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fix(es/minifier): keep directive prologue when merging if returns (#12580)
The `if_return` pass merged the directive prologue of a function body
into a sequence expression. A directive such as `"use strict"` then
became a discarded `void` operand and stopped being a directive. The
function lost strict mode. For example, `this` in a strict function
became the global object, and `arguments` aliased its parameters.
This change keeps the leading string-literal statements of a function
body out of the `if_return` merge. The pass still merges the statements
after them. This applies to ordinary functions and to block-bodied arrow
functions.
Tests:
- Add the fixtures `issues/9238`, `issues/9238-arrow` and
`issues/9238-prologue`. They check `arguments` aliasing, `this` in a
strict function, a returned function in a strict arrow, multiple
directives, and safe merging of ordinary statements. Each fixture also
has a `expected.repeat-stdout` check for two minification rounds. All
new fixtures fail without the fix.
- Update the `next/swc-4559` snapshot. It now keeps `"use strict"`,
which the old output wrongly dropped.
- Update the antd gzipped size in `libs-size.snapshot.md` (+0.01 KiB)
for the same reason.
Local validation (on the final revision): `cargo fmt --all`, `cargo
clippy --all --all-targets -- -D warnings`, `cargo test -p
swc_ecma_minifier` and `crates/swc_ecma_minifier/scripts/exec.sh`
passed. CI was not run locally.
Closes #9238
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Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com> Latest Branches
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