This style for RopeGraphemes is identical to Ropey's Chars and Bytes
iterators. Being able to move the iterator types like cursors over the
bytes/chars/graphemes is useful in some cases. For example see
`helix_core::movement::<Chars as CharHelpers>::range_to_target`.
This change also adds `RopeSliceExt::graphemes_at` for flexibility.
`graphemes` and `graphemes_rev` are now implemented in terms of
`graphemes_at` and `RopeGraphemes::reversed`.
These functions mirror those in `helix_core::graphemes` but operate
directly on byte indices rather than character indices. These are meant
to be used as we transition to Ropey v2 and always use byte indices.
These functions are the equivalent of 23b424a46 for grapheme clusters.
In order to add the `is_grapheme_boundary` function we also need to
query whether a byte index lies on a character boundary, so this change
also adds `is_char_boundary`.
The new `RopeSliceExt::ceil_char_boundary` from the parent commits can
be used to implement `RopeSliceExt::byte_to_next_char` when used with
`RopeSlice::byte_to_char`. That function had only one caller and that
caller will eventually disappear when we switch to Ropey v2 and drop
character indexing, so we can drop `byte_to_next_char` now and replace
its caller with `byte_to_char` plus `ceil_char_boundary`.
This change keeps the unit tests for `byte_to_next_char` and checks them
against a polyfill of `byte_to_char` plus `ceil_char_boundary` to ensure
that `byte_to_next_char`'s intended behavior is not changed.
These functions mimic `str::floor_char_boundary` and
`str::floor_char_boundary` (currently unstable under
`round_char_boundary`). They're useful for correcting a byte index
which may not lie on a character boundary. For example you might limit
a search within a slice to some fixed number of bytes. The fixed number
might not lie on a boundary though so it needs to be corrected to
either the earlier (floor) or later (ceil) boundary.
Michael Davis
Rolo
rhogenson
Pascal Kuthe
Gabriel Dinner-David
Pascal Kuthe