Don't crash on C++23 code (#4771)

Author: chrchr-github

lib/tokenlist.cpp

@@ -1598,7 +1598,7 @@ static Token * createAstAtToken(Token *tok, bool cpp)
                 semicolon2->astOperand2(state3.op.top());
             semicolon1->astOperand2(semicolon2);
         } else {
-            if (!cpp || !Token::simpleMatch(state2.op.top(), ":"))
+            if (!cpp || state2.op.empty() || !Token::simpleMatch(state2.op.top(), ":"))
                 throw InternalError(tok, "syntax error", InternalError::SYNTAX);
 
             semicolon1->astOperand2(state2.op.top());

test/testtokenize.cpp

@@ -434,6 +434,7 @@ class TestTokenizer : public TestFixture {
         TEST_CASE(noCrash4);
         TEST_CASE(noCrash5); // #10603
         TEST_CASE(noCrash6); // #10212
+        TEST_CASE(noCrash7);
 
         // --check-config
         TEST_CASE(checkConfiguration);
@@ -7357,6 +7358,12 @@ class TestTokenizer : public TestFixture {
                                              "struct c<a<e, d...>, true> {};\n"));
     }
 
+    void noCrash7() {
+        ASSERT_THROW(tokenizeAndStringify("void g() {\n"// TODO: don't throw
+                                          "    for (using T = int; (T)false;) {}\n" // C++23 P2360R0: Extend init-statement to allow alias-declaration
+                                          "}\n"), InternalError);
+    }
+
     void checkConfig(const char code[]) {
         errout.str("");