feat: only direct parents of classes create projections #5920
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Before, all class ancestors that were representable as subobject fields had their projections be instances. This (1) didn't include all direct parents and (2) might include indirect parents. Now, all direct parent classes are instances. Features: - Only parents that are not ancestors of other parents get instances. This allows "discretionary" indirect parents to be inserted without having an impact on typeclass synthesis for the purpose of computing strict resolution orders when `structure.strictResolutionOrder` is enabled. - Non-subobject projections are now theorems if the parent is a proposition. - Parent projections are no longer added as instances for the `structure` command. Only the `class` command`. Closes leanprover#2905
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| /-! | ||
| Check that `A` is not an instance, since it is implied by the others. | ||
| -/ | ||
| class E' extends C, D, A |
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This one surprises me a little; shouldn't it be an instance because the user asked for it in extends?
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(unless this emits a warning, in which case I have no objection besides the test not checking for that warning)
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No, there's no warning. This feature is necessary for being able to satisfy the strict C3 linearization algorithm in some cases without affecting what the actual instances are. Currently strict mode is not the default, but I hope we can refactor mathlib at some point to have a strict linearization.
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) This PR changes the rule for which projections become instances. Before, all parents along with all indirect ancestors that were represented as subobject fields would have their projections become instances. Now only projections for direct parents become instances. Features: - Only parents that are not ancestors of other parents get instances. This allows "discretionary" indirect parents to be inserted for the purpose of computing strict resolution orders when `structure.strictResolutionOrder` is enabled, without having an impact on typeclass synthesis. - Non-subobject projections are now theorems if the parent is a proposition. These are also no longer `@[reducible]`. Closes leanprover#2905
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This PR changes the rule for which projections become instances. Before, all parents along with all indirect ancestors that were represented as subobject fields would have their projections become instances. Now only projections for direct parents become instances.
Features:
structure.strictResolutionOrderis enabled, without having an impact on typeclass synthesis.@[reducible].Closes #2905