This PR adds the new transparency setting `@[instance_reducible]`. We
used to check whether a declaration had `instance` reducibility by using
the `isInstance` predicate. However, this was not a robust solution
because:
- We have scoped instances, and `isInstance` returns `true` only if the
scope is active.
- We have auxiliary declarations used to construct instances manually,
such as:
```lean
def lt_wfRel : WellFoundedRelation Nat
```
`isInstance` also returns `false` for this kind of declaration.
In both cases, the declaration may be (or may have been) used to
construct an instance, but `isInstance`
returns `false`. Thus, we claim it is a mistake to check the
reducibility status using `isInstance`.
`isInstance` indicates whether a declaration is available for the type
class resolution mechanism,
not its transparency status.
**We are decoupling whether a declaration is available for type class
resolution from its transparency status.**
**Remak**: We need a update stage0 to complete this feature.
---------
Co-authored-by: Sebastian Ullrich <sebasti@nullri.ch>
This PR makes `#guard_msgs` to treat `trace` messages separate from
`info`, `warning` and `error`. It also introduce the ability to say
`#guard_msgs (pass info`, like `(drop info)` so far, and also adds
`(check info)` as the explicit form of `(info)`, for completeness.
Fixes#8266
Currently, the messages in the diagnostic summaries are created by
appending interpolated strings. We wrap these in `.trace`'s, and the
results are better formatted when expanding child nodes in the info
view. Particularly, the latter diagnostic summaries remain on their own
lines flush to the left instead of on the same line directly adjacent to
the last child node.
