This isn't the first time there has been a proposal for a "safe" C++ while at the end of November Chuanqi Xu announced this newest initiative to come up with a "Safe C++" based on the ClangIR intermediate representation that would come down to being a pure subset of ISO C++ with a few ignorable pragma and attributes. The simpler approach would allow compiling the subset by other C++ compilers not supporting this "safe" dialect.
ClangIR is the new intermediate representation (IR) that has been brewing as an MLIR dialect for C?C++ languages that is described in the documentation as being between Clang's AST and LLVM IR. ClangIR can handle C/C++ higher level semantics for better diagnostics and performance optimizations that are harder to achieve in pure Clang AST or LLVM IR. Those wanting to learn more about the in-development ClangIR can do so via the documentation for that in-progress effort.
Chuanqi Xu is looking to leverage ClangIR to produce a safer C++ and has already produced a demo implementation. Among the proposal is adding a pragma "#pragma clang SafeCXX" for defining the same C++ code that other compilers can ignore if unsupported. Similarly there would be a "#pragma clang UnsafeCXX" too for sections of unsafe C++ code.
The thinking is with the ClangIR-based Safe C++ to provide borrow checking, different handling for deprecated calls, deprecating the user of pointers / taking addresses / dereferencing, references within async functions, and other changes to make C++ code safer by better leveraging modern compiler technologies within LLVM/Clang.
The proposal is a bit premature with ClangIR itself not yet being stabilized but those interested can see the RFC proposal on the LLVM Discourse . Some of the early prototyped code can be found via this GitHub repository . It will be interesting to see what comes of this safe C++ effort and more broadly the ClangIR development in 2025.