add an extension point in bootstrap.toml for metadata?

[jyn514]

Summary

Ferrocene maintains a fork of bootstrap with different configuration options than upstream. We put these under a [ferrocene.*] table, which means that using a ferrocene-specific config.toml with an upstream branch causes bootstrap to error.

Does t-bootstrap have any interest in adding a [metadata] field with arbitrary data here so that we can hook onto it, like package.metadata in Cargo.toml? We don't need you to do anything at all with it, just parse the TOML and discard it. I'm happy to make a PR implementing the code.

Command used

x build

Expected behaviour

[custom options are ignored]

Actual behaviour

ERROR: Failed to parse '/Users/jyn/src/rust-upstream/config.toml': unknown field `ferrocene`

Bootstrap configuration (bootstrap.toml)

[ferrocene.example]
option = true

Operating system

macOS Version 15.5 (24F74) Darwin 24.5.0

HEAD

2adaa5d

[jyn514]

@rustbot label -C-bug +C-enhancement

[Kobzol]

I guess that the only downside is that we would then have to ignore unknown sections instead of erroring out in them, which is not ideal.

If everything was scoped under a known "blackbox" section, such as [metadata], then it would be fine.

[jyn514]

Yup exactly, I'm asking for a metadata section. I'm happy for bootstrap to continue erroring on other unknown keys.

[Kobzol]

Ah, ok, that wasn't clear from the expected behavior section. Yeah, if there was an opaque metadata field, I'd be fine with that.