This PR refines the new wording of the "application type mismatch" error
message to avoid ambiguity in references to the "final" argument in a
subexpression that may be followed by additional arguments.
It does so by replacing "final" with "last," rephrasing the message so
that this adjective modifies the argument itself rather than the word
"argument," and only displaying this wording when two arguments could be
confused (determined by expression equality).
These changes were motivated by a report that in cases where a function
application `f a b c` fails to elaborate because `b` is incorrectly
typed, the existing error message's reference to `b` being the "final"
argument in the application `f a b` may create confusion because it is
not the final argument in the full application expression.
This PR rewords the `application type mismatch` error message by more
specifically mentioning that the problem is with the final argument.
This is useful when the same argument is passed to the function multiple
times.
We decided against using a wording which specifically mentions the
"function expression", because users who are not used to currying might
not think of the `f a` in `f a b` as a function.
These commands were trusting that elaboration resulted in type-correct
terms, but users testing custom elaborators have found it to be
surprising that they do not do typechecking. This adds a `Meta.check`
step.
Closes#2736
See comment at `ExprDefEq.lean` for explanation.
Side effects:
- Improved error messages in two tests.
- Had to improve `getSuccesses` procedure at `App.lean`. It now
discards candidates that contain postponed elaboration problems.
If it is too disruptive for Mathlib, we should try to discard the
ones that have postponed metavariables.
