[clang] [C++26] [Contracts] Support Parser, AST and AST Serialization (1/n) (PR #205739)

[Yihan Wang via cfe-commits]

================
@@ -158,6 +158,12 @@ StmtResult Parser::ParseStatementOrDeclarationAfterAttributes(
         getCurScope(), SemaCodeCompletion::PCC_Statement);
     return StmtError();
 
+  // C++26 contract_assert statement (P2900R14).
+  case tok::kw_contract_assert:
----------------
yronglin wrote:

Should we diagnose if we see `kw_contract_assert` but constracts disabled?

https://github.com/llvm/llvm-project/pull/205739