commit 828c8071f39aa94a3bcfebb391b864aeb41453e9
author UebelAndre <github@uebelandre.com> Wed Dec 27 09:02:43 2023 -0800
committer GitHub <noreply@github.com> Wed Dec 27 17:02:43 2023 +0000
tree 4eada66d22b8683c860dc6710c3f35dd9522fdd1
parent 6a9359232eff24fa6f30978ac2d84bef615d591d

Added `rust_unpretty_aspect` and `rust_unpretty` rules (#2356)

Proposal for https://github.com/bazelbuild/rules_rust/issues/1642
Duplicates https://github.com/bazelbuild/rules_rust/pull/1643 (special
thanks to @freeformstu)

### Summary

Rustc can be used to expand all macros so that you can inspect the
generated source files easier.

This feature is enabled via `-Zunpretty={mode}`. The `-Z` flag is only
available in the nightly
version of `rustc` (https://github.com/rust-lang/rust/issues/43364).


### Unprettying

Build and test your targets normally.

```
bazel build //:ok_binary   
INFO: Analyzed target //:ok_binary (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //:ok_binary up-to-date:
  bazel-bin/ok_binary
INFO: Elapsed time: 0.081s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
```

Use the aspect to generate the expanded files in as a one-off build.

(`.bazelrc`)
```
# Enable unpretty for all targets in the workspace
build:unpretty --aspects=@rules_rust//rust:defs.bzl%rust_unpretty_aspect
build:unpretty --output_groups=+rust_unpretty

# `unpretty` requires the nightly toolchain. See tracking issue:
# https://github.com/rust-lang/rust/issues/43364
build:unpretty --@rules_rust//rust/toolchain/channel=nightly
```

```
bazel build --config=unpretty //:ok_binary
INFO: Analyzed target //:ok_binary (1 packages loaded, 2 targets configured).
INFO: Found 1 target...
Aspect @rules_rust//rust/private:unpretty.bzl%rust_unpretty_aspect of //:ok_binary up-to-date:
  bazel-bin/ok_binary.expand.rs
INFO: Elapsed time: 0.149s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
```

Targeting tests is valid as well.

```
bazel build --config=unpretty //:ok_test  
INFO: Analyzed target //:ok_test (0 packages loaded, 2 targets configured).
INFO: Found 1 target...
Aspect @rules_rust//rust/private:unpretty.bzl%rust_expand_aspect of //:ok_test up-to-date:
  bazel-bin/test-397521499/ok_test.expand.rs
INFO: Elapsed time: 0.113s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
```

Finally, manually wire up a `rust_unpretty` target explicitly if you
want a target to build. This rule is unique compared to the aspect in
that it forces a transition to a nightly toolchain so that `-Zunpretty`
can be used.

```starlark
load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_unpretty")

rust_binary(
    name = "ok_binary",
    srcs = ["src/main.rs"],
    edition = "2021",
)

rust_unpretty(
    name = "ok_binary_expand",
    deps = [":ok_binary"],
)
```

```
bazel build //:ok_binary_expand
INFO: Analyzed target //:ok_binary_expand (0 packages loaded, 1 target configured).
INFO: Found 1 target...
Target //:ok_binary_expand up-to-date:
  bazel-bin/ok_binary.expand.rs
INFO: Elapsed time: 0.090s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
```