minimally implement `is` (RFC 3573), sans parsing - #144174

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dianne wants to merge 3 commits into

rust-lang:mainfrom

dianne:desugar-is

Commits on Jul 24, 2025

add `ast::ExprKind::Is` and placeholder builtin syntax
dianne
committed
046d89b
desugar `is` outside of `if`/`while` conditions
dianne
committed
d9cfd3e

Commits on Jul 25, 2025

additional tests for `is` expressions' lexical scope

dianne
and
joshtriplett
committed
92fd27c