMapperRef(Sema &SemaRef, Scope *S,
     return UnresolvedLookupExpr::Create(
         SemaRef.Context, /*NamingClass=*/nullptr,
         MapperIdScopeSpec.getWithLocInContext(SemaRef.Context), MapperId,
-        /*ADL=*/false, URS.begin(), URS.end(), /*KnownDependent=*/false);
+        /*ADL=*/false, URS.begin(), URS.end(), /*KnownDependent=*/false,
+        /*KnownInstantiationDependent=*/false);
   }
   SourceLocation Loc = MapperId.getLoc();
   // [OpenMP 5.0], 2.19.7.3 declare mapper Directive, Restrictions
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 54a9bba..fd88b6a 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -14093,9 +14093,9 @@ ExprResult Sema::CreateUnresolvedLookupExpr(CXXRecordDecl *NamingClass,
                                             DeclarationNameInfo DNI,
                                             const UnresolvedSetImpl &Fns,
                                             bool PerformADL) {
-  return UnresolvedLookupExpr::Create(Context, NamingClass, NNSLoc, DNI,
-                                      PerformADL, Fns.begin(), Fns.end(),
-                                      /*KnownDependent=*/false);
+  return UnresolvedLookupExpr::Create(
+      Context, NamingClass, NNSLoc, DNI, PerformADL, Fns.begin(), Fns.end(),
+      /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false);
 }
 
 ExprResult Sema::BuildCXXMemberCallExpr(Expr *E, NamedDecl *FoundDecl,
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 6e2cb59..cd3ee31 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -4436,7 +4436,8 @@ ExprResult Sema::BuildTemplateIdExpr(const CXXScopeSpec &SS,
   UnresolvedLookupExpr *ULE = UnresolvedLookupExpr::Create(
       Context, R.getNamingClass(), SS.getWithLocInContext(Context),
       TemplateKWLoc, R.getLookupNameInfo(), RequiresADL, TemplateArgs,
-      R.begin(), R.end(), KnownDependent);
+      R.begin(), R.end(), KnownDependent,
+      /*KnownInstantiationDependent=*/false);
 
   // Model the templates with UnresolvedTemplateTy. The expression should then
   // either be transformed in an instantiation or be diagnosed in
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 26b3c83..84dcf66 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -10687,7 +10687,7 @@ TreeTransform<Derived>::TransformOMPReductionClause(OMPReductionClause *C) {
           SemaRef.Context, /*NamingClass=*/nullptr,
           ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context), NameInfo,
           /*ADL=*/true, Decls.begin(), Decls.end(),
-          /*KnownDependent=*/false));
+          /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false));
     } else
       UnresolvedReductions.push_back(nullptr);
   }
@@ -10734,7 +10734,7 @@ OMPClause *TreeTransform<Derived>::TransformOMPTaskReductionClause(
           SemaRef.Context, /*NamingClass=*/nullptr,
           ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context), NameInfo,
           /*ADL=*/true, Decls.begin(), Decls.end(),
-          /*KnownDependent=*/false));
+          /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false));
     } else
       UnresolvedReductions.push_back(nullptr);
   }
@@ -10780,7 +10780,7 @@ TreeTransform<Derived>::TransformOMPInReductionClause(OMPInReductionClause *C) {
           SemaRef.Context, /*NamingClass=*/nullptr,
           ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context), NameInfo,
           /*ADL=*/true, Decls.begin(), Decls.end(),
-          /*KnownDependent=*/false));
+          /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false));
     } else
       UnresolvedReductions.push_back(nullptr);
   }
@@ -10962,7 +10962,7 @@ bool transformOMPMappableExprListClause(
           TT.getSema().Context, /*NamingClass=*/nullptr,
           MapperIdScopeSpec.getWithLocInContext(TT.getSema().Context),
           MapperIdInfo, /*ADL=*/true, Decls.begin(), Decls.end(),
-          /*KnownDependent=*/false));
+          /*KnownDependent=*/false, /*KnownInstantiationDependent=*/false));
     } else {
       UnresolvedMappers.push_back(nullptr);
     }
diff --git a/clang/test/SemaCXX/decltype.cpp b/clang/test/SemaCXX/decltype.cpp
index 9961c5e..76d6a041 100644
--- a/clang/test/SemaCXX/decltype.cpp
+++ b/clang/test/SemaCXX/decltype.cpp
@@ -147,6 +147,31 @@ namespace GH97646 {
   }
 }
 
+namespace GH99873 {
+struct B {
+  int x;
+};
+
+template<typename T>
+struct A {
+  template<typename U>
+  constexpr int f() const {
+    return 1;
+  }
+
+  template<>
+  constexpr int f<int>() const {
+    return decltype(B::x)();
+  }
+};
+
+// This shouldn't crash.
+static_assert(A<int>().f<int>() == 0, "");
+// The result should not be dependent.
+static_assert(A<int>().f<int>() != 0, ""); // expected-error {{static assertion failed due to requirement 'GH99873::A<int>().f<int>() != 0'}}
+                                           // expected-note@-1 {{expression evaluates to '0 != 0'}}
+}
+
 template<typename>
 class conditional {
 };