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Add SPEEDTEST
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blyxyas committed Jun 10, 2023
1 parent d44ea7c commit 7a49175
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24 changes: 24 additions & 0 deletions book/src/development/speedtest.md
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# Speedtest
`SPEEDTEST` is the tool we use to measure lint's performance, it works by executing the same test several times.

It's useful for measuring changes to current lints and deciding if the performance changes too much. `SPEEDTEST` is
accessed by the `SPEEDTEST` (and `SPEEDTEST_*`) environment variables.

## Checking Speedtest

To do a simple speed test of a lint (e.g. `allow_attributes`), use this command.

```sh
$ SPEEDTEST=ui TESTNAME="allow_attributes" cargo uitest -- --nocapture
```

This will test all `ui` tests (`SPEEDTEST=ui`) whose names start with `allow_attributes`. By default, `SPEEDTEST` will
iterate your test 1000 times. But you can change this with `SPEEDTEST_ITERATIONS`.

```sh
$ SPEEDTEST=toml SPEEDTEST_ITERATIONS=100 TESTNAME="semicolon_block" cargo uitest -- --nocapture
```

> **WARNING**: Be sure to use `-- --nocapture` at the end of the command to see the average test time. If you don't
> use `-- --nocapture` (e.g. `SPEEDTEST=ui` `TESTNAME="let_underscore_untyped" cargo uitest -- --nocapture`), this
> will not show up.
40 changes: 36 additions & 4 deletions tests/compile-test.rs
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Expand Up @@ -355,10 +355,42 @@ fn run_ui_cargo() {
#[test]
fn compile_test() {
set_var("CLIPPY_DISABLE_DOCS_LINKS", "true");
run_ui();
run_ui_toml();
run_ui_cargo();
run_internal_tests();
// The SPEEDTEST_* env variables can be used to check Clippy's performance on your PR. It runs the
// affected test 1000 times and gets the average.
if let Ok(speedtest) = std::env::var("SPEEDTEST") {
println!("----------- STARTING SPEEDTEST -----------");
let f;
match speedtest.as_str() {
"ui" => f = run_ui as fn(),
"cargo" => f = run_ui_cargo as fn(),
"toml" => f = run_ui_toml as fn(),
"internal" => f = run_internal_tests as fn(),

_ => panic!("unknown speedtest: {speedtest} || accepted speedtests are: [ui, cargo, toml, internal]"),
}

let iterations;
if let Ok(iterations_str) = std::env::var("SPEEDTEST_ITERATIONS") {
iterations = iterations_str
.parse::<u64>()
.unwrap_or_else(|_| panic!("Couldn't parse `{}`, please use a valid u64", iterations_str));
} else {
iterations = 1000;
}

let mut sum = 0;
for _ in 0..iterations {
let start = std::time::Instant::now();
f();
sum += start.elapsed().as_millis();
}
println!("average {} time: {} millis.", speedtest.to_uppercase(), sum / 1000);
} else {
run_ui();
run_ui_toml();
run_ui_cargo();
run_internal_tests();
}
}

const RUSTFIX_COVERAGE_KNOWN_EXCEPTIONS: &[&str] = &[
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