Re: [feature] how to output absolute paths in git diff? => --show-abs-path

[Timothee Cour <timothee.cour2@gmail.com>]

> Wanting such a feature seems sensible

happy to hear that!

> So this seems to work for --no-index, or if it doesn't what situations doesn't it work in?

cases where path arguments are already absolute (as I showed earlier)


> Is this a mistake, or would you only like --show-abs-paths to implicitly supply --src-prefix, but not --dst-prefix? If so, why?

notice I didn't use `--show-abs-paths` in that example; I'm showing
what `git diff` currently outputs (the `could show` meant depending on
your use case; eg when `get_file1` returns an absolute path and
`get_file2` returns a relative one)

> Ah, so it's about supplying both the prefix *and* absolute paths, whereas I see without --no-index we seem to handle this sort of thing just fine:

indeed, without `--no-index` things work just fine as I noted in
https://stackoverflow.com/questions/22698505/how-to-show-full-paths-in-git-diff.
The problem is with `--no-index`
I tried messing around with `--src-prefix` and `--dst-prefix` to
remedy this but as I showed, it can't work currently.

> without --no-index we seem to handle this sort of thing just fine:

you also need `--relative` in case you're not at repo root in your
snippet (that' what I'm using, without `--no-index`)


> This is because the default prefixes are a/ and b/, respectively

that seems buggy:
with default options I get:
--- a/Users/timothee/help0.txt
+++ b/help1.txt

with `--src-prefix=FOO ` and `--dst-prefix=FOO ` I get:
--- FOOUsers/timothee/help0.txt
+++ FOOhelp1.txt

this seems buggy because there's not good option for FOO:
when FOO = /, relative paths become a broken absolute path (/help1.txt)
when FOO = ./, absolute paths become a broken relative path
(./Users/timothee/help0.txt)

I propose instead to show:
with `--src-prefix=FOO ` and `--dst-prefix=FOO ` I get:
--- join(FOO,path1)
+++ join(FOO,path2)

where join(prefix, path) simply appends prefix to path, taking care of
avoiding a double `//` in case prefix ends in / and path starts with
/,

that way, the defauls (with a/, b/) are unchanged and we can have:
with `--src-prefix=` and `--dst-prefix=` (empty FOO):
--- /Users/timothee/help0.txt
+++ help1.txt
=> the paths are not broken

## summary:

* `--show-abs-paths` would be useful
* `--src-prefix=FOO ` and `--dst-prefix=FOO ` could use join(FOO,path)
instead of the currently used join(FOO,path1.removeLeadingSlash)
On Thu, Aug 23, 2018 at 2:42 AM Ævar Arnfjörð Bjarmason
<avarab@gmail.com> wrote:
>
> On Thu, Aug 23, 2018 at 11:16 AM Timothee Cour <thelastmammoth@gmail.com> wrote:
> >
> > This has all the context:
> > https://stackoverflow.com/questions/22698505/how-to-show-full-paths-in-git-diff
>
> It's helpful to copy it anyway, so we can discuss it here:
>
> QUOTE
>
> How do I show full paths in git diff? One can use '--dst-prefix=$PWD'
> and '--src-prefix=$PWD' but this is fragile as it won't work in many
> cases, eg with --no-index, or when running the commond from a
> subdirectory without using --relative=realpath_to_cwd
>
> END QUOTE
>
> Wanting such a feature seems sensible. But I'm unclear on the details.
>
> You say that --{src,dst}-prefix is fragile and doesn't work for
> --no-index. But if I do this:
>
>     (
>     cd /tmp &&
>     echo foo >a &&
>     echo bar >b &&
>     git --no-pager diff --src-prefix=$PWD/ --dst-prefix=$PWD/ a b
>     )
>
> I get this diff:
>
>     diff --git /tmp/a /tmp/b
>     new file mode 100644
>     index 257cc56..5716ca5 100644
>     --- /tmp/a
>     +++ /tmp/b
>     @@ -1 +1 @@
>     -foo
>     +bar
>
> So this seems to work for --no-index, or if it doesn't what situations
> doesn't it work in?
>
> > I'd like `--show-abs-path` to show absolute paths in:
> > git diff --show-abs-path args...
> >
> > eg:
> > git diff --no-index `get_file1` `get_file2`
> > could show:
> > --- a/Users/timothee/temp/ripgrep/help0.txt
> > +++ b/help1.txt
>
> Is this a mistake, or would you only like --show-abs-paths to
> implicitly supply --src-prefix, but not --dst-prefix? If so, why?
>
> > * passing '--dst-prefix=$PWD' and '--src-prefix=$PWD' doesn't help
> > because path arguments could be absolute, so it'll create
> > $PWD/Users/timothee/temp/ripgrep/help0.txt (wrong)
>
> Ah, so it's about supplying both the prefix *and* absolute paths,
> whereas I see without --no-index we seem to handle this sort of thing
> just fine:
>
>     git diff --src-prefix=$PWD/ --dst-prefix=$PWD HEAD~.. $PWD/some-file
>
> > * passing '--dst-prefix=.' will behave weirdly, replacing leading `/`
> > by `.` (seems wrong)
> > diff --git .Users/timothee/temp/ripgrep/help0.txt b/help1.txt
>
> This is because the default prefixes are a/ and b/, respectively, and
> the option allows you to entirely replace them. E.g. imagine needing
> "../some-relative-path/"
>
> > NOTE: I'm invoking the `git diff` command via a more complicated case
> > (with multiple arguments including git diff flags and git diff files),
> > so it's awkward for me to parse which arguments correspond to a file
> > vs a flag (ie prevents easily converting input file arguments to
> > absolute paths), but `git` could do it easily via a flag, eg
> > `--show-abs-path`