Reapply "[Clang] Implement resolution for CWG1835 (#92957, #98547)"

clang/docs/ReleaseNotes.rst

@@ -268,6 +268,9 @@ Resolutions to C++ Defect Reports
   by default.
   (`CWG2521: User-defined literals and reserved identifiers <https://cplusplus.github.io/CWG/issues/2521.html>`_).
 
+- Clang now correctly implements lookup for the terminal name of a member-qualified nested-name-specifier.
+  (`CWG1835: Dependent member lookup before < <https://cplusplus.github.io/CWG/issues/1835.html>`_).
+
 C Language Changes
 ------------------
 

clang/include/clang/AST/ExprCXX.h

@@ -3678,9 +3678,9 @@ class CXXUnresolvedConstructExpr final
 /// an implicit access if a qualifier is provided.
 class CXXDependentScopeMemberExpr final
     : public Expr,
-      private llvm::TrailingObjects<CXXDependentScopeMemberExpr,
-                                    ASTTemplateKWAndArgsInfo,
-                                    TemplateArgumentLoc, NamedDecl *> {
+      private llvm::TrailingObjects<
+          CXXDependentScopeMemberExpr, NestedNameSpecifierLoc, DeclAccessPair,
+          ASTTemplateKWAndArgsInfo, TemplateArgumentLoc> {
   friend class ASTStmtReader;
   friend class ASTStmtWriter;
   friend TrailingObjects;
@@ -3693,17 +3693,15 @@ class CXXDependentScopeMemberExpr final
   /// implicit accesses.
   QualType BaseType;
 
-  /// The nested-name-specifier that precedes the member name, if any.
-  /// FIXME: This could be in principle store as a trailing object.
-  /// However the performance impact of doing so should be investigated first.
-  NestedNameSpecifierLoc QualifierLoc;
-
   /// The member to which this member expression refers, which
   /// can be name, overloaded operator, or destructor.
   ///
   /// FIXME: could also be a template-id
   DeclarationNameInfo MemberNameInfo;
 
+  /// The location of the '->' or '.' operator.
+  SourceLocation OperatorLoc;
+
   // CXXDependentScopeMemberExpr is followed by several trailing objects,
   // some of which optional. They are in order:
   //
@@ -3723,8 +3721,16 @@ class CXXDependentScopeMemberExpr final
     return CXXDependentScopeMemberExprBits.HasTemplateKWAndArgsInfo;
   }
 
-  bool hasFirstQualifierFoundInScope() const {
-    return CXXDependentScopeMemberExprBits.HasFirstQualifierFoundInScope;
+  unsigned getNumUnqualifiedLookups() const {
+    return CXXDependentScopeMemberExprBits.NumUnqualifiedLookups;
+  }
+
+  unsigned numTrailingObjects(OverloadToken<NestedNameSpecifierLoc>) const {
+    return hasQualifier();
+  }
+
+  unsigned numTrailingObjects(OverloadToken<DeclAccessPair>) const {
+    return getNumUnqualifiedLookups();
   }
 
   unsigned numTrailingObjects(OverloadToken<ASTTemplateKWAndArgsInfo>) const {
@@ -3735,33 +3741,32 @@ class CXXDependentScopeMemberExpr final
     return getNumTemplateArgs();
   }
 
-  unsigned numTrailingObjects(OverloadToken<NamedDecl *>) const {
-    return hasFirstQualifierFoundInScope();
-  }
-
   CXXDependentScopeMemberExpr(const ASTContext &Ctx, Expr *Base,
                               QualType BaseType, bool IsArrow,
                               SourceLocation OperatorLoc,
                               NestedNameSpecifierLoc QualifierLoc,
                               SourceLocation TemplateKWLoc,
-                              NamedDecl *FirstQualifierFoundInScope,
+                              ArrayRef<DeclAccessPair> UnqualifiedLookups,
                               DeclarationNameInfo MemberNameInfo,
                               const TemplateArgumentListInfo *TemplateArgs);
 
-  CXXDependentScopeMemberExpr(EmptyShell Empty, bool HasTemplateKWAndArgsInfo,
-                              bool HasFirstQualifierFoundInScope);
+  CXXDependentScopeMemberExpr(EmptyShell Empty, bool HasQualifier,
+                              unsigned NumUnqualifiedLookups,
+                              bool HasTemplateKWAndArgsInfo);
 
 public:
   static CXXDependentScopeMemberExpr *
   Create(const ASTContext &Ctx, Expr *Base, QualType BaseType, bool IsArrow,
          SourceLocation OperatorLoc, NestedNameSpecifierLoc QualifierLoc,
-         SourceLocation TemplateKWLoc, NamedDecl *FirstQualifierFoundInScope,
+         SourceLocation TemplateKWLoc,
+         ArrayRef<DeclAccessPair> UnqualifiedLookups,
          DeclarationNameInfo MemberNameInfo,
          const TemplateArgumentListInfo *TemplateArgs);
 
   static CXXDependentScopeMemberExpr *
-  CreateEmpty(const ASTContext &Ctx, bool HasTemplateKWAndArgsInfo,
-              unsigned NumTemplateArgs, bool HasFirstQualifierFoundInScope);
+  CreateEmpty(const ASTContext &Ctx, bool HasQualifier,
+              unsigned NumUnqualifiedLookups, bool HasTemplateKWAndArgsInfo,
+              unsigned NumTemplateArgs);
 
   /// True if this is an implicit access, i.e. one in which the
   /// member being accessed was not written in the source.  The source
@@ -3786,34 +3791,35 @@ class CXXDependentScopeMemberExpr final
   bool isArrow() const { return CXXDependentScopeMemberExprBits.IsArrow; }
 
   /// Retrieve the location of the '->' or '.' operator.
-  SourceLocation getOperatorLoc() const {
-    return CXXDependentScopeMemberExprBits.OperatorLoc;
+  SourceLocation getOperatorLoc() const { return OperatorLoc; }
+
+  /// Determines whether this member expression had a nested-name-specifier
+  /// prior to the name of the member, e.g., x->Base::foo.
+  bool hasQualifier() const {
+    return CXXDependentScopeMemberExprBits.HasQualifier;
   }
 
-  /// Retrieve the nested-name-specifier that qualifies the member name.
-  NestedNameSpecifier *getQualifier() const {
-    return QualifierLoc.getNestedNameSpecifier();
+  /// If the member name was qualified, retrieves the nested-name-specifier
+  /// that precedes the member name, with source-location information.
+  NestedNameSpecifierLoc getQualifierLoc() const {
+    if (!hasQualifier())
+      return NestedNameSpecifierLoc();
+    return *getTrailingObjects<NestedNameSpecifierLoc>();
   }
 
-  /// Retrieve the nested-name-specifier that qualifies the member
-  /// name, with source location information.
-  NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
+  /// If the member name was qualified, retrieves the
+  /// nested-name-specifier that precedes the member name. Otherwise, returns
+  /// NULL.
+  NestedNameSpecifier *getQualifier() const {
+    return getQualifierLoc().getNestedNameSpecifier();
+  }
 
-  /// Retrieve the first part of the nested-name-specifier that was
-  /// found in the scope of the member access expression when the member access
-  /// was initially parsed.
-  ///
-  /// This function only returns a useful result when member access expression
-  /// uses a qualified member name, e.g., "x.Base::f". Here, the declaration
-  /// returned by this function describes what was found by unqualified name
-  /// lookup for the identifier "Base" within the scope of the member access
-  /// expression itself. At template instantiation time, this information is
-  /// combined with the results of name lookup into the type of the object
-  /// expression itself (the class type of x).
-  NamedDecl *getFirstQualifierFoundInScope() const {
-    if (!hasFirstQualifierFoundInScope())
-      return nullptr;
-    return *getTrailingObjects<NamedDecl *>();
+  /// Retrieve the declarations found by unqualified lookup for the first
+  /// component name of the nested-name-specifier, if any.
+  ArrayRef<DeclAccessPair> unqualified_lookups() const {
+    if (!getNumUnqualifiedLookups())
+      return std::nullopt;
+    return {getTrailingObjects<DeclAccessPair>(), getNumUnqualifiedLookups()};
   }
 
   /// Retrieve the name of the member that this expression refers to.

clang/include/clang/AST/Stmt.h

@@ -1040,18 +1040,19 @@ class alignas(void *) Stmt {
     LLVM_PREFERRED_TYPE(bool)
     unsigned IsArrow : 1;
 
+    /// True if this member expression used a nested-name-specifier to
+    /// refer to the member, e.g., "x->Base::f".
+    LLVM_PREFERRED_TYPE(bool)
+    unsigned HasQualifier : 1;
+
     /// Whether this member expression has info for explicit template
     /// keyword and arguments.
     LLVM_PREFERRED_TYPE(bool)
     unsigned HasTemplateKWAndArgsInfo : 1;
 
-    /// See getFirstQualifierFoundInScope() and the comment listing
-    /// the trailing objects.
-    LLVM_PREFERRED_TYPE(bool)
-    unsigned HasFirstQualifierFoundInScope : 1;
-
-    /// The location of the '->' or '.' operator.
-    SourceLocation OperatorLoc;
+    /// Number of declarations found by unqualified lookup for the
+    /// first component name of the nested-name-specifier.
+    unsigned NumUnqualifiedLookups;
   };
 
   class OverloadExprBitfields {

clang/include/clang/AST/UnresolvedSet.h

@@ -97,6 +97,10 @@ class UnresolvedSetImpl {
     decls().push_back(DeclAccessPair::make(D, AS));
   }
 
+  void addAllDecls(ArrayRef<DeclAccessPair> Other) {
+    append(iterator(Other.begin()), iterator(Other.end()));
+  }
+
   /// Replaces the given declaration with the new one, once.
   ///
   /// \return true if the set changed

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -912,9 +912,7 @@ def missing_template_arg_list_after_template_kw : Extension<
   "keyword">, InGroup<DiagGroup<"missing-template-arg-list-after-template-kw">>,
   DefaultError;
 
-def err_missing_dependent_template_keyword : Error<
-  "use 'template' keyword to treat '%0' as a dependent template name">;
-def warn_missing_dependent_template_keyword : ExtWarn<
+def ext_missing_dependent_template_keyword : ExtWarn<
   "use 'template' keyword to treat '%0' as a dependent template name">;
 
 def ext_extern_template : Extension<

clang/include/clang/Parse/Parser.h

@@ -1910,6 +1910,7 @@ class Parser : public CodeCompletionHandler {
   }
 
   bool diagnoseUnknownTemplateId(ExprResult TemplateName, SourceLocation Less);
+  bool isMissingTemplateKeywordBeforeScope(bool AnnotateInvalid);
   void checkPotentialAngleBracket(ExprResult &PotentialTemplateName);
   bool checkPotentialAngleBracketDelimiter(const AngleBracketTracker::Loc &,
                                            const Token &OpToken);
@@ -1970,7 +1971,7 @@ class Parser : public CodeCompletionHandler {
   //===--------------------------------------------------------------------===//
   // C++ Expressions
   ExprResult tryParseCXXIdExpression(CXXScopeSpec &SS, bool isAddressOfOperand,
-                                     Token &Replacement);
+                                     Token *Replacement = nullptr);
 
   ExprResult tryParseCXXPackIndexingExpression(ExprResult PackIdExpression);
   ExprResult ParseCXXPackIndexingExpression(ExprResult PackIdExpression);
@@ -2745,7 +2746,7 @@ class Parser : public CodeCompletionHandler {
   /// Determine whether the current token sequence might be
   ///   '<' template-argument-list '>'
   /// rather than a less-than expression.
-  TPResult isTemplateArgumentList(unsigned TokensToSkip);
+  TPResult isTemplateArgumentList(unsigned TokensToSkip, TemplateNameKind TNK);
 
   /// Determine whether an '(' after an 'explicit' keyword is part of a C++20
   /// 'explicit(bool)' declaration, in earlier language modes where that is an
@@ -2768,6 +2769,7 @@ class Parser : public CodeCompletionHandler {
   TPResult TryParseTypeofSpecifier();
   TPResult TryParseProtocolQualifiers();
   TPResult TryParsePtrOperatorSeq();
+  TPResult TryParseNonConversionOperatorId();
   TPResult TryParseOperatorId();
   TPResult TryParseInitDeclaratorList(bool MayHaveTrailingReturnType = false);
   TPResult TryParseDeclarator(bool mayBeAbstract, bool mayHaveIdentifier = true,
@@ -3382,15 +3384,11 @@ class Parser : public CodeCompletionHandler {
   BaseResult ParseBaseSpecifier(Decl *ClassDecl);
   AccessSpecifier getAccessSpecifierIfPresent() const;
 
-  bool ParseUnqualifiedIdTemplateId(CXXScopeSpec &SS,
-                                    ParsedType ObjectType,
-                                    bool ObjectHadErrors,
-                                    SourceLocation TemplateKWLoc,
-                                    IdentifierInfo *Name,
-                                    SourceLocation NameLoc,
-                                    bool EnteringContext,
-                                    UnqualifiedId &Id,
-                                    bool AssumeTemplateId);
+  bool ParseUnqualifiedIdTemplateId(
+      CXXScopeSpec &SS, ParsedType ObjectType, bool ObjectHadErrors,
+      SourceLocation TemplateKWLoc, SourceLocation TildeLoc,
+      IdentifierInfo *Name, SourceLocation NameLoc, bool EnteringContext,
+      UnqualifiedId &Id, bool AssumeTemplateId);
   bool ParseUnqualifiedIdOperator(CXXScopeSpec &SS, bool EnteringContext,
                                   ParsedType ObjectType,
                                   UnqualifiedId &Result);

clang/include/clang/Sema/DeclSpec.h

@@ -75,6 +75,7 @@ class CXXScopeSpec {
   SourceRange Range;
   NestedNameSpecifierLocBuilder Builder;
   ArrayRef<TemplateParameterList *> TemplateParamLists;
+  ArrayRef<DeclAccessPair> UnqualifiedLookups;
 
 public:
   SourceRange getRange() const { return Range; }
@@ -91,6 +92,13 @@ class CXXScopeSpec {
     return TemplateParamLists;
   }
 
+  void setUnqualifiedLookups(ArrayRef<DeclAccessPair> Found) {
+    UnqualifiedLookups = Found;
+  }
+  ArrayRef<DeclAccessPair> getUnqualifiedLookups() const {
+    return UnqualifiedLookups;
+  }
+
   /// Retrieve the representation of the nested-name-specifier.
   NestedNameSpecifier *getScopeRep() const {
     return Builder.getRepresentation();

clang/include/clang/Sema/Lookup.h

@@ -483,11 +483,15 @@ class LookupResult {
     ResultKind = Found;
   }
 
+  void addAllDecls(ArrayRef<DeclAccessPair> Other) {
+    Decls.addAllDecls(Other);
+    ResultKind = Found;
+  }
+
   /// Add all the declarations from another set of lookup
   /// results.
   void addAllDecls(const LookupResult &Other) {
-    Decls.append(Other.Decls.begin(), Other.Decls.end());
-    ResultKind = Found;
+    addAllDecls(Other.Decls.pairs());
   }
 
   /// Determine whether no result was found because we could not