When vim-gitgutter is configured to update on `BufEnter`, which is the
default, we only need to update visible buffers on `FocusGained`.
Other buffers will be updated as and when the user enters them.
When opening Vim without editing any file, calling GitGutterDisable
would fail because `s:file` was undefined at that point. The fix breaks
what encapsulation there is, but has the virtue of working.
The sign column automatically appears when there is at least one sign
and disappears when there are none. There's a small gap between
when vim-gitgutter removes its signs and adds new ones; during that gap
the sign column can flicker.
By adding a dummy sign before removing the real signs, we force the sign
column to remain.
Highlight groups for signs:
- renamed highlight groups with `GitGutter` prefix, and following the
naming style of the builtin groups `DiffAdd`, `DiffChange`, etc.
- using `highlight default link` to set default colours for signs.
e.g. the plugin defines `GitGutterAddDefault` as green, and default
(if `g:gitgutter_highlights`) links `GitGutterAdd` to it (which the
user can customise).
Highlight groups for lines:
- added gitgutter-specific highlight groups for line highlighting
(`GitGutterAddLine`, etc) so that this highlighting can be customised
independent of `DiffAdd` et al (which these default link to).
- line highlighting toggling now only changes the linehl attribute.
The `linehl` attribute is toggled in `s:update_line_highlights`,
which separates concerns more clearly. I'm thinking ahead to the
possibility of the sign text being configurable, and thinking it will
be DRYer to keep these things separate. Maybe it's just aesthetic
though.
Bonus: resolved "eugh" ;)
This updates the signs on the current file when you return to GUI vim.
For example, you make some changes in Vim, tab to your shell and commit
them, then tab back to Vim; at this point you want the signs to update
automatically for you.
