commit a31490d9a832b955410fd00b66c9b98f96e292df
author David Tolnay <dtolnay@gmail.com> Thu Jan 05 03:08:45 2023 -0800
committer GitHub <noreply@github.com> Thu Jan 05 11:08:45 2023 +0000
tree b5d71136b9c86a661ef6ccc96ccb5d103acec265
parent 7ebad4d501e9a5873befcbf762349b1870ad44ed

Make loads from @rules_rust//rust:defs.bzl come out on one line (#1753)

At first I was confused why some of the generated files were coming out with loads formatted like this:

https://github.com/bazelbuild/rules_rust/blob/4ef3d4aaa27569616d9d085b0b01b4f155c09675/crate_universe/3rdparty/crates/BUILD.anyhow-1.0.68.bazel#L9-L13

Surely this should be as follows? The wrapped line is even shorter than the unwrapped line.

```bzl
load("@rules_rust//cargo:defs.bzl", "cargo_build_script")
load("@rules_rust//rust:defs.bzl", "rust_library")
```

It turned out to be because crate_universe unconditionally generates _all_ the loads that might be needed:

```bzl
load("@rules_rust//cargo:defs.bzl", "cargo_build_script")
load(
    "@rules_rust//rust:defs.bzl",
    "rust_library",
    "rust_binary",
    "rust_proc_macro",
)
```

and then Buildifier deletes any that are unused, but without rewrapping any lines:

```bzl
load("@rules_rust//cargo:defs.bzl", "cargo_build_script")
load(
    "@rules_rust//rust:defs.bzl",
    "rust_library",
)
```

This PR tweaks crate_universe to generate only loads that are used, so that we retain control over how they are wrapped. After this PR, single loads get put on one line while multiple loads get put on multiple lines.

https://github.com/bazelbuild/rules_rust/blob/e987f2041df8abed1897ab3684a7af3158adee34/crate_universe/3rdparty/crates/BUILD.anyhow-1.0.68.bazel#L9-L10

https://github.com/bazelbuild/rules_rust/blob/e987f2041df8abed1897ab3684a7af3158adee34/bindgen/3rdparty/crates/BUILD.bindgen-0.60.1.bazel#L9-L14