GLSL: Avoid infinite loop at error recovery

For error recovery additional tokens are tried to produce a valid
grammar rule.

For the specific case in the bug report

    for(int x=0; x y

the two consecutive identifiers in the end triggered an infinite loop
since the identifier token is also part of those additional tokens that
are tried.

Circumvent this by trying a more conservative list of tokens on the
second try.

Done-by: Erik Verbruggen
Change-Id: I271dddecf947a06ed3af5f9955ee630441533342
Task-number: QTCREATORBUG-18967
Reviewed-by: Erik Verbruggen <erik.verbruggen@qt.io>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/libs/glsl/glsl.g

@@ -519,9 +519,13 @@ AST *Parser::parse(int startToken)
     _recovered = false;
     _tos = -1;
     _startToken.kind = startToken;
+    int recoveryAttempts = 0;
+
 
     do {
-    again:
+        recoveryAttempts = 0;
+
+    againAfterRecovery:
         if (unsigned(++_tos) == _stateStack.size()) {
             _stateStack.resize(_tos * 2);
             _locationStack.resize(_tos * 2);
@@ -564,6 +568,7 @@ AST *Parser::parse(int startToken)
             reduce(ruleno);
             action = nt_action(_stateStack[_tos], lhs[ruleno] - TERMINAL_COUNT);
         } else if (action == 0) {
+            ++recoveryAttempts;
             const int line = _tokens[yyloc].line + 1;
             QString message = QLatin1String("Syntax error");
             if (yytoken != -1) {
@@ -574,7 +579,7 @@ AST *Parser::parse(int startToken)
             for (; _tos; --_tos) {
                 const int state = _stateStack[_tos];
 
-                static int tks[] = {
+                static int tks1[] = {
                     T_RIGHT_BRACE, T_RIGHT_PAREN, T_RIGHT_BRACKET,
                     T_SEMICOLON, T_COLON, T_COMMA,
                     T_NUMBER, T_TYPE_NAME, T_IDENTIFIER,
@@ -582,6 +587,16 @@ AST *Parser::parse(int startToken)
                     T_WHILE,
                     0
                 };
+                static int tks2[] = {
+                    T_RIGHT_BRACE, T_RIGHT_PAREN, T_RIGHT_BRACKET,
+                    T_SEMICOLON, T_COLON, T_COMMA,
+                    0
+                };
+                int *tks;
+                if (recoveryAttempts < 2)
+                    tks = tks1;
+                else
+                    tks = tks2; // Avoid running into an endless loop for e.g.: for(int x=0; x y
 
                 for (int *tptr = tks; *tptr; ++tptr) {
                     const int next = t_action(state, *tptr);
@@ -604,7 +619,7 @@ AST *Parser::parse(int startToken)
                         yytoken = -1;
 
                         action = next;
-                        goto again;
+                        goto againAfterRecovery;
                     }
                 }
             }