f1ed13efff
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.
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forErrors.lean:3:29-3:30: error: failed to synthesize instance
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ToStream α ?m
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