This is exciting stuff!

My interpretation: If the JSIR project can successfully prove bi-directional source to MLIR transformation, it could lead to a new crop of source to source compilers across different languages (as long as they can be lowered to MLIR and back).

Imagine transmorphing Rust to Swift and back. Of course you’d still need to implement or shim any libraries used in the source language. This might help a little bit with C++ to Rust conversions - as more optimizations and analysis would now be possible at the MLIR level. Though I won’t expect unsafe code to magically become safe without some manual intervention.

For tsonic (https://github.com/tsoniclang/tsonic) which is trying to convert TS to C# and then to native binary via NativeAOT, I took almost the opposite tradeoff from JSIR.

JSIR is optimizing for round-trips back to JavaScript source. But since in language to language conversion teh consumer is a backend emitter (C# in my case), instead of preserving source structure perfectly, my IR preserves resolved semantic facts: types, generic substitutions, overload decisions, package/binding resolution, and other lowering-critical decisions.

I could be wrong, but I suspect transpilers are easier to build if it's lowering oriented (for specific targets).