C: Parser: Support parsing of c99 designated initializers

In case:

    int a[6] = { [4] = 29, [2] = 15 };
    struct point { int x, y; };
    struct point p = { .y = 3, .x = 2 };

Grammar change when c99 language feature is enabled:
old grammar:

    braced-init-list :: '{' initializer-list '}'

new grammar:

    braced-init-list :: '{' designated-initializer-list '}'
    designated-initializer-list :: designated-initializer (',' designated-initializer )*
    designated-initializer :: designator* initializer-clause
    designator :: '.' identifier
                | '[' constant-expression ']'

Task-number: QTCREATORBUG-1902
Change-Id: Ib99d6f553f8d0f50ba3eff86f3a2e86d73372426
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

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

@@ -2664,7 +2664,7 @@ bool Parser::parseInitializerList0x(ExpressionListAST *&node)
     ExpressionListAST **expression_list_ptr = &node;
     ExpressionAST *expression = 0;
 
-    if (parseInitializerClause0x(expression)) {
+    if (parseDesignatedInitializer(expression)) {
         *expression_list_ptr = new (_pool) ExpressionListAST;
         (*expression_list_ptr)->value = expression;
         expression_list_ptr = &(*expression_list_ptr)->next;
@@ -2675,7 +2675,7 @@ bool Parser::parseInitializerList0x(ExpressionListAST *&node)
         while (LA() == T_COMMA && LA(2) != T_RBRACE) {
             consumeToken(); // consume T_COMMA
 
-            if (parseInitializerClause0x(expression)) {
+            if (parseDesignatedInitializer(expression)) {
                 *expression_list_ptr = new (_pool) ExpressionListAST;
                 (*expression_list_ptr)->value = expression;
 
@@ -5484,6 +5484,50 @@ bool Parser::lookAtObjCSelector() const
     return false;
 }
 
+// designated-initializer ::= designator* T_EQUAL initializer-clause
+//
+bool Parser::parseDesignatedInitializer(ExpressionAST *&node)
+{
+    DEBUG_THIS_RULE();
+    if (!_languageFeatures.c99Enabled || (LA() != T_DOT && LA() != T_LBRACKET))
+        return parseInitializerClause0x(node);
+
+    DesignatedInitializerAST *ast = new (_pool) DesignatedInitializerAST;
+    DesignatorListAST **designator_list_ptr = &ast->designator_list;
+    DesignatorAST *designator = 0;
+    while (parseDesignator(designator)) {
+        *designator_list_ptr = new (_pool) DesignatorListAST;
+        (*designator_list_ptr)->value = designator;
+        designator_list_ptr = &(*designator_list_ptr)->next;
+    }
+    match(T_EQUAL, &ast->equal_token);
+    parseInitializerClause0x(ast->initializer);
+    node = ast;
+    return true;
+}
+
+// designator ::= T_DOT T_IDENTIFIER
+//                T_LBRACKET constant-expression T_BRACKET
+//
+bool Parser::parseDesignator(DesignatorAST *&node)
+{
+    DesignatorAST *ast = new (_pool) DesignatorAST;
+    if (LA() == T_DOT) {
+        ast->type = DesignatorAST::Dot;
+        ast->u.dot.dot_token = consumeToken();
+        match(T_IDENTIFIER, &ast->u.dot.identifier_token);
+    } else if (LA() == T_LBRACKET) {
+        ast->type = DesignatorAST::Bracket;
+        ast->u.bracket.lbracket_token = consumeToken();
+        parseConstantExpression(ast->u.bracket.expression);
+        match(T_RBRACKET, &ast->u.bracket.rbracket_token);
+    } else {
+        return false;
+    }
+    node = ast;
+    return true;
+}
+
 // objc-class-declaraton ::= T_AT_CLASS (T_IDENTIFIER @ T_COMMA) T_SEMICOLON
 //
 bool Parser::parseObjCClassForwardDeclaration(DeclarationAST *&node)