The only reason the realtime diff used `diff` instead of `git-diff`
previously was that I couldn't figure out how to do it in a way that
worked on Windows as well as Unix.
Previously vim-gitgutter generated context-free patches and applied
those to the index. However when staging a hunk situated after any
deleted lines, the line numbers on the patch were out by the number
of lines deleted, and without any context git would apply the patch
to the wrong part of the file in the index.
This commit ensure patches are generated with 1 line of context,
allowing git to adjust the line numbers appropriately and apply the
patch to the right location.
More lines of context would help git more to adjust line numbers; but
the more context we have the more we group together hunks we would
like to treat separately.
Before this commit some Windows users saw the command prompt pop
up briefly, and/or the taskbar flicker, every time the plugin ran.
Now the plugin will use xolox's vim-shell and vim-misc, if they are
available and we are on Windows, to execute external commands. Xolox's
clever plugins avoid the command prompt popup and taskbar flicker.
Windows users with those plugins installed can opt out by setting a
variable in their vimrc.
Many thanks to @suxpert for the initial code.
Note that line highlighting requires signs to be placed (because the
line highlight is simply an attribute of a sign). If the user doesn't
want to see signs in the sign column, but does want line highlighting,
then we make the signs in the sign column invisible.
If neither the signs in the sign column nor the line highlights are
needed (presumably the user just looks at the hunks stats) then we can
remove all signs, at which point Vim removes the sign column...unless
the "sign column always" option is set.
Since we start all external commands by cd'ing to the current file's
directory, we can use the file's name instead of its full path.
The exception is `git show :FILE` where we must use a path relative to
the repo root for maximum git compatibility. It turns out `git
rev-parse` takes a `--show-prefix` argument which makes our relative
path calculation far simpler.
Minimising files paths has these benefits:
- Easier to inspect the generated commands.
- Less opportunity for escaping problems.
- Eliminates possible mismatches betwen absolute paths generated by git
and absolute paths generated by Vim (crops up with msys/msys2 on
Windows).
Thanks to @suxpert for helping with this.
