Add option to anonymize line numbers

[phansch]

With the current diagnostics emitter of Rust, the -Z ui-testing flag
allows to 'anonymize' line numbers in the UI test output.

This means that a line such as:

 2 |     concat!(b'f');

is turned into:

LL |     concat!(b'f');

This is done because it makes the diff of UI test output changes much
less noisy.

To support this with annotate-snippet, we add a second parameter to
DisplayListFormatter that, when true, replaces the line numbers in the
left column with the text LL. The replacement text is always LL and
it does not affect the initial location line number.

In the new annotate-snippet emitter in rustc, we can then use this
parameter depending on whether the -Z ui-testing flag is set or not.

Closes #2
cc rust-lang/rust#59346

[phansch]

One of my small gripes with Rust is that it doesn't have keyword arguments (yet?). That would make passing these boolean options much more understandable at the call sites. I'm not sure if there's currently a clearer way?

[oli-obk]

keyword arguments

you can always create structs with appropriate field names ;)

[phansch]

Replaced the magic constant.

@zbraniecki what are your feelings regarding the change of the api of the DisplayListFormatter constructor? I feel like it's still fine when passing two booleans. If there turns out to be a need for more configuration, it could be changed later?

[zbraniecki]

If there turns out to be a need for more configuration, it could be changed later?

Yep, it's an internal API, I'm fine with adjusting it later.

[oli-obk]

I wonder...

@bors r+

[oli-obk]

I guess not

[phansch]

Thanks! I think this will also need a new release before it can be used in rustc, right?

[phansch]

@zbraniecki (or someone else?) could you push a new version to crates.io?

[zbraniecki]

yeah, will do.

[zbraniecki]

done. 0.6.0 released.

[zbraniecki]

@phansch did you intend to turn also context lines (without numbers) to LL?

I see this:

error[E0003]: Expected token: "="
 --> ../fluent-bundle/examples/resources/en-US/simple.ftl:2:18
  |
2 | input-parse-error Error: Could not parse input `{ $input }`. Reason: { $reason }
  |                   ^^ Expected token: "="
  |
-----------------------------

turned into:

error[E0003]: Expected token: "="
  --> ../fluent-bundle/examples/resources/en-US/simple.ftl:2:18
LL |
LL | input-parse-error Error: Could not parse input `{ $input }`. Reason: { $reason }
LL |                   ^^ Expected token: "="
LL |
-----------------------------

I think I'd expect:

error[E0003]: Expected token: "="
  --> ../fluent-bundle/examples/resources/en-US/simple.ftl:2:18
   |
LL | input-parse-error Error: Could not parse input `{ $input }`. Reason: { $reason }
   |                   ^^ Expected token: "="
   |
-----------------------------

instead.

[phansch]

Yeah I noticed that, too. That's a bug of the current implementation. My current plan is to only show LL for DisplaySourceLine::Content and where DisplayLine::Source has a lineno set. I think that should be enough?

(I've been a bit time restricted the past month or so but I want to get back into it again this month)