rustdoc tests error output without tidy is very bad

[tmandry]

Note: tidy here is the html diff / format tool, not src/tools/tidy

From the 1.52 retrospective: Having this installed would have made it much easier to spot the issue in #84950.

[jyn514]

"depend" is not quite correct - tests will pass fine without it, but if they fail the error message is very bad.

[GuillaumeGomez]

We improved the error message in case tidy isn't installed to avoid showing up the HTML diff, so let's say it's less good and more difficult to understand.

[GuillaumeGomez]

I think we can close it since it's possible to run rustdoc tests without tidy installed.

[jyn514]

"depend" is not quite correct - tests will pass fine without it, but if they fail the error message is very bad.

@GuillaumeGomez this problem is still not solved.

[GuillaumeGomez]

Renaming the issue to reflect this then.

[jyn514]

@tmandry A simple solution is to just install tidy on the release builders. I don't know how to do that but it's packaged in nearly every distro.

[lolbinarycat]

at the very least the "tidy is not installed" message should link to the tool's homepage so it can be installed.

this is especially confusing because of the existence of the tidy tool.