C++: fix code completion for decltyped type

example:
struct Foo { int bar; };
Foo foo() { return Foo; }
typedef decltype(foo()) TypedefedFooWithDecltype;
void fun()
{
  decltype(foo()) decltypeFoo;
  decltypeFoo.;// code completion should work here

  TypedefedFooWithDecltype typedefedFooWithDecltype;
  typedefedFooWithDecltype.;// code completion should work here
}

Started-by: Przemyslaw Gorszkowski <pgorszkowski@gmail.com>
Task-number: QTCREATORBUG-14483
Change-Id: I296ceed9d896c68cf0651265afb08a1fc42f9a68
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/libs/3rdparty/cplusplus/Bind.cpp

@@ -1921,9 +1921,22 @@ bool Bind::visit(SimpleDeclarationAST *ast)
         methodKey = methodKeyForInvokableToken(tokenKind(ast->qt_invokable_token));
 
     // unsigned qt_invokable_token = ast->qt_invokable_token;
+    unsigned declTypeStartOfExpression = 0;
+    unsigned declTypeEndOfExpression = 0;
+    bool isTypedef = false;
     FullySpecifiedType type;
     for (SpecifierListAST *it = ast->decl_specifier_list; it; it = it->next) {
         type = this->specifier(it->value, type);
+        if (type.isTypedef())
+            isTypedef = true;
+
+        type.setTypedef(isTypedef);
+        if (type.isDecltype()) {
+            if (DecltypeSpecifierAST *decltypeSpec = it->value->asDecltypeSpecifier()) {
+                declTypeStartOfExpression = decltypeSpec->expression->firstToken();
+                declTypeEndOfExpression = decltypeSpec->expression->lastToken();
+            }
+        }
     }
 
     List<Symbol *> **symbolTail = &ast->symbols;
@@ -1982,6 +1995,9 @@ bool Bind::visit(SimpleDeclarationAST *ast)
                 unsigned endOfExpression = initializer->lastToken();
                 decl->setInitializer(asStringLiteral(startOfExpression, endOfExpression));
             }
+        } else if (declTy.isDecltype()) {
+            decl->setInitializer(asStringLiteral(declTypeStartOfExpression,
+                                                 declTypeEndOfExpression));
         }
 
         if (_scope->isClass()) {
@@ -3028,6 +3044,7 @@ bool Bind::visit(TypeofSpecifierAST *ast)
 bool Bind::visit(DecltypeSpecifierAST *ast)
 {
     _type = this->expression(ast->expression);
+    _type.setDecltype(true);
     return false;
 }
 

src/libs/3rdparty/cplusplus/FullySpecifiedType.cpp

@@ -100,6 +100,12 @@ bool FullySpecifiedType::isAuto() const
 void FullySpecifiedType::setAuto(bool isAuto)
 { f._isAuto = isAuto; }
 
+bool FullySpecifiedType::isDecltype() const
+{ return f._isDecltype; }
+
+void FullySpecifiedType::setDecltype(bool isDecltype)
+{ f._isDecltype = isDecltype; }
+
 bool FullySpecifiedType::isRegister() const
 { return f._isRegister; }
 

src/libs/3rdparty/cplusplus/FullySpecifiedType.h

@@ -58,6 +58,9 @@ public:
     bool isAuto() const;
     void setAuto(bool isAuto);
 
+    bool isDecltype() const;
+    void setDecltype(bool isDecltype);
+
     bool isRegister() const;
     void setRegister(bool isRegister);
 
@@ -125,6 +128,7 @@ private:
         // storage class specifiers
         unsigned _isFriend: 1;
         unsigned _isAuto: 1;
+        unsigned _isDecltype: 1;
         unsigned _isRegister: 1;
         unsigned _isStatic: 1;
         unsigned _isExtern: 1;