Many of our tests in `tests/lean/run/` produce output from `#eval` (or
`#check`) statements, that is then ignored.
This PR tries to capture all the useful output using `#guard_msgs`. I've
only done a cursory check that the output is still sane --- there is a
chance that some "unchecked" tests have already accumulated regressions
and this just cements them!
In the other direction, I did identify two rotten tests:
* a minor one in `setStructInstNotation.lean`, where a comment says `Set
Nat`, but `#check` actually prints `?_`. Weird?
* `CompilerProbe.lean` is generating empty output, apparently indicating
that something is broken, but I don't know the signficance of this file.
In any case, I'll ask about these elsewhere.
(This started by noticing that a recent `grind` test file had an
untested `trace_state`, and then got carried away.)
We now (try to) postpone `match ... with` elaboration when pattern
variables and patterns still contain metavariables before invoking `mkMatcher`.
This improvement makes sure we can elaborate an example submitted by
Daniel Selsam.
Remark: this update may create performance problems since we
backtrack `elabMatchTypeAndDiscrs` and `elabMatchAltView`.
We hope this is not a problem in practice since we use the "quick-check"
`waitExpectedTypeAndDiscrs`. Recall that we could compile Lean
without this commit. So, it suggests cases where we need to postpone
after `elabMatchAltView` are rare.
