lean4-htt/tests/lean/run/issue8213.lean
Joachim Breitner 6b7a803bf4
fix: mapError to store message data context (#8375)
This PR ensures that using `mapError` to expand an error message uses
`addMessageContext` to include the current context, so that expressions
are rendered correctly. Also adds a `preprendError` variant with a more
convenient argument order for the common cases of
prepending-and-indenting.
2025-05-16 14:46:23 +00:00

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-- set_option trace.Meta.FunInd true
def myTest {α}
(mmotive : (x : List α) → Sort v)
(x : List α)
(h_1 : (a : α) → (dc : List α) → x = a :: dc → mmotive (a :: dc))
(h_2 : (x' : List α) → x = x' → mmotive x') : mmotive x :=
match (generalizing := false) h : x with
| a :: dc => h_1 a dc h
| x' => h_2 x' h
/--
error: Failed to realize constant myTest.fun_cases:
Cannot derive functional cases principle (please report this issue)
failed to transform matcher, type error when constructing new pre-splitter motive:
myTest.match_1 (fun x => motive x h_1 h_2) x
failed with
Application type mismatch: In the application
motive x✝ h_1
the argument
h_1
has type
(a : α) → (dc : List α) → x = a :: dc → mmotive (a :: dc) : Sort (imax (u_1 + 1) (u_1 + 1) v)
but is expected to have type
(a : α) → (dc : List α) → x✝ = a :: dc → mmotive (a :: dc) : Sort (imax (u_1 + 1) (u_1 + 1) v)
---
error: unknown identifier 'myTest.fun_cases'
-/
#guard_msgs in
def foo := @myTest.fun_cases