Mid stack inlining in Go: https://go.googlesource.com/proposal/+/master/design/19348-midstack-inlining.md
(Interesting implementation details: the inliner is AST based, how to preserve existing stack reflection APIs, and how to show good tracebacks.)
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Co-Authored-By: An old Stack Overflow answer, blindly accepting the compiler's suggestions, and a linter.
I think you could build an interesting IDE with a tiny embedded LLM in addition to the usual tooling.
Features like 'extract method' would be much nicer if an LLM could provide a name. Choosing a good name is virtually impossible from just a typed AST.
What are the most popular languages that have used an AST walker for their implementation?
I know Ruby used to do this, but there must be others.
(I'm interested in the lowest PL speed that users will tolerate if you have awesome features.)