Re: [PATCH] Teach 'git-apply --whitespace=strip' to remove empty lines at the end of file

"Marco Costalba" [off-list ref] writes:

On 5/21/07, Junio C Hamano [off-list ref] wrote:

quoted

Junio C Hamano [off-list ref] writes:


We somehow end up removing one LF too many, like this:

    diff --git a/contrib/emacs/.gitignore b/contrib/emacs/.gitignore
    index c531d98..016d3b1 100644
    --- a/contrib/emacs/.gitignore
    +++ b/contrib/emacs/.gitignore
    @@ -1 +1 @@
    -*.elc
    +*.elc
    \ No newline at end of file

I also had that, but after adding

+
+               if (empty < trailing_added_lines)
+                       empty--;
+

everything worked correctly. I made again the same test myself
without problems.

I really don't understand how could be broken.

Hmmm.  Puzzled.

Let's say that the patch is to create a file that has a single
line, like this:

diff --git a/contrib/emacs/.gitignore b/contrib/emacs/.gitignore
new file mode 100644
index 0000000..c531d98
--- /dev/null
+++ b/contrib/emacs/.gitignore

@@ -0,0 +1 @@
+*.elc

The function "apply_one_fragment" gets two lines ('@' and '+').

We come to "while (size > 0)" loop.  During the first round,
'first' is '@' and the line is ignored.  In the second round,
'first' is '+', so apply_line appends the contents to 'new'
buffer, while we count trailing_added_lines.

End result is

 - newsize = 6, new has "*.elc\n";
 - oldsize = 0, and old has "";
 - trailing_added_lines = 1;

when we get to the "empty" counting code.

Then you count empty up to trailing_added_lines.  When we get to
the "if (empty < trailing_added_lines)" code, empty is 1.  You
do not decrement this, and take that number in
trailing_added_lines, to be used to strip the trailing run of
newlines in the for (;;) loop later.  That's how you can lose
the last newline that is not on a blank line.