compiletest: Improve diagnostics for line annotation mismatches

[petrochenkov]

When some line annotations are missing or misplaced, compiletest reports an error, but the error is not very convenient.
This PR attempts to improve the user experience.

• The "expected ... not found" messages are no longer duplicated.
• The proc_res.status and proc_res.cmdline message is no longer put in the middle of other messages describing the annotation mismatches, it's now put into the end.
• Compiletest now makes suggestions if there are fuzzy matches between expected and actually reported errors (e.g. the annotation is put on a wrong line).
• Missing diagnostic kinds are no longer produce an error eagerly, but instead treated as always mismatching kinds, so they can produce suggestions telling the right kind.

I'll post screenshots in the thread below, but the behavior shown on the screenshots can be reproduced locally using the new test tests/ui/compiletest-self-test/line-annotation-mismatches.rs.

r? @jieyouxu

[rustbot]

Some changes occurred in src/tools/compiletest

cc @jieyouxu

[petrochenkov]

Before: that's the only shown error when some annotation kind is missing.

[petrochenkov]

Before: without missing annotation kinds (some stuff at the top is cropped, but the picture is clear).

[petrochenkov]

After: with top and bottom messages merged, and suggestions added.

[jieyouxu]

Nice! I'll play around with this tmrw on Monday.

[bors]

☔ The latest upstream changes (presumably #140599) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

@jieyouxu
By the way, do you think the line1:column1: line2:column2: part is useful in error messages?

I does two things

• it's displayed in annotation mismatch messages, but it mostly duplicates the file:line part which is also displayed.
  • the column part could be slightly useful in the past when we didn't have UI tests with captured .stderr, but probably not now
• it can actually be matched in line annotations, e.g. you can write //~ ERROR 28:16: cannot find value, but it seems to be an antipattern

Also, this part is not always added, it's only added to primary diagnostics, but not to labels or suggestions, for example.

I think maybe just drop it to reduce noise and duplication.
(The column can be moved to file:line:column instead of being fully dropped, if necessary.)

[petrochenkov]

Another possible improvement is to display relative paths to test files instead of absolute paths, also to avoid noise, duplication and rightward shift.

The main requirement for the paths is to be "clickable", so you can quickly go from a file:line string in shell to that file and line in editor.

Relative paths here would work for me (vscode + rust is the only directory open in the workspace), but I'm not sure what other setups people can use.