80a85cd3d9
This PR fixes a regression introduced in #7166 where, after fixed and varying parameters were allowed to be reordered, three places in `Lean.Elab.Structural.FindRecArg` still indexed the concatenation `xs ++ ys` with `recArgInfo.recArgPos` even though `recArgPos` refers to the original parameter order. With fixed parameters interleaved with the structural argument, this picked the wrong element: error messages named the wrong parameter, and `argsInGroup`'s nested-inductive recognition silently rejected otherwise-valid mutual definitions. All three sites now use `recArgInfo.fixedParamPerm.buildArgs xs ys` so the index matches `recArgPos` and `indicesPos`. Closes #13729.
56 lines
1.8 KiB
Text
56 lines
1.8 KiB
Text
/-!
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Regression tests for issue #13729.
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After PR #7166, `termination_by structural` runs the structural-recursion
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analysis on parameters reordered with `FixedParamPerm.buildArgs xs ys`, so
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`recArgInfo.recArgPos` indexes into that array (the original parameter
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order). Three places in `FindRecArg.lean` instead concatenated `xs ++ ys`
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(fixed parameters first) and dereferenced with `recArgPos`, picking the
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wrong element whenever fixed and varying parameters were interleaved.
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-/
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inductive Tree where
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| leaf : Tree
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| node : Tree → Tree → Tree
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/--
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error: failed to infer structural recursion:
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Cannot use parameter h:
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failed to eliminate recursive application
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test (m + 1) (h.node h) c
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-/
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#guard_msgs in
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def test (m : Nat) (h : Tree) (c : Bool) : Nat :=
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match h with
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| .leaf => m
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| .node _ _ => test (m+1) (Tree.node h h) c
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termination_by structural h
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/-!
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Nested-inductive case exercising the same bug in
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`argsInGroup` (the second/third occurrences). `Tree₂.sizeList`'s structural
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argument has type `List Tree₂` while the relevant inductive group is `Tree₂`,
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so `argsInGroup` must recognize the argument as a nested type former. Picking
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the wrong element of the parameter array (i.e. `c` instead of `ts`) would make
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that recognition fail and reject the definition.
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-/
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inductive Tree₂ where
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| node : List Tree₂ → Tree₂
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mutual
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def Tree₂.size (m : Nat) (t : Tree₂) (c : Bool) : Nat :=
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match t with
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| .node ts => Tree₂.sizeList m ts c + 1
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termination_by structural t
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def Tree₂.sizeList (m : Nat) (ts : List Tree₂) (c : Bool) : Nat :=
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match ts with
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| [] => 0
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| t :: rest => Tree₂.size m t c + Tree₂.sizeList m rest c
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termination_by structural ts
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end
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/-- info: 4 -/
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#guard_msgs in
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#eval Tree₂.size 0 (.node [.node [], .node [.node []]]) true
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