This PR scans the environment for viable replacements for a dotted
identifier (like `.zero`) and suggests concrete alternatives as
replacements.
## Example
```
#example .zero
```
Error message:
```
Invalid dotted identifier notation: The expected type of `.cons` could not be determined
```
Additional hint added by this PR:
```
Hint: Using one of these would be unambiguous:
[apply] `BitVec.cons`
[apply] `List.cons`
[apply] `List.Lex.cons`
[apply] `List.Pairwise.cons`
[apply] `List.Perm.cons`
[apply] `List.Sublist.cons`
[apply] `List.Lex.below.cons`
[apply] `List.Pairwise.below.cons`
[apply] `List.Perm.below.cons`
[apply] `List.Sublist.below.cons`
[apply] `Lean.Grind.AC.Seq.cons`
```
## Additional changes
This PR also brings several related error message descriptions and code
actions more in line with each other, changing several "Suggested
replacement: " code actions to the more common "Change to " wording, and
sorts suggestions obtained from searching the context by the default
sort for Names (which prefers names with fewer segments).
This PR improves the error messages produced by invalid projections and
field notation. It also adds a hint to the "function expected" error
message noting the argument to which the term is being applied, which
can be helpful for debugging spurious "function expected" messages
actually caused by syntax errors.
---------
Co-authored-by: Joachim Breitner <mail@joachim-breitner.de>
This PR fixes a bug where the monad lift coercion elaborator would
partially unify expressions even if they were not monads. This could be
taken advantage of to propagate information that could help elaboration
make progress, for example the first `change` worked because the monad
lift coercion elaborator was unifying `@Eq _ _` with `@Eq (Nat × Nat)
p`:
```lean
example (p : Nat × Nat) : p = p := by
change _ = ⟨_, _⟩ -- used to work (yielding `p = (p.fst, p.snd)`), now it doesn't
change ⟨_, _⟩ = _ -- never worked
```
As such, this is a breaking change; you may need to adjust expressions
to include additional implicit arguments.
The elaboration function `Lean.Meta.coerceMonadLift?` inserts these
coercion helper functions into a term and tries to unfolded them with
`expandCoe`, but because that function only unfolds up to
reducible-and-instance transparency, these functions were not being
unfolded. The fix here is to give them the `@[reducible]` attribute.
