You speak of Bublé as though it goes unused. It still gets plenty of use, not least because of how much faster it is than Babel, but also because of its focus on cheapness of its transformations at runtime—Babel focuses on being as close to correct as possible, but at quite a substantial runtime cost in code size and speed. (I understand Babel also has loose transformations, https://babeljs.io/docs/en/babel-preset-env#loose, that are like Bublé’s, but I have never compared the two; they definitely feel like they’re a second-class citizen in Babel.) The less-different code is also great for when you inevitably need to read the generated code without source maps, too, since it is made up of simple AST-guided source transformations rather than total rewrites of features.
In all, I much prefer Bublé to Babel for code I control, although sometimes I would like the extra transformations that you can do with Babel.
For my priorities, I would genuinely see switching to swc as a functional regression if it does not support such loose transformations.
I’d be interested to see a hybrid approach that focused on loose transformations and used the faster AST-guided source transformation approach where feasible, and localised full AST rewrites where not feasible. In JavaScript the performance difference between a full AST rewrite (Babel) and AST-guided source transformation (Bublé) is stark; my feeling is that it will be less distinct, but still substantial, in Rust.
In all, I much prefer Bublé to Babel for code I control, although sometimes I would like the extra transformations that you can do with Babel.
For my priorities, I would genuinely see switching to swc as a functional regression if it does not support such loose transformations.
I’d be interested to see a hybrid approach that focused on loose transformations and used the faster AST-guided source transformation approach where feasible, and localised full AST rewrites where not feasible. In JavaScript the performance difference between a full AST rewrite (Babel) and AST-guided source transformation (Bublé) is stark; my feeling is that it will be less distinct, but still substantial, in Rust.