elixir-gettext / gettext / 888917e1e9e6af5b0f6c79bf7e502ab5532278ef-PR-436

93%

main: 93%

Pull #436

github

Parallelize locale merging in mix gettext.merge

mix gettext.merge processes locales sequentially, but each locale's
merge is fully independent: every locale task writes only to its own
<pot_dir>/<locale>/LC_MESSAGES/*.po files, the POT files at the root of
pot_dir are only read, and Gettext.Merger is stateless (pure functions
over Expo structs). Switch merge_all_locale_dirs/3 to Task.async_stream
over locales, mirroring the existing Task.async_stream over POT files
within a locale in merge_dirs/5.

The return value change (list -> :ok via Stream.run/1) is safe: the
only caller is merge_messages_dir/3, whose result is discarded in
run/1. The --locale single-locale path is untouched. A crashed locale
task raises out of Stream.run/1, matching the sequential version's
failure behavior. Mix.shell() output is GenServer-backed, so concurrent
lines serialize correctly; the only observable change is that progress
lines from different locales can interleave, as already happens in
Gettext.Compiler's parallel paths.

Benchmark on a 16-locale / 11-domain Phoenix app (160 PO files, ~4,700
msgids, Elixir 1.20.1 / OTP 29, Apple Silicon):

    mix gettext.merge priv/gettext --no-fuzzy

    before: 9.4s wall (55% CPU)
    after:  1.9-2.4s wall (341-381% CPU)

~4.9x speedup with byte-identical output files (clean git status over
committed PO state after both runs). The win scales with locale count.

3 of 3 new or added lines in 1 file covered. (100.0%)

647 of 698 relevant lines covered (92.69%)

26.7 hits per line