Fix #14613 Crash in compilePrecedence2() (function called requires) (cppcheck-opensource#8361)

Co-authored-by: chrchr-github <noreply@github.com>

Author: chrchr-github

lib/tokenlist.cpp

@@ -1058,10 +1058,12 @@ static void compilePrecedence2(Token *&tok, AST_state& state)
             else
                 compileUnaryOp(tok, state, compileExpression);
             tok = tok2->link()->next();
-        } else if (Token::simpleMatch(tok->previous(), "requires {")
-                   || (Token::simpleMatch(tok->previous(), ")")
+        } else if ((Token::simpleMatch(tok->tokAt(-1), "requires {") && tok->tokAt(-1)->isKeyword())
+                   || (Token::simpleMatch(tok->tokAt(-1), ")")
                        && tok->linkAt(-1)
-                       && Token::simpleMatch(tok->linkAt(-1)->previous(), "requires ("))) {
+                       && Token::simpleMatch(tok->linkAt(-1)->tokAt(-1), "requires (") && tok->linkAt(-1)->tokAt(-1)->isKeyword())) {
+            if (!tok->link())
+                throw InternalError(tok, "Syntax error, token has no link.", InternalError::AST);
             tok->astOperand1(state.op.top());
             state.op.pop();
             state.op.push(tok);

test/testtokenize.cpp

@@ -8332,6 +8332,12 @@ class TestTokenizer : public TestFixture {
 
     void cppKeywordInCSource() {
         ASSERT_NO_THROW(tokenizeAndStringify("int throw() {}", dinit(TokenizeOptions, $.cpp = false)));
+
+        const char code[] = "void requires(const char*);\n" // #14613
+                            "void f() { requires(\"abc\"); }\n";
+        ASSERT_NO_THROW(tokenizeAndStringify(code, dinit(TokenizeOptions, $.cpp = false)));
+        ASSERT_NO_THROW(tokenizeAndStringify(code, dinit(TokenizeOptions, $.cpp = true, $.cppstd = Standards::CPP17)));
+        ASSERT_THROW_INTERNAL(tokenizeAndStringify(code, dinit(TokenizeOptions, $.cpp = true, $.cppstd = Standards::CPP20)), AST);
     }
 
     void cppcast() {