fix: make delta-derived Prop-valued instances theorems#13304
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This PR makes the delta-deriving handler create `theorem` declarations instead of `def` declarations when the instance type is a `Prop`. Previously, `deriving instance Nonempty for Foo` would always create a `def`, which is inconsistent with the behavior of a handwritten `instance` declaration. Closes #13295 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Nice! Though, we should avoid setting |
Address review feedback: skip setting `@[implicit_reducible]` on Prop-valued instances (theorems), matching the behavior of the handwritten `instance` command in `MutualDef.lean`. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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This PR makes the delta-deriving handler create `theorem` declarations instead of `def` declarations when the instance type is a `Prop`. Previously, `deriving instance Nonempty for Foo` would always create a `def`, which is inconsistent with the behavior of a handwritten `instance` declaration. For example, given: ```lean def Foo (α : Type u) := List α deriving instance Nonempty for Foo ``` Before: `@[implicit_reducible] def instNonemptyFoo ...` After: `@[implicit_reducible] theorem instNonemptyFoo ...` The implementation checks `isProp result.type` after constructing the instance closure, and uses `mkThmOrUnsafeDef` for the Prop case (which also handles the unsafe fallback correctly). The noncomputable check is skipped for Prop-typed instances since theorems can freely reference noncomputable constants. Closes #13295 🤖 Prepared with Claude Code --------- Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com> (cherry picked from commit 30dca7b)
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This PR makes the delta-deriving handler create
theoremdeclarations instead ofdefdeclarations when the instance type is aProp. Previously,deriving instance Nonempty for Foowould always create adef, which is inconsistent with the behavior of a handwritteninstancedeclaration.For example, given:
Before:
@[implicit_reducible] def instNonemptyFoo ...After:
@[implicit_reducible] theorem instNonemptyFoo ...The implementation checks
isProp result.typeafter constructing the instance closure, and usesmkThmOrUnsafeDeffor the Prop case (which also handles the unsafe fallback correctly). The noncomputable check is skipped for Prop-typed instances since theorems can freely reference noncomputable constants.Closes #13295
🤖 Prepared with Claude Code