[clang] [Clang][Lex] Fix parsing of nested requirement to prevent flowing off the end of token stream (PR #73691)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik updated https://github.com/llvm/llvm-project/pull/73691

>From 21d6bbdd1f8676e51b053ec3dd9020270e6b929e Mon Sep 17 00:00:00 2001
From: Shafik Yaghmour <shafik.yaghmour at intel.com>
Date: Tue, 28 Nov 2023 11:20:12 -0800
Subject: [PATCH] [Clang][Lex] Fix parsing of nested requirement to prevent
 flowing off the end of token stream

Currently when parsing a nested requirement we attempt to balance parens if we
have a parameter list. This will fail in some cases of ill-formed code and keep
going until we fall off the token stream and crash. This fixes the hand parsing
by using SkipUntil which will properly flag if we don't find the expected
tokens.

Fixes: https://github.com/llvm/llvm-project/issues/73112
---
 clang/docs/ReleaseNotes.rst                        | 3 +++
 clang/lib/Parse/ParseExprCXX.cpp                   | 6 ++++--
 clang/test/Parser/cxx2a-concepts-requires-expr.cpp | 8 ++++++++
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7c909ac3cab6419..f8abc44743da09c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/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.
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 79db094e098f8e6..8b86db1bb8fc5d5 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/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))
diff --git a/clang/test/Parser/cxx2a-concepts-requires-expr.cpp b/clang/test/Parser/cxx2a-concepts-requires-expr.cpp
index a18a54c7fad0690..971591afb08dba2 100644
--- a/clang/test/Parser/cxx2a-concepts-requires-expr.cpp
+++ b/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 '('}}
+}
+}