patchTeach 'git-apply --whitespace=strip' to remove empty lines at the end of file

diff --git a/builtin-apply.c b/builtin-apply.c
index 0399743..a96f669 100644
--- a/builtin-apply.c
+++ b/builtin-apply.c
@@ -1671,6 +1671,7 @@ static int apply_one_fragment(struct buffer_desc *desc,
 	char *new = xmalloc(size);
 	const char *oldlines, *newlines;
 	int oldsize = 0, newsize = 0;
+	int trailing_added_lines = 0;
 	unsigned long leading, trailing;
 	int pos, lines;

@@ -1699,6 +1700,15 @@ static int apply_one_fragment(struct buffer_desc *desc,
 			else if (first == '+')
 				first = '-';
 		}
+		/*
+		 * Only fragments that add lines at the bottom
+		 * of a file end with a list of '+' lines
+		*/
+		if (first == '+')
+			trailing_added_lines++;
+		else
+			trailing_added_lines = 0;
+
 		switch (first) {
 		case '\n':
 			/* Newer GNU diff, empty context line */
@@ -1738,6 +1748,18 @@ static int apply_one_fragment(struct buffer_desc *desc,
 		newsize--;
 	}

+	if (new_whitespace == strip_whitespace) {
+		/* Any added empty lines is already cleaned-up here
+		 * becuase of 'strip_whitespace' flag, so just count '\n'
+		*/
+		int empty = 0;
+		while (   empty < trailing_added_lines
+		       && newsize - empty - 2 > 0
+		       && new[newsize - empty - 2] == '\n')
+			empty++;
+
+		newsize -= empty;
+	}
 	oldlines = old;
 	newlines = new;
 	leading = frag->leading;

diff --git a/AAA b/AAA
index d68dd40..8410b89 100644
--- a/AAA
+++ b/AAA
@@ -2,0 +3,3 @@ b
+
+
+

Because we had the same mistake in our earlier code as you made
in this patch, which assumed that a hunk that ends with '+' only
apply at the end (and we still assume that by default), if you
apply this with patch git-apply without --unidiff-zero option,
you get an error.  If you use the option this patch can be
applied correctly.

$ git checkout -- AAA ;# to go back to the original a/b/c/d
$ git apply --unidiff-zero P.diff

Now, with --unidiff-zero option, I think your patch will mistake
that this hunk adds _trailing_ blank lines, because it does not
see anything that comes after the '+'.

        I think it should notice that it adds three trailing
        blank lines and should reduce "new" to zero lines, but
        somehow it does not seem to do so.  You start with
        newsize == 3 and do not allow (newsize-empty) to go
        below 2, so you would get only 1 in empty, not 3, and
        end up reducing this hunk by only one line.

        Which may or may not be a bug, but that is besides the
        point.

The point is that this hunk does not apply to the end of the
file, and I do not think you should even be attempting to reduce
"new" at all.

But the code to determine where in the dest buffer the hunk
applies to exists way after the point you patched (inside of the
for(;;) loop, where we have memmove and memcpy).  The memmove is
to move away the later part of the file to make room if "new" is
larger than "old" (if the hunk deletes more than it adds, the
memmove would move the remainder up, otherwise down), and I
think that should be the place you would first decide if you are
applying at the end, and reduce "new" only if that is the case.

Am I misreading your patch?

diff --git a/builtin-apply.c b/builtin-apply.c
index 0399743..6032f78 100644
--- a/builtin-apply.c
+++ b/builtin-apply.c
@@ -1671,6 +1671,7 @@ static int apply_one_fragment(struct buffer_desc *desc,
 	char *new = xmalloc(size);
 	const char *oldlines, *newlines;
 	int oldsize = 0, newsize = 0;
+	int trailing_added_lines = 0;
 	unsigned long leading, trailing;
 	int pos, lines;

@@ -1699,6 +1700,17 @@ static int apply_one_fragment(struct buffer_desc *desc,
 			else if (first == '+')
 				first = '-';
 		}
+		/*
+		 * Count lines added at the end of the file.
+		 * This is not enough to get things right in case of
+		 * patches generated with --unified=0, but it's a
+		 * useful upper bound.
+		*/
+		if (first == '+')
+			trailing_added_lines++;
+		else
+			trailing_added_lines = 0;
+
 		switch (first) {
 		case '\n':
 			/* Newer GNU diff, empty context line */
@@ -1738,6 +1750,24 @@ static int apply_one_fragment(struct buffer_desc *desc,
 		newsize--;
 	}

+	if (new_whitespace == strip_whitespace) {
+		/* Any added empty lines is already cleaned-up here
+		 * becuase of 'strip_whitespace' flag, so just count '\n'
+		*/
+		int empty = 0;
+		while (   empty < trailing_added_lines
+		       && newsize - empty > 0
+		       && new[newsize - empty - 1] == '\n')
+			empty++;
+
+		if (empty < trailing_added_lines)
+			empty--;
+
+		/* these are the empty lines added at
+		 * the end of the file, modulo u0 patches.
+		 */
+		trailing_added_lines = empty;
+	}
 	oldlines = old;
 	newlines = new;
 	leading = frag->leading;
@@ -1770,6 +1800,10 @@ static int apply_one_fragment(struct buffer_desc *desc,
 		if (match_beginning && offset)
 			offset = -1;
 		if (offset >= 0) {
+
+			if (desc->size - oldsize - offset == 0) /* end of file? */
+				newsize -= trailing_added_lines;
+
 			int diff = newsize - oldsize;
 			unsigned long size = desc->size + diff;
 			unsigned long alloc = desc->alloc;

diff --git a/builtin-apply.c b/builtin-apply.c
index ac7c824..e717898 100644
--- a/builtin-apply.c
+++ b/builtin-apply.c
@@ -1671,7 +1671,7 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag, i
 	char *new = xmalloc(size);
 	const char *oldlines, *newlines;
 	int oldsize = 0, newsize = 0;
-	int trailing_added_lines = 0;
+	int new_blank_lines_at_end = 0;
 	unsigned long leading, trailing;
 	int pos, lines;
 
@@ -1679,6 +1679,7 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag, i
 		char first;
 		int len = linelen(patch, size);
 		int plen;
+		int added_blank_line = 0;
 
 		if (!len)
 			break;
@@ -1700,16 +1701,6 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag, i
 			else if (first == '+')
 				first = '-';
 		}
-		/*
-		 * Count lines added at the end of the file.
-		 * This is not enough to get things right in case of
-		 * patches generated with --unified=0, but it's a
-		 * useful upper bound.
-		*/
-		if (first == '+')
-			trailing_added_lines++;
-		else
-			trailing_added_lines = 0;
 
 		switch (first) {
 		case '\n':
@@ -1728,9 +1719,14 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag, i
 				break;
 		/* Fall-through for ' ' */
 		case '+':
-			if (first != '+' || !no_add)
-				newsize += apply_line(new + newsize, patch,
-						      plen);
+			if (first != '+' || !no_add) {
+				int added = apply_line(new + newsize, patch,
+						       plen);
+				newsize += added;
+				if (first == '+' &&
+				    added == 1 && new[newsize-1] == '\n')
+					added_blank_line = 1;
+			}
 			break;
 		case '@': case '\\':
 			/* Ignore it, we already handled it */
@@ -1740,6 +1736,10 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag, i
 				error("invalid start of line: '%c'", first);
 			return -1;
 		}
+		if (added_blank_line)
+			new_blank_lines_at_end++;
+		else
+			new_blank_lines_at_end = 0;
 		patch += len;
 		size -= len;
 	}
@@ -1750,24 +1750,6 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag, i
 		newsize--;
 	}
 
-	if (new_whitespace == strip_whitespace) {
-		/* Any added empty lines is already cleaned-up here
-		 * becuase of 'strip_whitespace' flag, so just count '\n'
-		*/
-		int empty = 0;
-		while (   empty < trailing_added_lines
-		       && newsize - empty > 0
-		       && new[newsize - empty - 1] == '\n')
-			empty++;
-
-		if (empty < trailing_added_lines)
-			empty--;
-
-		/* these are the empty lines added at
-		 * the end of the file, modulo u0 patches.
-		 */
-		trailing_added_lines = empty;
-	}
 	oldlines = old;
 	newlines = new;
 	leading = frag->leading;
@@ -1805,7 +1787,7 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag, i
 
 			if (new_whitespace == strip_whitespace &&
 			    (desc->size - oldsize - offset == 0)) /* end of file? */
-				newsize -= trailing_added_lines;
+				newsize -= new_blank_lines_at_end;
 
 			diff = newsize - oldsize;
 			size = desc->size + diff;

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.