Incorrect unified diff when run with "--find-copies-harder"

Incorrect unified diff when run with "--find-copies-harder"

[Daniel Penkin]

Hello,

I believe I found a bug in how Git represents a diff when invoked with
"--find-copies-harder" parameter.
Specifically, the unified diff header of a hunk contains an extra
piece of text which appears to be a line from the context (i.e.
unchanged line), something like this:

    > git diff --find-copies-harder d00ca3f 20fb313
    diff --git a/test.txt b/copy.txt
    similarity index 81%
    copy from test.txt
    copy to copy.txt
    index 734156d..43a3f9d 100644
    --- a/test.txt
    +++ b/copy.txt
    @@ -2,6 +2,7 @@ line 1
     line 2
     line 3
     line 4
    +added line
     line 5
     line 6
     line 7

Note "line 1" after the standard unified diff header.

I prepared a sample repository with a minimal file I can reproduce
this problem with:
https://bitbucket.org/dpenkin/find-copies-harder-bug

I'm running Git 2.18.0 on a macOS, but I also tried with Git 2.15.0
and 2.8.6 running on Alpine Linux and was able to reproduce the same
problem.

Please advise whether this is expected output or is indeed a bug.

Thank you.

Kind regards,
Daniil Penkin

Re: Incorrect unified diff when run with "--find-copies-harder"

[Andrei Rybak]

On 2018-06-24 12:36, Daniel Penkin wrote:
> Hello,
> 

Hi,

> I believe I found a bug in how Git represents a diff when invoked with
> "--find-copies-harder" parameter.
> Specifically, the unified diff header of a hunk contains an extra
> piece of text which appears to be a line from the context (i.e.
> unchanged line), something like this:
> 
>     > git diff --find-copies-harder d00ca3f 20fb313
>     diff --git a/test.txt b/copy.txt
>     similarity index 81%
>     copy from test.txt
>     copy to copy.txt
>     index 734156d..43a3f9d 100644
>     --- a/test.txt
>     +++ b/copy.txt
>     @@ -2,6 +2,7 @@ line 1
>      line 2
>      line 3
>      line 4
>     +added line
>      line 5
>      line 6
>      line 7
> 
> Note "line 1" after the standard unified diff header.
> 

This text after @@ is usually a function name in a programming language or
some other relevant part of hunk context, to help user navigate the diff more
easily.  What you are getting is the default version of it, as it is just
comparing txt files.  You can read more about it in the documentation of 
gitattributes:

https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header

> I prepared a sample repository with a minimal file I can reproduce
> this problem with:
> https://bitbucket.org/dpenkin/find-copies-harder-bug
> 
> I'm running Git 2.18.0 on a macOS, but I also tried with Git 2.15.0
> and 2.8.6 running on Alpine Linux and was able to reproduce the same
> problem.
> 
> Please advise whether this is expected output or is indeed a bug.
> 

This is expected output.

> Thank you.
> 
> Kind regards,
> Daniil Penkin
> 

--
Best regards, Andrei R.

Re: Incorrect unified diff when run with "--find-copies-harder"

[Daniel Penkin]

Hi Andrei,

Thanks for the prompt reply.

I'm sorry for the false alarm, I should've investigated this more
thoroughly before submitting a bug.
Now I see I get that context hint in many diffs, I was confused by
many simple file diffs I was working with recently which didn't have
it.

Thank you for your time and help.

Kind regards,
Daniil Penkin

вс, 24 июн. 2018 г. в 23:33, Andrei Rybak <rybak.a.v@gmail.com>:
>
> On 2018-06-24 12:36, Daniel Penkin wrote:
> > Hello,
> >
>
> Hi,
>
> > I believe I found a bug in how Git represents a diff when invoked with
> > "--find-copies-harder" parameter.
> > Specifically, the unified diff header of a hunk contains an extra
> > piece of text which appears to be a line from the context (i.e.
> > unchanged line), something like this:
> >
> >     > git diff --find-copies-harder d00ca3f 20fb313
> >     diff --git a/test.txt b/copy.txt
> >     similarity index 81%
> >     copy from test.txt
> >     copy to copy.txt
> >     index 734156d..43a3f9d 100644
> >     --- a/test.txt
> >     +++ b/copy.txt
> >     @@ -2,6 +2,7 @@ line 1
> >      line 2
> >      line 3
> >      line 4
> >     +added line
> >      line 5
> >      line 6
> >      line 7
> >
> > Note "line 1" after the standard unified diff header.
> >
>
> This text after @@ is usually a function name in a programming language or
> some other relevant part of hunk context, to help user navigate the diff more
> easily.  What you are getting is the default version of it, as it is just
> comparing txt files.  You can read more about it in the documentation of
> gitattributes:
>
> https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header
>
> > I prepared a sample repository with a minimal file I can reproduce
> > this problem with:
> > https://bitbucket.org/dpenkin/find-copies-harder-bug
> >
> > I'm running Git 2.18.0 on a macOS, but I also tried with Git 2.15.0
> > and 2.8.6 running on Alpine Linux and was able to reproduce the same
> > problem.
> >
> > Please advise whether this is expected output or is indeed a bug.
> >
>
> This is expected output.
>
> > Thank you.
> >
> > Kind regards,
> > Daniil Penkin
> >
>
> --
> Best regards, Andrei R.