mdiff/patch: fix bad hunk handling for unified diffs with zero context Prior to this patch "hg diff -U0", i.e., zero lines of context, would output hunk headers with a start line one greater than what GNU patch and git output. Guido van Rossum documents the unified diff format[1] as having a start line value "one lower than one would expect" for zero length hunks. Comparing the behaviour of the three systems prior to this patch in transforming c1 c3 to c1 c2 c3 - GNU "diff -U0" reports the hunk as "@@ -1,0 +2 @@" - "git diff -U0" reports the hunk as "@@ -1,0 +2 @@" - "hg diff -U0" reports the hunk as "@@ -2,0 +2,1 @@" After this patch, "hg diff -U0" reports "@@ -1,0 +2,1 @@". Since "hg export --config diff.unified=0" outputs zero-context unified diffs, "hg import" has also been updated to account for start lines one less than expected for zero length hunk ranges. [1]: http://www.artima.com/weblogs/viewpost.jsp?thread=164293

--- a/mercurial/mdiff.py	Tue Nov 08 17:08:58 2011 +0100
+++ b/mercurial/mdiff.py	Wed Nov 09 16:55:59 2011 -0800
@@ -180,8 +180,14 @@
             # the file more than once.
             lastfunc[0] = astart
 
-        yield "@@ -%d,%d +%d,%d @@%s\n" % (astart + 1, alen,
-                                           bstart + 1, blen, func)
+        # zero-length hunk ranges report their start line as one less
+        if alen:
+            astart += 1
+        if blen:
+            bstart += 1
+
+        yield "@@ -%d,%d +%d,%d @@%s\n" % (astart, alen,
+                                           bstart, blen, func)
         for x in delta:
             yield x
         for x in xrange(a2, aend):