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#2905
Followup to #5841. Makes the `structure` command populate the new
`parentInfo` field with all the structures in the `extends` clause.
This will require a stage0 update to fully take effect.
Breaking change: now it's a warning if a structure extends a parent
multiple times.
Breaking change: now `getParentStructures` is `getStructureSubobjects`.
Adds `getStructureParentInfo` for getting all the immediate parents.
Note that the set of subobjects is neither a subset nor a superset of
the immediate parents.
Closes#1881
Floris van Doorn [reported on
Zulip](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/have.20tactic.20error.20recovery/near/425283053)
that it is confusing that the `have : T := e` tactic completely fails if
the body `e` is not of type `T`. This is in contrast to `have : T := by
exact e`, which does not completely fail when `e` is not of type `T`.
This ends up being caused by `elabTermEnsuringType` throwing an error
when it fails to insert a coercion. Now, it detects this case, and it
checks the `errToSorry` flag to decide whether to throw the error or to
log the error and insert a `sorry`.
This is justified by `elabTermEnsuringType` being a frontend to
`elabTerm`, which inserts `sorry` on error.
An alternative would be to make `ensureType` respect `errToSorry`, but
there exists code that expects being able to catch when `ensureType`
fails. Making such code manipulate `errToSorry` seems error prone, and
this function is not a main entry point to the term elaborator, unlike
`elabTermEnsuringType`.
