Remove `missing_tools` config

[Gankra]

The scope of this issue changed; see here for the current status.

Original issue description for historians:

---

config.toml lets you request tools be built, and it lets you ignore build failures with dist.missing-tools = true, but it doesn't let you specify that some packages must be built, while others are ok to miss.

Ideally, it would support either an optional-tools array, or missing-tools could take an array of tools that are ok to miss, so that this nuance could be expressed.

This is a little niche, but I'm running into this while hooking up a "build rust from source" option in firefox's CI, where rustfmt is optional but nice-to-have for lints. Currently I think the best option is to using missing-tools = true and check the output for warnings about skipped tools in the dist step. This is a bit fragile though, so it would be nice if this was built in.

@Mark-Simulacrum mentionned this would also be desirable for miri on stable/beta?

[RalfJung]

@Mark-Simulacrum mentionned this would also be desirable for miri on stable/beta?

That might be related to #74709.

[jyn514]

This is a little niche, but I'm running into this while hooking up a "build rust from source" option in firefox's CI, where rustfmt is optional but nice-to-have for lints. Currently I think the best option is to using missing-tools = true and check the output for warnings about skipped tools in the dist step. This is a bit fragile though, so it would be nice if this was built in.

Note that rustfmt always compiles successfully now, and miri should too. So I'm not sure missing-tools is useful at all anymore? I can't think of anything that would fail to build.

[jyn514]

Mentoring instructions:

1. Change ToolBuild to unconditionally require tools to build:

   rust/src/bootstrap/tool.rs

   Line 80 in 11e002a

   let is_expected = compile::stream_cargo(builder, cargo, vec![], &mut |msg| {

   . Please also switch from stream_cargo to run_cargo at the same time to avoid duplicating code.
2. Change the Output for ToolBuild to be PathBuf instead of Option<PathBuf>.
3. Remove the is_optional_tool field from ToolBuild
4. Remove the missing_tools field from Config and Dist - it doesn't seem to do anything since 6cfa7ef.

[tharunsuresh-code]

I can take this up if no one else is working on it.

• If I understand correctly, changing to run_cargo requires changing the function arguments (Quoted above)? I am not sure if it is a trivial change here
• Also, changing Output to PathBuf requires a cascading change in the following functions in which it is called?
• There are no missing tools in Dist I believe.

I am kinda new here, so any help would be much appreciated.