3acd77a154
Floris van Doorn [reported on Zulip](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/have.20tactic.20error.20recovery/near/425283053) that it is confusing that the `have : T := e` tactic completely fails if the body `e` is not of type `T`. This is in contrast to `have : T := by exact e`, which does not completely fail when `e` is not of type `T`. This ends up being caused by `elabTermEnsuringType` throwing an error when it fails to insert a coercion. Now, it detects this case, and it checks the `errToSorry` flag to decide whether to throw the error or to log the error and insert a `sorry`. This is justified by `elabTermEnsuringType` being a frontend to `elabTerm`, which inserts `sorry` on error. An alternative would be to make `ensureType` respect `errToSorry`, but there exists code that expects being able to catch when `ensureType` fails. Making such code manipulate `errToSorry` seems error prone, and this function is not a main entry point to the term elaborator, unlike `elabTermEnsuringType`.
24 lines
388 B
Text
24 lines
388 B
Text
/-!
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# Tests for the `have` tactic.
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-/
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/-!
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If the body of a `have` fails to elaborate, the tactic completes with a `sorry` for the proof.
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-/
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/--
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error: type mismatch
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False.elim
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has type
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False → ?m.6 : Sort ?u.5
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but is expected to have type
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True : Prop
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---
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info: h : True
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⊢ True
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-/
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#guard_msgs in
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example : True := by
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have h : True :=
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False.elim
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trace_state
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assumption
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