Add Sept 2024 issue of This Month in Our Test Infra post (#1414)

posts/inside-rust/2024-10-10-test-infra-oct-2024.md

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+---
+layout: post
+title: "This Month in Our Test Infra: September 2024"
+author: Jieyou Xu
+team: the Bootstrap Team <https://www.rust-lang.org/governance/teams/infra#team-bootstrap>
+---
+
+# This Month in Our Test Infra: September 2024
+
+This is a quick summary of the changes in the test infrastructure for the
+[rust-lang/rust][rust] repository[^scope] for September 2024. It also includes
+brief descriptions of on-going work.
+
+[^scope]: The test infra here refers to the test harness [compiletest] and
+supporting components in our build system [bootstrap]. This test infra is used
+mainly by rustc and rustdoc. Other tools like cargo, miri or rustfmt maintain
+their own test infra.
+
+As usual, if you encounter bugs or UX issues when using our test infrastrucutre,
+please [file an issue][new-issue]. Bugs and papercuts can't be fixed if we don't
+know about them!
+
+## Changes
+
+### `run-make` test suite now has access to a properly-staged cargo
+
+[bootstrap] now builds a properly-staged cargo and makes it available for
+`run-make` tests. Previously, `run-make` tests just used whatever initial cargo
+[bootstrap] had access to, but this caused problems if a `run-make` test uses a
+cargo feature that's present in nightly but not in beta. We encountered some
+interesting build cache invalidation issues related to differing `RUSTFLAGS` in
+the process, but were able to fix them. We want to add mechanisms to [bootstrap]
+to make it harder to misuse `RUSTFLAGS` which may lead to hard-to-diagnose build
+cache invalidation in the future.
+
+- bootstrap: [Fix cargo staging for run-make tests #130739](https://github.com/rust-lang/rust/pull/130739)
+- bootstrap/compiletest: [Pass the current cargo to run-make tests #130642](https://github.com/rust-lang/rust/pull/130642)
+- bootstrap: [Prevent building cargo from invalidating build cache of other
+  tools due to conditionally applied `-Zon-broken-pipe=kill` via tracked
+  `RUSTFLAGS` #131155](https://github.com/rust-lang/rust/pull/131155)
+
+Why `-Zon-broken-pipe=kill` is required when building rustc was its [own entire
+rabbit hole](https://github.com/rust-lang/rust/issues/131436), in case you were
+curious.
+
+### More `run-make` migrations and fixes
+
+The `emit-to-stdout` `run-make` test was ported to `rmake.rs`, only [10 more to
+go]. The remaining ones are stuck on being quite tricky. See the [tracking
+issue][port-run-make] for why we are transitioning away from `Makefile`s in
+`run-make` tests.
+
+- run-make: [port `emit-to-stdout` to rmake.rs #131355](https://github.com/rust-lang/rust/pull/131355)
+
+Misc:
+
+- run-make: [Add missing `needs-llvm-components` directives for run-make tests
+  that need target-specific codegen
+  #129605](https://github.com/rust-lang/rust/pull/129605)
+
+[remaining-run-make-tests]: https://github.com/rust-lang/rust/blob/883f9a2c8f8923eafafbeba8b18361424b148f05/src/tools/tidy/src/allowed_run_make_makefiles.txt#L1C1-L10C30
+[port-run-make]: https://github.com/rust-lang/rust/issues/121876
+
+### `run_make_support` library updates
+
+`run_make_support` is the support library built and made available to `run-make`
+tests.
+
+- run_make_support: [Add `llvm-pdbutil` wrapper #130048](https://github.com/rust-lang/rust/pull/130048)
+- run_make_support: [Rename `Command::stdin` to `stdin_buf` and add
+  `std{in,out,err}` config helpers
+  #129973](https://github.com/rust-lang/rust/pull/129973)
+- run_make_support: [Rectify symlink handling
+  #130427](https://github.com/rust-lang/rust/pull/130427)
+
+### [compiletest] improvements and fixes
+
+We dropped [compiletest]'s legacy directive check (e.g. `// ignore-test hello`
+no longer warns). This was originally added when we migrated from `//` to `//@`
+to help test writers notice the new directives, but now a long time has passed
+so we can remove it as it was causing friction in adding new directives and
+authoring tests. For example, the [Specification Team][t-spec] wanted to add a
+`//@ reference` directive, but the legacy directive check would trigger on:
+
+```rust,no_run
+// So what if we added a
+// reference to the           <- `reference` is a known directive, and
+//                               `// reference` looks suspcious!
+// rustc-dev-guide?
+```
+
+This was added to initially to help migration from `//` to `//@`, but since a
+long time has passed we no longer need this check to help contributors know that
+legacy directives are being phased out.
+
+- compiletest: [Drop compiletest legacy directive check
+  #131392](https://github.com/rust-lang/rust/pull/131392)
+
+[t-spec]: https://www.rust-lang.org/governance/teams/lang#team-spec
+
+We updated some `compiletest` normalizations and directive renaming. In
+particular, we restricted `//@ ignore-mode-*` directives to not accept *all*
+test suites, and later converted `//@ ignore-mode-coverage-map` and `//@
+ignore-mode-coverage-run` to `//@ ignore-coverage-map` and `//@
+ignore-coverage-run` because only `coverage-map` and `coverage-run` were special
+in that the same test source files ran under two test suite configurations.
+
+- compiletest: [Add `{{rust-src-base}}` (for sysroot src base)
+  #129687](https://github.com/rust-lang/rust/pull/129687)
+- compiletest: [Restrict `ignore-mode-*` directives
+  #131346](https://github.com/rust-lang/rust/pull/131346)
+- compiletest: [Simplify the compiletest directives for ignoring coverage-test
+  modes #131400](https://github.com/rust-lang/rust/pull/131400)
+
+We broke up [compiletest]'s `runtest.rs` as it was [previously
+*massive*][prev-runtest], clocking in at 4710 lines. It's now around 2700 lines,
+so still massive, but at least slightly less so.
+
+- compiletest: [Break up compiletest `runtest.rs` into smaller helper modules
+  #130566](https://github.com/rust-lang/rust/pull/130566)
+
+[prev-runtest]: https://github.com/rust-lang/rust/blob/b7b9453ea7354ee39b15390ffd0b4f9e2000076b/src/tools/compiletest/src/runtest.rs
+
+We added a help message upon `crashes` test failure that you can set
+`COMPILETEST_VERBOSE_CRASHES=1` to get compiler stderr/stdout output from trying
+to build the failing `crashes` test.
+
+- compiletest: [Mention `COMPILETEST_VERBOSE_CRASHES` on crashes test failure
+  #130793](https://github.com/rust-lang/rust/pull/130793)
+
+We also registered [tool docs][compiletest-tool-docs] for [compiletest]. There
+currently isn't much doc comments in [compiletest], but having them getting
+built and made available as part of nightly rustc docs is a good first step.
+
+- bootstrap: [Register tool docs for compiletest
+  #130567](https://github.com/rust-lang/rust/pull/130567)
+
+[compiletest-tool-docs]: https://doc.rust-lang.org/nightly/nightly-rustc/compiletest/index.html
+
+Misc:
+
+- compiletest: [Rename "runtest/crash.rs" to "runtest/crashes.rs" to be in line
+  with the test directory
+  #130973](https://github.com/rust-lang/rust/pull/130973)
+
+### Testing documentation improvements
+
+We improved testing docs in [rustc-dev-guide][dev-guide-testing]. We added a
+[testing best practices chapter][dev-guide-testing-best-practices], and updated
+the [compiletest directives listing][dev-guide-directives-listing].
+
+- rustc-dev-guide: [Revise testing chapters excluding the directives chapter
+  #2088](https://github.com/rust-lang/rustc-dev-guide/pull/2088)
+- rustc-dev-guide: [Revise directives docs
+  #2089](https://github.com/rust-lang/rustc-dev-guide/pull/2089)
+- rustc-dev-guide: [Revise test naming advice to discourage using issue numbers
+  alone #2090](https://github.com/rust-lang/rustc-dev-guide/pull/2090)
+- rustc-dev-guide: [Document compiletest directives `ignore-coverage-map` and
+  `ignore-coverage-run`
+  #2094](https://github.com/rust-lang/rustc-dev-guide/pull/2094)
+- rustc-dev-guide: [Small follow-up to my "internal #[rustc_*] TEST attributes"
+  PR #2082](https://github.com/rust-lang/rustc-dev-guide/pull/2082)
+- rustc-dev-guide: [Note lldb debuginfo requires `python310.dll` to be present
+  in `PATH` on Windows
+  #2076](https://github.com/rust-lang/rustc-dev-guide/pull/2076)
+- rustc-dev-guide: [Document crashes test suite
+  #2075](https://github.com/rust-lang/rustc-dev-guide/pull/2075)
+- rustc-dev-guide: [Purge `run-pass-valgrind mentions`
+  #2091](https://github.com/rust-lang/rustc-dev-guide/pull/2091)
+- rustc-dev-guide: [Add documentation for `{{rust-src-base}}`
+  #2079](https://github.com/rust-lang/rustc-dev-guide/pull/2079)
+
+There's still a lot of room for improvement in our testing docs -- in
+[compiletest], [bootstrap] and [rustc-dev-guide], but one step at a time.
+
+[dev-guide-testing]: https://rustc-dev-guide.rust-lang.org/tests/intro.html
+[dev-guide-testing-best-practices]: https://rustc-dev-guide.rust-lang.org/tests/best-practices.html
+[dev-guide-directives-listing]: https://rustc-dev-guide.rust-lang.org/tests/directives.html
+
+### Test suite cleanups
+
+We deleted an entire test suite `run-pass-valgrind` because it was never
+properly wired up and properly implemented, and was not used. It turns out
+deleting the test suite actually fixes a bug from 2017 [run-pass-valgrind tests
+don't actually run in valgrind
+#44816](https://github.com/rust-lang/rust/issues/44816) because you can't have a
+test suite related bug if the test suite doesn't exist!
+
+- bootstrap/compiletest/opt-dist: [Remove valgrind test suite and support from
+  compiletest, bootstrap and opt-dist
+  #131351](https://github.com/rust-lang/rust/pull/131351)
+
+Misc:
+
+- rustdoc: [Rename `issue-\d+.rs` tests to have meaningful names (part 9)
+  #130287](https://github.com/rust-lang/rust/pull/130287)
+
+## On-going developments
+
+- Add test infrastructure support for a `minicore` test auxiliary, so that
+  `#![no_std]` cross-compiling build-only tests don't need to reinvent and
+  reimplement `core` prelude stubs again and again. See
+  <https://github.com/rust-lang/rust/issues/131485>.
+- We want to make `RUSTFLAGS` harder to misuse that can lead to tool build cache
+  invalidation, leading to unnecessary rebuilds.
+- There's on-going effort to redesign stage0 std, to help make [bootstrap]
+  staging more consistent and more intuitive.
+
+[rust]: https://github.com/rust-lang/rust
+[compiletest]: https://github.com/rust-lang/rust/tree/master/src/tools/compiletest
+[bootstrap]: https://github.com/rust-lang/rust/tree/master/src/bootstrap
+[new-issue]: https://github.com/rust-lang/rust/issues/new
+[rustc-dev-guide]: https://rustc-dev-guide.rust-lang.org/getting-started.html