03bd8847dc
This PR fixes the termination checker reporting errors at the wrong recursive call site when a function contains structurally-identical recursive calls at different source locations. The `_recApp` `MData` attached to recursive applications carried the attached `Syntax`, but two structurally-equal `MData` wrappers could be merged by hashconsing/simplification, so the syntax of the first call ended up associated with both call sites. We now also store the source byte position as `_recAppPos`, which keeps the wrappers distinct. Closes #13444.
32 lines
975 B
Text
32 lines
975 B
Text
module
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/-!
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The termination error should be reported at the second recursive call, not the first.
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The two calls `f heapsize (lCh i)` are structurally identical syntax; without recording
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the source position in the `_recApp` mdata, hashconsing/simplification merged them and
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the error was attributed to the wrong call.
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-/
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def lCh := (· * 2 + 1)
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/--
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@ +7:6...24
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error: failed to prove termination, possible solutions:
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- Use `have`-expressions to prove the remaining goals
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- Use `termination_by` to specify a different well-founded relation
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- Use `decreasing_by` to specify your own tactic for discharging this kind of goal
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heapsize i : Nat
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h✝¹ : i < heapsize
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h✝ : ¬i = 0
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⊢ heapsize - lCh i < heapsize - i
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-/
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#guard_msgs (positions := true) in
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def f (heapsize i : Nat) : Nat :=
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if i < heapsize then
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if i = 0 then
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have : i < lCh i := by simp [lCh]; omega
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f heapsize (lCh i)
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else
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f heapsize (lCh i)
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else 0
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termination_by heapsize - i
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