[clang-format] Fix requires related crash

[HazardyKnusperkeks]

Summary

In the presence of pp branches we parse the token stream multiple times. Thus the token already has the type set. It's best just not to assert on any type in the parser.

Fixes https://github.com/llvm/llvm-project/issues/54019

[curdeius]

LGTM. But your test case is far from the reproduce in the issue report, so please confirm with @owenpan.

[owenpan]

In D120512#3344027, @curdeius wrote:

LGTM. But your test case is far from the reproduce in the issue report, so please confirm with @owenpan.

See here.

[HazardyKnusperkeks]

Changed test.

clang/lib/Format/UnwrappedLineParser.cpp

 /// \pre We need to be on the next token after the requires keyword.
 /// \sa parseRequiresExpression
 ///
 /// Returns if it either has finished parsing the clause, or it detects, that
 /// the clause is incorrect.
 void UnwrappedLineParser::parseRequiresClause(FormatToken *RequiresToken) {
   assert(FormatTok->getPreviousNonComment() == RequiresToken);
   assert(RequiresToken->is(tok::kw_requires) && "'requires' expected");
-  assert(RequiresToken->getType() == TT_Unknown);
 
   // If there is no previous token, we are within a requires expression,
   // otherwise we will always have the template or function declaration in front
   // of it.
   bool InRequiresExpression =
       !RequiresToken->Previous ||
       RequiresToken->Previous->is(TT_RequiresExpressionLBrace);
 

 /// \pre We need to be on the next token after the requires keyword.
 /// \sa parseRequiresClause
 ///
 /// Returns if it either has finished parsing the expression, or it detects,
 /// that the expression is incorrect.
 void UnwrappedLineParser::parseRequiresExpression(FormatToken *RequiresToken) {
   assert(FormatTok->getPreviousNonComment() == RequiresToken);
   assert(RequiresToken->is(tok::kw_requires) && "'requires' expected");
-  assert(RequiresToken->getType() == TT_Unknown);
 
   RequiresToken->setFinalizedType(TT_RequiresExpression);
 
   if (FormatTok->is(tok::l_paren)) {
     FormatTok->setFinalizedType(TT_RequiresExpressionLParen);
     parseParens();
   }
 

clang/unittests/Format/FormatTest.cpp

 TEST_F(FormatTest, RequiresClauses) {
   verifyFormat("struct [[nodiscard]] zero_t {\n"
                "  template <class T>\n"
                "    requires requires { number_zero_v<T>; }\n"
                "  [[nodiscard]] constexpr operator T() const {\n"
                "    return number_zero_v<T>;\n"
                "  }\n"
                "};");
+
+  // Not a clause, but we once hit an assert.
+  verifyFormat("#if 0\n"
+               "#else\n"
+               "foo();\n"
+               "#endif\n"
+               "bar(requires);");
 }
 
 TEST_F(FormatTest, StatementAttributeLikeMacros) {
   FormatStyle Style = getLLVMStyle();
   StringRef Source = "void Foo::slot() {\n"
                      "  unsigned char MyChar = 'x';\n"
                      "  emit signal(MyChar);\n"
                      "  Q_EMIT signal(MyChar);\n"