Diff on rustdoc test failure does not work on Windows

[rylev]

When running x .py test .\src\test\rustdoc on Linux and a failure happens, a really nice diff of the output vs rustdoc-nightly is produced which very clearly shows the issue. This does not work on Windows for multiple reasons.

One the call to diff fails:

info: generating a diff against nightly rustdoc
warning: no pager configured, falling back to `diff --color`
help: try configuring a git pager (e.g. `delta`) with `git config --global core.pager delta`
thread '[rustdoc] rustdoc\sidebar-link-generation.rs' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }', src\tools\compiletest\src\runtest.rs:2467:55

Second, the output from rustdoc-nightly seems to exactly match that from the local compiler making it not possible to do manual diffs.

[jyn514]

One the call to diff fails:

How do you diff directories recursively on Windows? On Linux I would be very surprised for diff not to be installed.

The output from rustdoc-nightly seems to exactly match that from the local compiler

Oh I just thought of something - do you have a rustup overide that defaults to your local toolchain? Right now compiletest assumes the default is nightly, I've been meaning to change it.

[rylev]

do you have a rustup overide that defaults to your local toolchain?

No, I only set overrides on specific projects (and rust-lang/rust is not one of them). My default is the stable compiler.

[mati865]

Git for Windows provides diff:

$ which diff
/usr/bin/diff

Are you building Rust using Git Bash prompt?

[rylev]

I don't think it'd be a good idea to require testing rustdoc in the Git for Windows bash shell. I'd like for this to work in cmd.exe and PowerShell if possible.