Currently the json-formatted outputs have no way to unambiguously
determine which kind of message is being output. A consumer can look for
specific fields in the json object (eg "message"), but there's no
guarantee that in future some other kind of output will have a field of
the same name.
This PR adds a `"type"` field to add json outputs which can be used to
unambiguously determine which kind of output it is. The mapping is:
diagnostic: regular compiler diagnostics
artifact: artifact notifications
future_incompat: Report of future incompatibility
unused_extern: Unused crate warnings/errors
This matches the "internally tagged" representation for serde enums.
This option guards the logic of writing long type names in files and
instead using short forms in error messages in rustc_middle/ty/error
behind a flag. The main motivation for this change is to disable this
behaviour when running ui tests.
This logic can be triggered by running tests in a directory that has a
long enough path, e.g. /my/very-long-path/where/rust-codebase/exists/
This means ui tests can fail depending on how long the path to their
file is.
Some ui tests actually rely on this behaviour for their assertions,
so for those we enable the flag manually.
