[Clang][Sema] Diagnose class member access expressions naming non-existent members of the current instantiation prior to instantiation in the absence of dependent base classes (llvm#84050)

Consider the following:
```cpp
template<typename T>
struct A
{
    auto f()
    {
        return this->x;
    }
};
```
Although `A` has no dependent base classes and the lookup context for
`x` is the current instantiation, we currently do not diagnose the
absence of a member `x` until `A<T>::f` is instantiated. This patch
moves the point of diagnosis for such expressions to occur at the point
of definition (i.e. prior to instantiation).

Author: sdkrystian

clang-tools-extra/clangd/unittests/FindTargetTests.cpp

@@ -854,7 +854,7 @@ TEST_F(TargetDeclTest, DependentExprs) {
           }
         };
       )cpp";
-  EXPECT_DECLS("CXXDependentScopeMemberExpr", "void foo()");
+  EXPECT_DECLS("MemberExpr", "void foo()");
 
   // Similar to above but base expression involves a function call.
   Code = R"cpp(
@@ -872,7 +872,7 @@ TEST_F(TargetDeclTest, DependentExprs) {
           }
         };
       )cpp";
-  EXPECT_DECLS("CXXDependentScopeMemberExpr", "void foo()");
+  EXPECT_DECLS("MemberExpr", "void foo()");
 
   // Similar to above but uses a function pointer.
   Code = R"cpp(
@@ -891,7 +891,7 @@ TEST_F(TargetDeclTest, DependentExprs) {
           }
         };
       )cpp";
-  EXPECT_DECLS("CXXDependentScopeMemberExpr", "void foo()");
+  EXPECT_DECLS("MemberExpr", "void foo()");
 
   // Base expression involves a member access into this.
   Code = R"cpp(
@@ -962,7 +962,7 @@ TEST_F(TargetDeclTest, DependentExprs) {
           void Foo() { this->[[find]](); }
         };
   )cpp";
-  EXPECT_DECLS("CXXDependentScopeMemberExpr", "void find()");
+  EXPECT_DECLS("MemberExpr", "void find()");
 }
 
 TEST_F(TargetDeclTest, DependentTypes) {

clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp

@@ -621,7 +621,7 @@ sizeof...($TemplateParameter[[Elements]]);
       struct $Class_def[[Foo]] {
         int $Field_decl[[Waldo]];
         void $Method_def[[bar]]() {
-          $Class[[Foo]]().$Field_dependentName[[Waldo]];
+          $Class[[Foo]]().$Field[[Waldo]];
         }
         template $Bracket[[<]]typename $TemplateParameter_def[[U]]$Bracket[[>]]
         void $Method_def[[bar1]]() {

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/owning-memory.cpp

@@ -309,6 +309,8 @@ struct HeapArray {                                          // Ok, since destruc
 
   HeapArray(HeapArray &&other) : _data(other._data), size(other.size) { // Ok
     other._data = nullptr;                                              // Ok
+    // CHECK-NOTES: [[@LINE-1]]:5: warning: expected assignment source to be of type 'gsl::owner<>'; got 'std::nullptr_t'
+    // FIXME: This warning is emitted because an ImplicitCastExpr for the NullToPointer conversion isn't created for dependent types.
     other.size = 0;
   }
 

clang-tools-extra/test/clang-tidy/checkers/modernize/use-equals-default-copy.cpp

@@ -260,6 +260,8 @@ template <class T>
 struct Template {
   Template() = default;
   Template(const Template &Other) : Field(Other.Field) {}
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use '= default'
+  // CHECK-FIXES: Template(const Template &Other)  = default;
   Template &operator=(const Template &Other);
   void foo(const T &t);
   int Field;
@@ -269,8 +271,12 @@ Template<T> &Template<T>::operator=(const Template<T> &Other) {
   Field = Other.Field;
   return *this;
 }
+// CHECK-MESSAGES: :[[@LINE-4]]:27: warning: use '= default'
+// CHECK-FIXES: Template<T> &Template<T>::operator=(const Template<T> &Other) = default;
+
 Template<int> T1;
 
+
 // Dependent types.
 template <class T>
 struct DT1 {
@@ -284,6 +290,9 @@ DT1<T> &DT1<T>::operator=(const DT1<T> &Other) {
   Field = Other.Field;
   return *this;
 }
+// CHECK-MESSAGES: :[[@LINE-4]]:17: warning: use '= default'
+// CHECK-FIXES: DT1<T> &DT1<T>::operator=(const DT1<T> &Other) = default;
+
 DT1<int> Dt1;
 
 template <class T>
@@ -303,6 +312,9 @@ DT2<T> &DT2<T>::operator=(const DT2<T> &Other) {
 struct T {
   typedef int TT;
 };
+// CHECK-MESSAGES: :[[@LINE-8]]:17: warning: use '= default'
+// CHECK-FIXES: DT2<T> &DT2<T>::operator=(const DT2<T> &Other) = default;
+
 DT2<T> Dt2;
 
 // Default arguments.

clang/docs/ReleaseNotes.rst

@@ -385,6 +385,18 @@ Improvements to Clang's diagnostics
 
 - Clang now diagnoses requires expressions with explicit object parameters.
 
+- Clang now looks up members of the current instantiation in the template definition context
+  if the current instantiation has no dependent base classes.
+
+  .. code-block:: c++
+
+     template<typename T>
+     struct A {
+       int f() {
+         return this->x; // error: no member named 'x' in 'A<T>'
+       }
+     };
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Sema/Lookup.h

@@ -499,7 +499,9 @@ class LookupResult {
   /// Note that while no result was found in the current instantiation,
   /// there were dependent base classes that could not be searched.
   void setNotFoundInCurrentInstantiation() {
-    assert(ResultKind == NotFound && Decls.empty());
+    assert((ResultKind == NotFound ||
+            ResultKind == NotFoundInCurrentInstantiation) &&
+           Decls.empty());
     ResultKind = NotFoundInCurrentInstantiation;
   }
 

clang/include/clang/Sema/Sema.h

@@ -7472,7 +7472,7 @@ class Sema final : public SemaBase {
   bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                            CXXScopeSpec &SS);
   bool LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
-                        bool AllowBuiltinCreation = false,
+                        QualType ObjectType, bool AllowBuiltinCreation = false,
                         bool EnteringContext = false);
   ObjCProtocolDecl *LookupProtocol(
       IdentifierInfo *II, SourceLocation IdLoc,
@@ -8881,11 +8881,13 @@ class Sema final : public SemaBase {
     /// functions (but no function templates).
     FoundFunctions,
   };
-  bool LookupTemplateName(
-      LookupResult &R, Scope *S, CXXScopeSpec &SS, QualType ObjectType,
-      bool EnteringContext, bool &MemberOfUnknownSpecialization,
-      RequiredTemplateKind RequiredTemplate = SourceLocation(),
-      AssumedTemplateKind *ATK = nullptr, bool AllowTypoCorrection = true);
+
+  bool
+  LookupTemplateName(LookupResult &R, Scope *S, CXXScopeSpec &SS,
+                     QualType ObjectType, bool EnteringContext,
+                     RequiredTemplateKind RequiredTemplate = SourceLocation(),
+                     AssumedTemplateKind *ATK = nullptr,
+                     bool AllowTypoCorrection = true);
 
   TemplateNameKind isTemplateName(Scope *S, CXXScopeSpec &SS,
                                   bool hasTemplateKeyword,

clang/lib/AST/Expr.cpp

@@ -103,7 +103,7 @@ const Expr *Expr::skipRValueSubobjectAdjustments(
       }
     } else if (const auto *ME = dyn_cast<MemberExpr>(E)) {
       if (!ME->isArrow()) {
-        assert(ME->getBase()->getType()->isRecordType());
+        assert(ME->getBase()->getType()->getAsRecordDecl());
         if (const auto *Field = dyn_cast<FieldDecl>(ME->getMemberDecl())) {
           if (!Field->isBitField() && !Field->getType()->isReferenceType()) {
             E = ME->getBase();

clang/lib/Parse/ParseDecl.cpp

@@ -2998,7 +2998,7 @@ bool Parser::ParseImplicitInt(DeclSpec &DS, CXXScopeSpec *SS,
         << TokenName << TagName << getLangOpts().CPlusPlus
         << FixItHint::CreateInsertion(Tok.getLocation(), FixitTagName);
 
-      if (Actions.LookupParsedName(R, getCurScope(), SS)) {
+      if (Actions.LookupName(R, getCurScope())) {
         for (LookupResult::iterator I = R.begin(), IEnd = R.end();
              I != IEnd; ++I)
           Diag((*I)->getLocation(), diag::note_decl_hiding_tag_type)

clang/lib/Sema/HLSLExternalSemaSource.cpp

@@ -126,12 +126,15 @@ struct BuiltinTypeDeclBuilder {
 
   static DeclRefExpr *lookupBuiltinFunction(ASTContext &AST, Sema &S,
                                             StringRef Name) {
-    CXXScopeSpec SS;
     IdentifierInfo &II = AST.Idents.get(Name, tok::TokenKind::identifier);
     DeclarationNameInfo NameInfo =
         DeclarationNameInfo(DeclarationName(&II), SourceLocation());
     LookupResult R(S, NameInfo, Sema::LookupOrdinaryName);
-    S.LookupParsedName(R, S.getCurScope(), &SS, false);
+    // AllowBuiltinCreation is false but LookupDirect will create
+    // the builtin when searching the global scope anyways...
+    S.LookupName(R, S.getCurScope());
+    // FIXME: If the builtin function was user-declared in global scope,
+    // this assert *will* fail. Should this call LookupBuiltin instead?
     assert(R.isSingleResult() &&
            "Since this is a builtin it should always resolve!");
     auto *VD = cast<ValueDecl>(R.getFoundDecl());

clang/lib/Sema/SemaAttr.cpp

@@ -837,7 +837,7 @@ void Sema::ActOnPragmaUnused(const Token &IdTok, Scope *curScope,
 
   IdentifierInfo *Name = IdTok.getIdentifierInfo();
   LookupResult Lookup(*this, Name, IdTok.getLocation(), LookupOrdinaryName);
-  LookupParsedName(Lookup, curScope, nullptr, true);
+  LookupName(Lookup, curScope, /*AllowBuiltinCreation=*/true);
 
   if (Lookup.empty()) {
     Diag(PragmaLoc, diag::warn_pragma_unused_undeclared_var)

clang/lib/Sema/SemaDecl.cpp

@@ -832,7 +832,7 @@ static bool isTagTypeWithMissingTag(Sema &SemaRef, LookupResult &Result,
                                     IdentifierInfo *&Name,
                                     SourceLocation NameLoc) {
   LookupResult R(SemaRef, Name, NameLoc, Sema::LookupTagName);
-  SemaRef.LookupParsedName(R, S, &SS);
+  SemaRef.LookupParsedName(R, S, &SS, /*ObjectType=*/QualType());
   if (TagDecl *Tag = R.getAsSingle<TagDecl>()) {
     StringRef FixItTagName;
     switch (Tag->getTagKind()) {
@@ -869,7 +869,7 @@ static bool isTagTypeWithMissingTag(Sema &SemaRef, LookupResult &Result,
 
     // Replace lookup results with just the tag decl.
     Result.clear(Sema::LookupTagName);
-    SemaRef.LookupParsedName(Result, S, &SS);
+    SemaRef.LookupParsedName(Result, S, &SS, /*ObjectType=*/QualType());
     return true;
   }
 
@@ -896,7 +896,8 @@ Sema::NameClassification Sema::ClassifyName(Scope *S, CXXScopeSpec &SS,
   }
 
   LookupResult Result(*this, Name, NameLoc, LookupOrdinaryName);
-  LookupParsedName(Result, S, &SS, !CurMethod);
+  LookupParsedName(Result, S, &SS, /*ObjectType=*/QualType(),
+                   /*AllowBuiltinCreation=*/!CurMethod);
 
   if (SS.isInvalid())
     return NameClassification::Error();

clang/lib/Sema/SemaDeclCXX.cpp

@@ -4517,7 +4517,7 @@ Sema::BuildMemInitializer(Decl *ConstructorD,
                               DS.getBeginLoc(), DS.getEllipsisLoc());
   } else {
     LookupResult R(*this, MemberOrBase, IdLoc, LookupOrdinaryName);
-    LookupParsedName(R, S, &SS);
+    LookupParsedName(R, S, &SS, /*ObjectType=*/QualType());
 
     TypeDecl *TyD = R.getAsSingle<TypeDecl>();
     if (!TyD) {
@@ -12262,7 +12262,7 @@ Decl *Sema::ActOnUsingDirective(Scope *S, SourceLocation UsingLoc,
 
   // Lookup namespace name.
   LookupResult R(*this, NamespcName, IdentLoc, LookupNamespaceName);
-  LookupParsedName(R, S, &SS);
+  LookupParsedName(R, S, &SS, /*ObjectType=*/QualType());
   if (R.isAmbiguous())
     return nullptr;
 
@@ -13721,7 +13721,7 @@ Decl *Sema::ActOnNamespaceAliasDef(Scope *S, SourceLocation NamespaceLoc,
 
   // Lookup the namespace name.
   LookupResult R(*this, Ident, IdentLoc, LookupNamespaceName);
-  LookupParsedName(R, S, &SS);
+  LookupParsedName(R, S, &SS, /*ObjectType=*/QualType());
 
   if (R.isAmbiguous())
     return nullptr;

clang/lib/Sema/SemaExpr.cpp

@@ -673,8 +673,9 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   // expressions of certain types in C++.
   if (getLangOpts().CPlusPlus &&
       (E->getType() == Context.OverloadTy ||
-       T->isDependentType() ||
-       T->isRecordType()))
+       // FIXME: This is a hack! We want the lvalue-to-rvalue conversion applied
+       // to pointer types even if the pointee type is dependent.
+       (T->isDependentType() && !T->isPointerType()) || T->isRecordType()))
     return E;
 
   // The C standard is actually really unclear on this point, and
@@ -2751,8 +2752,8 @@ Sema::ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
   if (isBoundsAttrContext() && !getLangOpts().CPlusPlus && S->isClassScope()) {
     // See if this is reference to a field of struct.
     LookupResult R(*this, NameInfo, LookupMemberName);
-    // LookupParsedName handles a name lookup from within anonymous struct.
-    if (LookupParsedName(R, S, &SS)) {
+    // LookupName handles a name lookup from within anonymous struct.
+    if (LookupName(R, S)) {
       if (auto *VD = dyn_cast<ValueDecl>(R.getFoundDecl())) {
         QualType type = VD->getType().getNonReferenceType();
         // This will eventually be translated into MemberExpr upon
@@ -2773,20 +2774,19 @@ Sema::ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
     // lookup to determine that it was a template name in the first place. If
     // this becomes a performance hit, we can work harder to preserve those
     // results until we get here but it's likely not worth it.
-    bool MemberOfUnknownSpecialization;
     AssumedTemplateKind AssumedTemplate;
-    if (LookupTemplateName(R, S, SS, QualType(), /*EnteringContext=*/false,
-                           MemberOfUnknownSpecialization, TemplateKWLoc,
+    if (LookupTemplateName(R, S, SS, /*ObjectType=*/QualType(),
+                           /*EnteringContext=*/false, TemplateKWLoc,
                            &AssumedTemplate))
       return ExprError();
 
-    if (MemberOfUnknownSpecialization ||
-        (R.getResultKind() == LookupResult::NotFoundInCurrentInstantiation))
+    if (R.wasNotFoundInCurrentInstantiation())
       return ActOnDependentIdExpression(SS, TemplateKWLoc, NameInfo,
                                         IsAddressOfOperand, TemplateArgs);
   } else {
     bool IvarLookupFollowUp = II && !SS.isSet() && getCurMethodDecl();
-    LookupParsedName(R, S, &SS, !IvarLookupFollowUp);
+    LookupParsedName(R, S, &SS, /*ObjectType=*/QualType(),
+                     /*AllowBuiltinCreation=*/!IvarLookupFollowUp);
 
     // If the result might be in a dependent base class, this is a dependent
     // id-expression.

clang/lib/Sema/SemaExprCXX.cpp

@@ -9157,7 +9157,7 @@ Sema::CheckMicrosoftIfExistsSymbol(Scope *S,
   // Do the redeclaration lookup in the current scope.
   LookupResult R(*this, TargetNameInfo, Sema::LookupAnyName,
                  RedeclarationKind::NotForRedeclaration);
-  LookupParsedName(R, S, &SS);
+  LookupParsedName(R, S, &SS, /*ObjectType=*/QualType());
   R.suppressDiagnostics();
 
   switch (R.getResultKind()) {