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Mention RUSTC_BOOTSTRAP for misc testing (rust-lang#2136)
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jieyouxu authored Nov 18, 2024
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1 change: 1 addition & 0 deletions src/SUMMARY.md
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- [Rust for Linux](./tests/rust-for-linux.md)
- [Performance testing](./tests/perf.md)
- [Suggest tests tool](./tests/suggest-tests.md)
- [Misc info](./tests/misc.md)
- [Debugging the compiler](./compiler-debugging.md)
- [Using the tracing/logging instrumentation](./tracing.md)
- [Profiling the compiler](./profiling.md)
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4 changes: 4 additions & 0 deletions src/tests/intro.md
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A separate infrastructure is used for testing and tracking performance of the
compiler. See the [Performance testing chapter](perf.md) for more details.

## Miscellaneous information

There are some other useful testing-related info at [Misc info](misc.md).

## Further reading

The following blog posts may also be of interest:
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40 changes: 40 additions & 0 deletions src/tests/misc.md
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# Miscellaneous testing-related info

## `RUSTC_BOOTSTRAP` and stability

<!-- date-check: Nov 2024 -->

This is a bootstrap/compiler implementation detail, but it can also be useful
for testing:

- `RUSTC_BOOTSTRAP=1` will "cheat" and bypass usual stability checking, allowing
you to use unstable features and cli flags on a stable `rustc`.
- `RUSTC_BOOTSTRAP=-1` will force a given `rustc` to pretend that is a stable
compiler, even if it's actually a nightly `rustc`. This is useful because some
behaviors of the compiler (e.g. diagnostics) can differ depending on whether
the compiler is nightly or not.

In `ui` tests and other test suites that support `//@ rustc-env`, you can specify

```rust,ignore
// Force unstable features to be usable on stable rustc
//@ rustc-env:RUSTC_BOOTSTRAP=1
// Or force nightly rustc to pretend it is a stable rustc
//@ rustc-env:RUSTC_BOOTSTRAP=-1
```

For `run-make` tests, `//@ rustc-env` is not supported. You can do something
like the following for individual `rustc` invocations.

```rust,ignore
use run_make_support::rustc;
fn main() {
rustc()
// Pretend that I am very stable
.env("RUSTC_BOOTSTRAP", "-1")
//...
.run();
}
```

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