[Clang][Lex] Fix parsing of nested requirement to prevent flowing off the end of token stream

clang/docs/ReleaseNotes.rst

@@ -783,6 +783,9 @@ Bug Fixes to C++ Support
   completes (except deduction guides). Fixes:
   (`#59827 <https://github.com/llvm/llvm-project/issues/59827>`_)
 
+- Fix crash when parsing nested requirement. Fixes:
+  (`#73112 <https://github.com/llvm/llvm-project/issues/73112>`_)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.

clang/lib/Parse/ParseExprCXX.cpp

@@ -3635,10 +3635,12 @@ ExprResult Parser::ParseRequiresExpression() {
               auto Res = TryParseParameterDeclarationClause();
               if (Res != TPResult::False) {
                 // Skip to the closing parenthesis
-                // FIXME: Don't traverse these tokens twice (here and in
-                //  TryParseParameterDeclarationClause).
                 unsigned Depth = 1;
                 while (Depth != 0) {
+                  bool FoundParen = SkipUntil(tok::l_paren, tok::r_paren,
+                                              SkipUntilFlags::StopBeforeMatch);
+                  if (!FoundParen)
+                    break;
                   if (Tok.is(tok::l_paren))
                     Depth++;
                   else if (Tok.is(tok::r_paren))

clang/test/Parser/cxx2a-concepts-requires-expr.cpp

@@ -160,3 +160,11 @@ template <int N>
 requires requires {
  typename BitInt<N>; // ok
 } using r44 = void;
+
+namespace GH73112 {
+void f() {
+    requires { requires(int; } // expected-error {{expected ')'}} \
+                               // expected-error {{expected expression}} \
+                               // expected-note {{to match this '('}}
+}
+}