C++: Fix variable template parsing in expression

Fix parser to not fail on TemplateId without parentheses, for example:
int i = foo<int> + foo<char>;

This fixes std::pair structure parsing in MSVC headers and find Usages
to work with pair->first and pair->second.

Change-Id: Ic300ea99d44a749705430d5eb47b2744715af995
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

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

@@ -5066,12 +5066,6 @@ bool Parser::parseNameId(NameAST *&name)
     case T_CONST_CAST:
         rewind(start);
         return parseName(name, false);
-
-    default:
-        if (tok().isLiteral() || tok().isPunctuationOrOperator()) {
-            rewind(start);
-            return parseName(name, false);
-        }
     } // switch
 
     return true;

tests/auto/cplusplus/ast/tst_ast.cpp

@@ -173,6 +173,7 @@ private slots:
     //! "template<class ...Args> class T : Args... {};"
     void cpp11_variadic_inheritance();
     void cpp11_attributes();
+    void variableTemplatesInExpression();
 
     // Q_PROPERTY
     void cpp_qproperty();
@@ -1354,6 +1355,19 @@ void tst_AST::cpp11_attributes()
     QVERIFY(attr != nullptr);
 }
 
+void tst_AST::variableTemplatesInExpression()
+{
+    QSharedPointer<TranslationUnit> unit(parseDeclaration("int i = t<int> + t<char>;",
+                                                         false, false, true));
+    AST *ast = unit->ast();
+    QVERIFY(ast != nullptr);
+
+    QCOMPARE(diag.errorCount, 0);
+
+    DeclarationAST *d = ast->asDeclaration();
+    QVERIFY(d != nullptr);
+}
+
 void tst_AST::if_constexpr()
 {
     QSharedPointer<TranslationUnit> unit(parseStatement("if constexpr (a) b;",true));

tests/auto/cplusplus/findusages/tst_findusages.cpp

@@ -125,6 +125,7 @@ private Q_SLOTS:
     void templatePartialSpecialization();
     void templatePartialSpecialization_2();
     void template_SFINAE_1();
+    void variableTemplateInExpression();
 };
 
 void tst_FindUsages::dump(const QList<Usage> &usages) const
@@ -1580,5 +1581,48 @@ int main(){
     QCOMPARE(find.usages().size(), 2);
 }
 
+void tst_FindUsages::variableTemplateInExpression()
+{
+    const QByteArray src =
+R"(
+struct S{int value;};
+template<class T> constexpr int foo = sizeof(T);
+template<class T1, class T2>
+struct pair{
+    pair() noexcept(foo<T1> + foo<T2>){}
+    T1 first;
+    T2 second;
+};
+int main(){
+    pair<int, S> pair;
+    pair.second.value;
+}
+)";
+
+    Document::Ptr doc = Document::create("variableTemplateInExpression");
+    doc->setUtf8Source(src);
+    doc->parse();
+    doc->check();
+
+    QVERIFY(doc->diagnosticMessages().isEmpty());
+    QVERIFY(doc->globalSymbolCount()>=1);
+
+    Snapshot snapshot;
+    snapshot.insert(doc);
+
+    Class *s = doc->globalSymbolAt(0)->asClass();
+    QVERIFY(s);
+    QCOMPARE(s->name()->identifier()->chars(), "S");
+    QCOMPARE(s->memberCount(), 1);
+
+    Declaration *sv = s->memberAt(0)->asDeclaration();
+    QVERIFY(sv);
+    QCOMPARE(sv->name()->identifier()->chars(), "value");
+
+    FindUsages find(src, doc, snapshot);
+    find(sv);
+    QCOMPARE(find.usages().size(), 2);
+}
+
 QTEST_APPLESS_MAIN(tst_FindUsages)
 #include "tst_findusages.moc"