Add Dec 2024 issue of This Month In Our Test Infra

Author: jieyouxu

posts/inside-rust/2025-01-10-test-infra-dec-2024.md

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+---
+layout: post
+title: "This Month in Our Test Infra: December 2024"
+author: Jieyou Xu
+team: the Bootstrap Team <https://www.rust-lang.org/governance/teams/infra#team-bootstrap>
+---
+
+# This Month in Our Test Infra: December 2024
+
+<!-- time period: 2024-12-04 through 2025-01-05 -->
+
+Happy new year, dear reader! This is the last *This Month in Our Test Infra* issue for 2024.
+
+This is a quick summary of the changes in the test infrastructure for the [rust-lang/rust] repository[^scope] for **December 2024**.
+
+[^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 infrastructure, please [file an issue][new-issue]. Bugs and papercuts can't be fixed if we don't know about them!
+
+**Thanks to everyone who contributed to our test infra!**
+
+## Highlights
+
+### `rustc-dev-guide` is now a `josh` subtree!
+
+Previously, [rustc-dev-guide] was a submodule inside [rust-lang/rust], and updates to [rustc-dev-guide] had to be done in a separate PR against the [rustc-dev-guide] repository.
+
+Now, thanks to [@Kobzol](https://github.com/Kobzol)'s efforts (which included overcoming many unforeseen obstacles), [`rustc-dev-guide` is now a `josh` subtree][pr-134907]. This is a significant improvement for contribution workflows because it means that documentation updates to [rustc-dev-guide] can accompany the implementation change in [rust-lang/rust] in the same PR. The reduction in contribution friction also encourages [rustc-dev-guide] updates because you no longer have to author and maintain two separate PRs.
+
+[pr-134907]: https://github.com/rust-lang/rust/pull/134907
+
+### compiletest will now show the difference between normalized output and actual output for differing lines
+
+Previously, it can be very difficult to tell when a ui test fails what the actual output is pre-normalization, as you would have to resort to `--nocapture` or similar.
+
+Now, [compiletest will also show the pre-normalization mismatched output lines on failure to make this easier to tell][pr-133733]. Example output:
+
+```text
+failures:
+
+---- [ui] tests/ui/layout/enum.rs stdout ----
+diff of stderr:
+
+-	error: align: AbiAndPrefAlign { abi: Align(2 bytes), pref: $PREF_ALIGN }
++	error: align: AbiAndPrefAlign { abi: Align(2 bytes), pref: $PREF_ALIN }
+2	  --> $DIR/enum.rs:9:1
+3	   |
+4	LL | enum UninhabitedVariantAlign {
+
+Note: some mismatched output was normalized before being compared
+-	error: align: AbiAndPrefAlign { abi: Align(2 bytes), pref: Align(8 bytes) }
+-	  --> /home/jyn/src/rust2/tests/ui/layout/enum.rs:9:1
++	error: align: AbiAndPrefAlign { abi: Align(2 bytes), pref: $PREF_ALIN }
+```
+
+[pr-133733]: https://github.com/rust-lang/rust/pull/133733
+
+### compiletest now allows using a specific debugger when running debuginfo tests
+
+For a long time, the `tests/debuginfo` test suite could only be successfully run if you had all the tested debuggers (being `lldb`, `gdb`, `cdb`). This is very annoying locally if:
+
+- One or more of these debuggers are not available or don't work locally[^lldb].
+- You just wanted to look at the test failures for a given debugger.
+
+Now, you are able to run the `tests/debuginfo` test suite with a *specific* debugger, to only run the tests against that specified debugger. Example usage:
+
+```bash
+$ ./x test tests/debuginfo -- --debugger gdb
+```
+
+### `ui` tests now support `//@ forbid-output`
+
+`ui` tests can now use the `//@ forbid-output: REGEX` directive to check for a pattern which must not appear in the stderr. If the `REGEX` pattern is matched, then the `ui` test will fail.
+
+Please consult [rustc-dev-guide] for more details.
+
+### `./x test` now accepts a `--no-capture` flag which will be forwarded to compiletest (and thus libtest)
+
+Previously, if you wanted to pass the `--nocapture` flag through [bootstrap], through [compiletest], to the underlying [libtest] runner, on Linux you have to write:
+
+```bash
+$ ./x test tests/ui -- --nocapture
+```
+
+On native Windows msvc it's even worse, I recall having to write
+
+```powershell
+PS> ./x test tests/ui -- -- --nocapture
+```
+
+Which is hard to discover and a contributor papercut[^nocapture].
+
+Now, you can just write
+
+```bash
+$ ./x test tests/ui --no-capture
+```
+
+and bootstrap will forward this flag as `--nocapture` to the underlying [libtest].
+
+
+## Notable changes
+
+This section is intended to be like a "compatibility notes" but for human test writers.
+
+### `FileCheck`-based test suites no longer predefine `MSVC` and `NONMSVC` `FileCheck` prefixes
+
+In the *current* setup, compiletest will register a [`FileCheck`][filecheck] custom prefix for each compiletest `//@ revision`. However, for historical reasons compiletest also predefined `MSVC` and `NONMSVC` `FileCheck` prefixes depending on the *host*. But this is very surprising for two reasons:
+
+1. It's "spooky action in a distance" because the user never declared these custom prefixes, and these prefixes are conditionally set based on the host. It's hard to debug too.
+2. If the user also wants to add their own `//@ revision: MSVC NONMSVC` revisions, because compiletest would pass `--check-prefix` for those names twice, this will cause `FileCheck` to report an error about duplicate prefixes.
+
+Therefore, in [compiletest: don't register predefined `MSVC`/`NONMSVC` `FileCheck` prefixes #134463](https://github.com/rust-lang/rust/pull/134463) we no longer predefine these two `FileCheck` prefixes.
+
+If you want the previous `MSVC` vs `NONMSVC` behavior, you will need to explicitly write out
+
+```rs
+//@ revisions: MSVC NONMSVC
+//@[MSVC] only-windows-msvc
+//@[NONMSVC] ignore-windows-msvc
+```
+
+### `normalize-{stderr,stdout}-test` directives are renamed to `normalize-{stderr,stdout}`
+
+Mostly a cleanup, the `-test` suffixes provide no additionally useful information, and only make these two `normalize-*` directives hard to discover.
+
+`normalize-{stderr,stdout}-test` directives are now [renamed to `normalize-{stderr,stdout}`][pr-134759]. `normalize-{stderr,stdout}-{32,64}bit` directives remain unaffected.
+
+[pr-134759]: https://github.com/rust-lang/rust/pull/134759
+
+### compiletest will now deny usages of builtin `FileCheck` suffixes as revision names (for `FileCheck`-based test suites)
+
+For [`FileCheck`][filecheck]-based test suites (`assembly`, `codegen`, `mir-opt`), compiletest will register a custom `FileCheck` prefix for each compiletest `//@ revision`. However, `FileCheck` also has some [builtin suffixes][filecheck-suffixes] such as:
+
+```rust
+// COM:
+// CHECK:
+// CHECK-NEXT:
+// CHECK-SAME:
+// CHECK-EMPTY:
+// CHECK-NOT:
+// CHECK-COUNT:
+// CHECK-DAG:
+// CHECK-LABEL:
+```
+
+When combined, this previously meant that the compiletest revision + builtin `FileCheck` suffix constructions such as
+
+```rust
+// next:
+// same-SAME:
+// not-NOT:
+// next-NEXT:
+// not-SAME:
+```
+
+are permitted by compiletest, which are incredibly confusing.
+
+As such, compiletest will now reject `CHECK`, `COM`, `NEXT`, `SAME`, `EMPTY`, `NOT`, `COUNT`, `DAG`, `LABEL` as revision names in `FileCheck`-based test suites.
+
+[filecheck-suffixes]: https://llvm.org/docs/CommandGuide/FileCheck.html#the-check-next-directive
+
+
+## PR listing
+
+### Improvements
+
+- [rustc-dev-guide]: [Turn `rustc-dev-guide` into a `josh` subtree #134907](https://github.com/rust-lang/rust/pull/134907)
+- [compiletest]: [Show the difference between the normalized output and the actual output for lines which didn't match #133733](https://github.com/rust-lang/rust/pull/133733)
+- [compiletest]: [Explain that UI tests are expected not to compile by default #133813](https://github.com/rust-lang/rust/pull/133813)
+- [compiletest]: [Allow using a specific debugger when running `debuginfo` tests #134629](https://github.com/rust-lang/rust/pull/134629)
+- [compiletest], [run-make-support]: [Improve `compiletest` and `run-make-support` symlink handling](https://github.com/rust-lang/rust/pull/134659)
+- [compiletest]: [Support `forbid-output` in UI tests #134738](https://github.com/rust-lang/rust/pull/134738)
+- [bootstrap]: [Add `--no-capture`/`--nocapture` as bootstrap arguments #134809](https://github.com/rust-lang/rust/pull/134809)
+- [bootstrap]: [Allow `./x check compiletest` #134848](https://github.com/rust-lang/rust/pull/134848)
+- [compiletest]: [Deny usage of special `FileCheck` suffixes as revision names #134925](https://github.com/rust-lang/rust/pull/134925)
+- [tidy]: [Run Python formatting check in `tidy` on CI #134964](https://github.com/rust-lang/rust/pull/134964)
+- [tidy]: [Print how to rebless Python formatting in `tidy` #134968](https://github.com/rust-lang/rust/pull/134968)
+
+### Fixes
+
+- [compiletest]: [Fix `--nocapture` for `run-make` tests #134111](https://github.com/rust-lang/rust/pull/134111)
+- [compiletest]: [Remove empty 'expected' files when blessing #134808](https://github.com/rust-lang/rust/pull/134808)
+- [run-make]: [Fix `assert_stderr_not_contains_regex` #134113](https://github.com/rust-lang/rust/pull/134113)[^oops]
+
+### Cleanups
+
+- [compiletest]: [Don't register predefined `MSVC`/`NONMSVC` `FileCheck` prefixes](https://github.com/rust-lang/rust/pull/134463)
+- [compiletest]: [Remove the `-test` suffix from `normalize-*` directives #134759](https://github.com/rust-lang/rust/pull/134759)
+- [compiletest]: [Only pass the post-colon value to `parse_normalize_rule` #134840](https://github.com/rust-lang/rust/pull/134840)
+- [compiletest]: [Slightly simplify the handling of debugger directive prefixes #134849](https://github.com/rust-lang/rust/pull/134849)
+- [bootstrap]: [Consolidate the macros for declaring compiletest test suites #134876](https://github.com/rust-lang/rust/pull/134876)
+- [tidy]: [Replace `black` with `ruff` in `tidy` #133821](https://github.com/rust-lang/rust/pull/133821)
+
+### Documentation updates
+
+- [Document how to run the split Docker pipelines #134894](https://github.com/rust-lang/rust/pull/134894)
+- [Document the `--dev` flag for `src/ci/docker/run.sh` #134669](https://github.com/rust-lang/rust/pull/134669)
+- [rustc-dev-guide]: [`compiletest`: Document the `--debugger` flag #2170](https://github.com/rust-lang/rustc-dev-guide/pull/2170)
+- [rustc-dev-guide]: [Document `forbid-output` for UI tests #2171](https://github.com/rust-lang/rustc-dev-guide/pull/2171)
+- [rustc-dev-guide]: [Remove the `-test` suffix from normalize directives #2172](https://github.com/rust-lang/rustc-dev-guide/pull/2172)
+- [rustc-dev-guide]: [Document `x test --no-capture` #2174](https://github.com/rust-lang/rustc-dev-guide/pull/2174)
+- [rustc-dev-guide]: [Describe how to use rust-analyzer with `rmake.rs` #2191](https://github.com/rust-lang/rustc-dev-guide/pull/2191)
+
+
+[rust-lang/rust]: https://github.com/rust-lang/rust
+[rustc-dev-guide]: https://github.com/rust-lang/rustc-dev-guide
+[compiletest]: https://github.com/rust-lang/rust/tree/master/src/tools/compiletest
+[run-make-support]: https://github.com/rust-lang/rust/tree/master/src/tools/run-make-support
+[bootstrap]: https://github.com/rust-lang/rust/tree/master/src/bootstrap
+[libtest]: https://github.com/rust-lang/rust/tree/master/library/test
+[new-issue]: https://github.com/rust-lang/rust/issues/new
+[filecheck]: https://llvm.org/docs/CommandGuide/FileCheck.html
+[run-make]: https://github.com/rust-lang/rust/tree/master/tests/run-make
+[tidy]: https://github.com/rust-lang/rust/tree/master/src/tools/tidy
+
+
+[^lldb]: For example, I keep having to debug the debugger like `lldb` when the older `lldb` versions keep complaining about `ModuleNotFoundError: No module named '_lldb'`.
+[^nocapture]: I don't know about you, but I can never for the life of me remember what the flag is called. I keep thinking it's `--no-capture` when currently libtest only accepts `--nocapture`. Thankfully T-testing-devex FCP'd to add the more conventional version `--no-capture`, looking forward to that. I can also never figure out how many `--` dashes I need, I keep finding myself having to add more `--` until it starts working.
+[^oops]: Nyehehehe