Re: Another git question

[Tait <gnu...@t4...>]

Ethan A Merritt via gnuplot-beta <gnu...@li...> said (on 2017/11/17):
> Here's part of the problem I'm having with tracking ChangeLog in git.
> 
> Suppose that a git format-patch file contains a ChangeLog entry that is
> supposed to go at the top of the current ChangeLog file.  Like this:
> 
> diff --git a/ChangeLog b/ChangeLog
> index 9ca7eee..285597c 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -0,0 +1,4 @@
> +2017-11-17  Ethan A Merritt  <merritt@u.washington.edu>
> +
> +	git does not like this diff format
> +
> 
> The entire patch file containing this piece is rejected by "git apply"
> or "git am", apparently because it does not like the syntax "@@ -0,0"
> which diff/patch use to indicate "top of file".
> 
> I can apply the patch manually using "patch" and then run "git commit",
> but this loses the commit message and author information that was in
> the original formatted patch.
> 
> Is there some config option for "git am" and/or "git apply" that tells
> it to accept this syntax in a patch file?
> 
> Note: "patch" will also accept "@@ -1,0" rather than "@@ -0,0" but
> git doesn't like this form either.
> 
> 	Ethan

How was this patch-file generated?

Git refuses to apply a patch with no context, and usually does
not generate one. So in the ChangeLog example, the patch,
whether generated by "git diff" or "git format-patch" would
normally be generated with three context lines, and look
something like:

diff --git a/ChangeLog b/ChangeLog
index 9ca7eee..285597c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2017-11-17  Ethan A Merritt  <merritt@u.washington.edu>
+
+ git does not like this diff format
+
 ===============================================================================
 If you are seeing this you must have obtained a snapshot of gnuplot development
 from the development cvs repository on sourceforge.net.  This is out of date!

You can reduce it down to a single line of context, and the
patch will still apply:

diff --git a/ChangeLog b/ChangeLog
index 9ca7eee..285597c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,1 +1,5 @@
+2017-11-17  Ethan A Merritt  <merritt@u.washington.edu>
+
+ git does not like this diff format
+
 ===============================================================================

But using zero lines of context, as in "@@ -0,0 +1,4 @@", does
not apply. Even generating the patch with "git format-patch -U0"
and applying it verbatim on the same commit it was generated
from, will fail. There is an option to git-apply,
"--unidiff-zero", to force application even with no context, but
it does not appear that this option has been extended to git-am.

If you are adding a new file, then obviously there is no context
to provide. In this case, git uses the special "old" filename of
/dev/null as an indicator that there is no prior context, and
this seems to be required. Example:

diff --git a/ChangeLog b/ChangeLog
new file mode 100644
index 9ca7eee..285597c 100644
--- /dev/null
+++ b/ChangeLog
@@ -0,0 +1,4 @@
+2017-11-17  Ethan A Merritt  <merritt@u.washington.edu>
+
+ git does not like this diff format
+

You'll notice it also adds the "new file mode" above the index
line, but the mode line does not seem to be strictly required
for the patch to apply.