Contrary to the "diff" utility, "svn diff" outputs 2 chunks instead
of 1 when there are 6 consecutive unmodified lines.

To reproduce the bug, create a file with "seq 14" and commit it.
Then modify the lines 4 and 11 (e.g. add a "b" character). I get
with Subversion's internal diff:

$ svn diff
Index: f
===================================================================
--- f   (revision 1)
+++ f   (working copy)
@@ -1,7 +1,7 @@
 1
 2
 3
-4
+4b
 5
 6
 7
@@ -8,7 +8,7 @@
 8
 9
 10
-11
+11b
 12
 13
 14

while the "diff" command gives:

$ svn --diff-cmd diff diff
Index: f
===================================================================
--- f   (revision 1)
+++ f   (working copy)
@@ -1,14 +1,14 @@
 1
 2
 3
-4
+4b
 5
 6
 7
 8
 9
 10
-11
+11b
 12
 13
 14

Control: severity -1 minor

I don't think svn claims to produce identical diffs to that of the diff
command, so this is at most a minor issue, if not wishlist.

Also, the diffs are functionally equivalent, so I'm not sure how this
matters other than the diffs being different.

Cheers,

Well, actually, what initially confused me with the "svn diff" output
is that I thought that two output chunks were necessarily disjoint
and non adjacent[*]. So, it seemed to me that there was a problem
with my file, until I noticed that the chunks output by "svn diff"
were adjacent. I hope that my bug report is more clear now.

[*] AFAIK, this is always the case with GNU diff, and this is why
I thought that this was a general rule for the unified diff format.

Now, what's interesting is what POSIX says:

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html

  "If -U n is specified, the output shall contain no more than
  n consecutive unaffected lines; and if the output contains an
  affected line and this line is adjacent to up to n consecutive
  unaffected lines in the corresponding file, the output shall
  contain these unaffected lines. -u shall act like -U3."

So, it appears that "svn diff" follows POSIX here (but it doesn't when
there are exactly 5 consecutive unaffected lines). And GNU diff more
generally doesn't follow POSIX, even though this page later says that
the -u and -U options come from GNU diff!

At least there is a lack of specification for "svn diff". But I think
that a rule requiring disjoint and non adjacent chunks is intuitively
better for a human reader.