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Bug: GuessLex prints “Unexpected expression while unpacking n-ary argument” #3175

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nomeata opened this issue Jan 13, 2024 · 0 comments · Fixed by #3176
Closed

Bug: GuessLex prints “Unexpected expression while unpacking n-ary argument” #3175

nomeata opened this issue Jan 13, 2024 · 0 comments · Fixed by #3176
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@nomeata
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nomeata commented Jan 13, 2024

Description

GuessLex is confused by

def foo {n : Nat} (i : Fin n) : Bool := foo ⟨0, Nat.zero_lt_one⟩
decreasing_by decreasing_tactic

and prints

Unexpected expression while unpacking n-ary argument

No such error with

def foo {n : Nat} (i : Fin n) : Bool := foo ⟨0, Nat.zero_lt_one⟩
termination_by foo => sizeOf i
decreasing_by decreasing_tactic

Versions

4.5.0-rc1

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@nomeata nomeata added the bug Something isn't working label Jan 13, 2024
@nomeata nomeata mentioned this issue Jan 13, 2024
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github-merge-queue bot pushed a commit that referenced this issue Jan 13, 2024
@nomeata
fix: Fix/GuessLex: refine through more casesOnApp/matcherApp (#3176)
53af5ea 
there was a check

if !Structural.recArgHasLooseBVarsAt recFnName fixedPrefixSize e then

that would avoid going through `.refineThrough`/`.addArg` for
matcher/casesOn applications. It seems it tries to detect when refining
the motive/param is pointless, but it was too eager, and cause confusion
with, for example, this reasonably reasonable function:

    def foo : (n : Nat) → (i : Fin n) → Bool
      | 0, _ => false
      | 1, _ => false
      | _+2, _ => foo 1 ⟨0, Nat.zero_lt_one⟩
    decreasing_by simp_wf; simp_arith

In particular, the `GuessLex` code later expects that the (implict)
`PProd.casesOn` in the implementation of `foo._unary` will refine the
paramter, because else the (rather picky) `unpackArg` fails. But it also
prevents this from being provable.

So let's try without this shortcut.

Fixing this also revealed that `withRecApps` wasn’t looking in all
corners
of a matcherApp/casesOnApp.

Fixes #3175
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fix: Fix/GuessLex: refine through more casesOnApp/matcherApp leanprover/lean4
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