put it into a type class `BiPureForall`.

This property does not hold for embeddings of classical logic into Coq.

Previously, if would "cleanup" `<affine>` and `□` if the result after framing
is affine and intuitionistic, respectively. This behavior was inconsistent,
since similar "cleanup" was not performed for `<absorbing>` and `<persistent>`.
This MR thus removes this "cleanup" of modalities. It now consistently removes
the modalities `<affine>`, `<absorbing>, `<persistent>` and `□` only if the
result after framing is `True` or `emp`.

Since `iFrame` is already very complicated, and since its performance is
sometimes suboptimal in bigger developments, @jung and I believed doing
fewer "smart" things is better than the alternative, namely performing doing
sophisticated "cleanup" for all modalities, which is presented in
iris/iris!450

A failing iIntros for implications should prettify the identifier before
printing, and iIntros on something that isn't a wand or implication
should say what couldn't be introduced (to clarify that `iIntros "HP
HQ"` failed because of the HQ in particular, for example).

`iDestruct H as "H1 H2"` produces an error that says the pattern should
contain exactly one proper introduction pattern. When multiple patterns
are provided, due to Ltac variable shadowing iDestructHypFindPat was
instead reporting only the first pattern in the error message (and even
that was printed as the parsed AST rather than the original string).

The error handling for `iIntro (?)` and similar tactics didn't correctly
report failures when the goal couldn't be turned into a universal
quantifier. This is something missing from !482 due to no test
triggering the error.

The old code contained a bunch of unused spaghetti that was not cleaned up
after a refactoring.

@jihgfee menaged to trigger a wrong code path in the old code, but I failed
to turn his test case into a self-contained one.

Tej Chajed authored 4 years ago and Robbert Krebbers committed 4 years ago

Fixes #337.

Preserve identifiers in binders where possible, analogous to the support
for destructing existentials in !479.

Fixes #336.

Tej Chajed authored 4 years ago and Robbert Krebbers committed 4 years ago

When running `iDestruct "H" as (?) "H"`, use the name of the binder in
"H". For example, if "H" has type `∃ y, Φ y`,  we now use `y` as the
name of the variable after freshening. Previously the name was always
the equivalent of running `fresh H`.

The implementation achieves this by forwarding the desired identifier
name through the `IntoExist` typeclass. Identifiers are serialized in
Gallina by using them as the name of a function of type `ident_name :=
unit -> unit`.

Fixes #325.

Also added a tests for the various `iSpecialize` error cases involving
the `[%]` and `[//]` specialization patterns.

Fixes #307.

Notably this support relies on string to identifier conversion, which
works natively using Ltac2 in Coq 8.11+ and with a plugin
(https://github.com/ppedrot/coq-string-ident) in Coq 8.10. To use it,
you must replace intro_patterns.string_to_ident_hook with a real
implementation; see https://gitlab.mpi-sws.org/iris/string-ident for a
working implementation that works with Coq 8.11 (using Ltac2).

The syntax is %H (within a string intro pattern). This is technically
backwards-incompatible, because this was previously supported and parsed
as % and H separately. To restore the old behavior, separate with a
space, eg [% H].