On
[Zulip](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/Notation.20in.20namespace.20not.20showing.20in.20pp/near/437016468),
Peter Nelson reported that notations that could be pretty printed with
generalized field notation did not pretty print using the intended
notation.
This PR makes it so that app unexpanders are considered before
generalized field notation. The complexity before was that we wanted to
do parent projection collapse, and since we did the collapse before
pretty printing that argument, it meant it wasn't possible to do app
unexpanders when there was a field notation candidate. The new solution
is to collapse parent projections only when actually considering field
notation, which can be done because we can safely strip off projection
syntax in an expression-directed way.
Sets the default value to `pp.fieldNotation.generalized` to `true`.
Updates tests, and fixes some minor flaws in the implementation of the
generalized field notation pretty printer.
Now generalized field notation won't be used for any function that has a
`motive` argument. This is intended to prevent recursors from pretty
printing using it as (1) recursors are more like control flow structures
than actual functions and (2) generalized field notation tends to cause
elaboration problems for recursors.
Note: be sure functions that have an `@[app_unexpander]` use
`@[pp_nodot]` if applicable. For example, `List.toArray` needs
`@[pp_nodot]` to ensure the unexpander prints it using `#[...]`
notation.
Refactors app delaborator, merging in the projection delaborator, to
support pretty printing with generalized field notation.
Renames option `pp.structureProjections` to `pp.fieldNotation` and adds
sub-option `pp.fieldNotation.generalized` to enable/disable generalized
field notation. Adds `@[pp_nodot]` attribute to permanently disable
using field notation for a given declaration.
For now, the default value of `pp.fieldNotation.generalized` is false
since we need a stage0 update to add `@[pp_nodot]` to some core
definitions (such as `List.toArray`) before updating the tests.
[Zulip
discussion](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/.60pp.2EgeneralizedFieldNotation.60/near/425856054)
