Bootstrap vendoring requires `rustc-perf` submodule (unconditionally?)

[jieyouxu]

[...] it seems this patch has broken our Rust mirror for Fuchsia. We've had to exclude rustc-perf from our local mirror since it has a pretty complicated licensing story. Rust previously built fine for us since we weren't running the performance tests, but with this patch we're now getting this error:

submodule src/tools/rustc-perf does not appear to be checked out, but it is required for
this step.

Consider setting `build.submodules = true` or manually initializing the submodules.

Is there any way we could work around this, or add a flag where we could skip this check?

Originally posted by @erickt in #137020 (comment)

[jieyouxu]

cc @pietroalbini @Kobzol: I feel like it's "more correct" (at least safer license wise) for copyright generation to collect all licenses transitively (including by explicitly checking out submodules) as done in #137020. Unless we modify the copyright generation logic to somehow keep track of what tools that some dist configuration may never use (at the risk of this diverging and oops license violation)?

[Kobzol]

Yeah, I think that we should collect everything, just to make sure we don't miss stuff.

[jieyouxu]

@erickt can Fuchsia checkout the src/tools/rustc-perf submodule beforehand?

[Sandlot19]

Hi - I'm working with Erick on the Fuchsia side to get this resolved. Our open source licensing approval process prevents us from checking out src/tools/rustc-perf since it has no top level LICENSE file (Erick please correct me if I'm wrong). Without that top level file, we cannot checkout the submodule without a more involved approval process and doing some additional work on our mirror (which doesn't exist yet).

[Kobzol]

Hi, rustc-perf uses REUSE (https://github.com/rust-lang/rustc-perf/tree/master/LICENSES, https://github.com/rust-lang/rustc-perf/blob/master/REUSE.toml), which should be even more comprehensive than just a single top-level license file. The Rust compiler now also uses REUSE, btw.

[erickt]

Hi folks, I talked with our internal opensource team, and it sounds like our internal tooling is blocked on licensee/licensee#737 / fsfe/reuse-tool#901 and so it can't interpret the REUSE.toml at the moment, and it'd take some some time to get that implemented. Our other supported option would be to instead use our internal mechanism that'd fork rustc-perf (and rust) to construct the top-level LICENSE file for us derived off teh REUSE.toml-based files. The biggest downside there is that'd change our git hashes, complicate how we create our stage0 builds, and make it more challenging for us to coordinate with upstream rust on bugs.

I know this is a situation caused by my company and not Rust, but if it'd really help us out in the meantime if we could re-land the equivalent to rust-lang/rustc-perf#1881 to add back the top-level LICENSE.

[Kobzol]

Well, the problem is that the previous top level license was outright wrong, and did not accurately describe what was in the repository.. :) So it would be a technical solution for your tooling to work, but it would also be inaccurate from the licensing standpoint.

@Mark-Simulacrum Thoughts?