[DO NOT SUBMIT] Provide results with '.' to '->' corrections in completion

[ilya-biryukov]

Summary

Not intended to be submitted, this is a suggestion on how to make the
code in D41537 easier.

include/clang/Sema/Sema.h

public:
   void CodeCompleteDeclSpec(Scope *S, DeclSpec &DS,
                             bool AllowNonIdentifiers,
                             bool AllowNestedNameSpecifiers);
 
   struct CodeCompleteExpressionData;
   void CodeCompleteExpression(Scope *S,
                               const CodeCompleteExpressionData &Data);
   void CodeCompleteMemberReferenceExpr(Scope *S, Expr *Base,
-                                       SourceLocation OpLoc, bool IsArrow,
-                                       bool IsBaseExprStatement);
+                                       Expr *OtherOpBase, SourceLocation OpLoc,
+                                       bool IsArrow, bool IsBaseExprStatement);
   void CodeCompletePostfixExpression(Scope *S, ExprResult LHS);
   void CodeCompleteTag(Scope *S, unsigned TagSpec);
   void CodeCompleteTypeQualifiers(DeclSpec &DS);
   void CodeCompleteFunctionQualifiers(DeclSpec &DS, Declarator &D,
                                       const VirtSpecifiers *VS = nullptr);
   void CodeCompleteBracketDeclarator(Scope *S);
   void CodeCompleteCase(Scope *S);
   void CodeCompleteCall(Scope *S, Expr *Fn, ArrayRef<Expr *> Args);

lib/Parse/ParseExpr.cpp

case tok::period: {
       // postfix-expression: p-e '->' template[opt] id-expression
       // postfix-expression: p-e '.' template[opt] id-expression
       tok::TokenKind OpKind = Tok.getKind();
       SourceLocation OpLoc = ConsumeToken();  // Eat the "." or "->" token.
 
       CXXScopeSpec SS;
       ParsedType ObjectType;
       bool MayBePseudoDestructor = false;
+      Expr* OrigLHS = !LHS.isInvalid() ? LHS.get() : nullptr;
       if (getLangOpts().CPlusPlus && !LHS.isInvalid()) {
-        Expr *Base = LHS.get();
+        Expr *Base = OrigLHS;
         const Type* BaseType = Base->getType().getTypePtrOrNull();
         if (BaseType && Tok.is(tok::l_paren) &&
             (BaseType->isFunctionType() ||
              BaseType->isSpecificPlaceholderType(BuiltinType::BoundMember))) {
           Diag(OpLoc, diag::err_function_is_not_record)
               << OpKind << Base->getSourceRange()
               << FixItHint::CreateRemoval(OpLoc);
           return ParsePostfixExpressionSuffix(Base);
         }
 
         LHS = Actions.ActOnStartCXXMemberReference(getCurScope(), Base,
                                                    OpLoc, OpKind, ObjectType,
                                                    MayBePseudoDestructor);
         if (LHS.isInvalid())
           break;
 
         ParseOptionalCXXScopeSpecifier(SS, ObjectType, 
                                        /*EnteringContext=*/false,
                                        &MayBePseudoDestructor);
         if (SS.isNotEmpty())
           ObjectType = nullptr;
       }
 
       if (Tok.is(tok::code_completion)) {
+        tok::TokenKind CorrectedOpKind =
+            OpKind == tok::arrow ? tok::period : tok::arrow;
+        ExprResult CorrectedLHS(/*IsInvalid=*/true);
+        if (getLangOpts().CPlusPlus && OrigLHS) {
+          ParsedType CorrectedObjectType;
+          CorrectedLHS = Actions.ActOnStartCXXMemberReference(
+              getCurScope(), OrigLHS, OpLoc, CorrectedOpKind, ObjectType,
+              MayBePseudoDestructor);
+        }
+
+        Expr *Base = LHS.get();
+        Expr *CorrectedBase = CorrectedLHS.get();
+
         // Code completion for a member access expression.
-        if (Expr *Base = LHS.get())
-          Actions.CodeCompleteMemberReferenceExpr(
-              getCurScope(), Base, OpLoc, OpKind == tok::arrow,
-              ExprStatementTokLoc == Base->getLocStart());
+            getCurScope(), Base, CorrectedBase, OpLoc, OpKind == tok::arrow,
+            Base && ExprStatementTokLoc == Base->getLocStart());
 
         cutOffParsing();
         return ExprError();
       }
 
       if (MayBePseudoDestructor && !LHS.isInvalid()) {
         LHS = ParseCXXPseudoDestructor(LHS.get(), OpLoc, OpKind, SS, 
                                        ObjectType);

lib/Sema/SemaCodeComplete.cpp

if (!Results.empty()) {
 
       if (IsDependent)
         Results.AddResult(CodeCompletionResult("template"));
     }
   }
 }
 
 void Sema::CodeCompleteMemberReferenceExpr(Scope *S, Expr *Base,
+                                           Expr *OtherOpBase,
                                            SourceLocation OpLoc, bool IsArrow,
                                            bool IsBaseExprStatement) {
   if (!Base || !CodeCompleter)
     return;
-  
   ExprResult ConvertedBase = PerformMemberExprBaseConversion(Base, IsArrow);
   if (ConvertedBase.isInvalid())
     return;
-  Base = ConvertedBase.get();
-  
-  QualType BaseType = Base->getType();
-
-  if (IsArrow) {
-    if (const PointerType *Ptr = BaseType->getAs<PointerType>())
-      BaseType = Ptr->getPointeeType();
-    else if (BaseType->isObjCObjectPointerType())
-      /*Do nothing*/ ;
-    else
-      return;
-  }
-  
+  QualType ConvertedBaseType = ConvertedBase.get()->getType();
   enum CodeCompletionContext::Kind contextKind;
-  
   if (IsArrow) {
     contextKind = CodeCompletionContext::CCC_ArrowMemberAccess;
-  }
-  else {
-    if (BaseType->isObjCObjectPointerType() ||
-        BaseType->isObjCObjectOrInterfaceType()) {
+  } else {
+    if (ConvertedBaseType->isObjCObjectPointerType() ||
+        ConvertedBaseType->isObjCObjectOrInterfaceType()) {
       contextKind = CodeCompletionContext::CCC_ObjCPropertyAccess;
-    }
-    else {
+    } else {
       contextKind = CodeCompletionContext::CCC_DotMemberAccess;
     }
   }
 
-  CodeCompletionContext CCContext(contextKind, BaseType);
+  CodeCompletionContext CCContext(contextKind, ConvertedBaseType);
   ResultBuilder Results(*this, CodeCompleter->getAllocator(),
-                        CodeCompleter->getCodeCompletionTUInfo(),
-                        CCContext,
+                        CodeCompleter->getCodeCompletionTUInfo(), CCContext,
                         &ResultBuilder::IsMember);
-  Results.EnterNewScope();
+
+  auto DoCompletion = [&](Expr *Base, bool IsArrow) -> bool {
+    if (!Base)
+      return false;
+
+    ExprResult ConvertedBase = PerformMemberExprBaseConversion(Base, IsArrow);
+    if (ConvertedBase.isInvalid())
+      return false;
+    Base = ConvertedBase.get();
+
+    QualType BaseType = Base->getType();
+
+    if (IsArrow) {
+      if (const PointerType *Ptr = BaseType->getAs<PointerType>())
+        BaseType = Ptr->getPointeeType();
+      else if (BaseType->isObjCObjectPointerType())
+        /*Do nothing*/;
+      else
+        return false;
+    }
+
     if (const RecordType *Record = BaseType->getAs<RecordType>()) {
       AddRecordMembersCompletionResults(*this, Results, S, BaseType,
                                         Record->getDecl());
-  } else if (const auto *TST = BaseType->getAs<TemplateSpecializationType>()) {
+    } else if (const auto *TST =
+                   BaseType->getAs<TemplateSpecializationType>()) {
       TemplateName TN = TST->getTemplateName();
       if (const auto *TD =
               dyn_cast_or_null<ClassTemplateDecl>(TN.getAsTemplateDecl())) {
         CXXRecordDecl *RD = TD->getTemplatedDecl();
         AddRecordMembersCompletionResults(*this, Results, S, BaseType, RD);
       }
     } else if (const auto *ICNT = BaseType->getAs<InjectedClassNameType>()) {
       if (auto *RD = ICNT->getDecl())
         AddRecordMembersCompletionResults(*this, Results, S, BaseType, RD);
     } else if (!IsArrow && BaseType->isObjCObjectPointerType()) {
       // Objective-C property reference.
       AddedPropertiesSet AddedProperties;
 
       if (const ObjCObjectPointerType *ObjCPtr =
               BaseType->getAsObjCInterfacePointerType()) {
         // Add property results based on our interface.
         assert(ObjCPtr && "Non-NULL pointer guaranteed above!");
         AddObjCProperties(CCContext, ObjCPtr->getInterfaceDecl(), true,
                           /*AllowNullaryMethods=*/true, CurContext,
                           AddedProperties, Results, IsBaseExprStatement);
       }
 
       // Add properties from the protocols in a qualified interface.
       for (auto *I : BaseType->getAs<ObjCObjectPointerType>()->quals())
         AddObjCProperties(CCContext, I, true, /*AllowNullaryMethods=*/true,
                           CurContext, AddedProperties, Results,
                           IsBaseExprStatement);
     } else if ((IsArrow && BaseType->isObjCObjectPointerType()) ||
                (!IsArrow && BaseType->isObjCObjectType())) {
       // Objective-C instance variable access.
       ObjCInterfaceDecl *Class = nullptr;
-    if (const ObjCObjectPointerType *ObjCPtr
-                                    = BaseType->getAs<ObjCObjectPointerType>())
+      if (const ObjCObjectPointerType *ObjCPtr =
+              BaseType->getAs<ObjCObjectPointerType>())
         Class = ObjCPtr->getInterfaceDecl();
       else
         Class = BaseType->getAs<ObjCObjectType>()->getInterface();
-    
       // Add all ivars from this class and its superclasses.
       if (Class) {
         CodeCompletionDeclConsumer Consumer(Results, CurContext);
         Results.setFilter(&ResultBuilder::IsObjCIvar);
         LookupVisibleDecls(
             Class, LookupMemberName, Consumer, CodeCompleter->includeGlobals(),
             /*IncludeDependentBases=*/false, CodeCompleter->loadExternal());
       }
     }
-  
     // FIXME: How do we cope with isa?
-  
+    return true;
+  };
+  Results.EnterNewScope();
+  bool CompletionSucceded =
+      DoCompletion(Base, IsArrow) | DoCompletion(OtherOpBase, !IsArrow);
   Results.ExitScope();
 
+  if (!CompletionSucceded)
+    return;
+
   // Hand off the results found for code completion.
-  HandleCodeCompleteResults(this, CodeCompleter, 
-                            Results.getCompletionContext(),
-                            Results.data(),Results.size());
+  HandleCodeCompleteResults(this, CodeCompleter, Results.getCompletionContext(),
+                            Results.data(), Results.size());
 }
 
 void Sema::CodeCompleteObjCClassPropertyRefExpr(Scope *S,
                                                 IdentifierInfo &ClassName,
                                                 SourceLocation ClassNameLoc,
                                                 bool IsBaseExprStatement) {
   IdentifierInfo *ClassNamePtr = &ClassName;
   ObjCInterfaceDecl *IFace = getObjCInterfaceDecl(ClassNamePtr, ClassNameLoc);