## Summary
A new CLI option (`-o`/`--output-file`) to write output to a file
instead of stdout.
Major change is to remove the lock acquired on stdout. The argument is
that the output is buffered and thus the lock is acquired only when
writing a block (8kb). As per the benchmark below there is a slight
performance penalty.
Reference:
https://rustmagazine.org/issue-3/javascript-compiler/#printing-is-slow
## Benchmarks
_Output is truncated to only contain useful information:_
Command: `check --isolated --no-cache --select=ALL --show-source
./test-repos/cpython"`
Latest HEAD (361d45f2b2) with and without
the manual lock on stdout:
```console
Benchmark 1: With lock
Time (mean ± σ): 5.687 s ± 0.075 s [User: 17.110 s, System: 0.486 s]
Range (min … max): 5.615 s … 5.860 s 10 runs
Benchmark 2: Without lock
Time (mean ± σ): 5.719 s ± 0.064 s [User: 17.095 s, System: 0.491 s]
Range (min … max): 5.640 s … 5.865 s 10 runs
Summary
(1) ran 1.01 ± 0.02 times faster than (2)
```
This PR:
```console
Benchmark 1: This PR
Time (mean ± σ): 5.855 s ± 0.058 s [User: 17.197 s, System: 0.491 s]
Range (min … max): 5.786 s … 5.987 s 10 runs
Benchmark 2: Latest HEAD with lock
Time (mean ± σ): 5.645 s ± 0.033 s [User: 16.922 s, System: 0.495 s]
Range (min … max): 5.600 s … 5.712 s 10 runs
Summary
(2) ran 1.04 ± 0.01 times faster than (1)
```
## Test Plan
Run all of the commands which gives output with and without the
`--output-file=ruff.out` option:
* `--show-settings`
* `--show-files`
* `--show-fixes`
* `--diff`
* `--select=ALL`
* `--select=All --show-source`
* `--watch` (only stdout allowed)
resolves: #4754
## Summary
This adds `json-lines` (https://jsonlines.org/ or http://ndjson.org/) as
an output format.
I'm sure you already know, but
* JSONL is more greppable (each record is a single line) than the pretty
JSON
* JSONL is faster to ingest piecewise (and/or in parallel) than JSON
## Test Plan
Snapshot test in the new module :)
