This already enables `download-rustc`, so it's quick to build rustdoc,
and this makes it less confusing when changes to rustdoc aren't reflected in the docs.
Note that this uses 2 and not 1 because `download-rustc` only affects stage 2 runs.
- Allow including defaults in `src/bootstrap/defaults` using `profile = "..."`
- Add default config files
- Combine config files using the merge dependency.
- Add comments to default config files
- Add a README asking to open an issue if the defaults are bad
- Give a loud error if trying to merge `.target`, since it's not
currently supported
- Use an exhaustive match
- Use `<none>` in config.toml.example to avoid confusion
- Fix bugs in `Merge` derives
Previously, it would completely ignore the profile defaults if there
were any settings in `config.toml`. I sent an email to the `merge` maintainer
asking them to make the behavior in this commit the default.
This introduces a new dependency on `merge` that hasn't yet been vetted.
I want to improve the output when `include = "x"` isn't found:
```
thread 'main' panicked at 'fs::read_to_string(&file) failed with No such file or directory (os error 2) ("configuration file did not exist")', src/bootstrap/config.rs:522:28
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failed to run: /home/joshua/rustc/build/bootstrap/debug/bootstrap test tidy
Build completed unsuccessfully in 0:00:00
```
However that seems like it could be fixed in a follow-up.
