patch/diff: use a separate function to write the first line of a file diff

mercurial/mdiff.py

@@ -66,6 +66,19 b' def wsclean(opts, text):'
         text = re.sub('\n+', '', text)
     return text
 
+def diffline(revs, a, b, opts):
+    parts = ['diff']
+    if opts.git:
+        parts.append('--git')
+    if revs and not opts.git:
+        parts.append(' '.join(["-r %s" % rev for rev in revs]))
+    if opts.git:
+        parts.append('a/%s' % a)
+        parts.append('b/%s' % b)
+    else:
+        parts.append(a)
+    return ' '.join(parts) + '\n'
+    
 def unidiff(a, ad, b, bd, fn1, fn2, r=None, opts=defaultopts):
     def datetag(date, addtab=True):
         if not opts.git and not opts.nodates:
@@ -113,8 +126,7 b' def unidiff(a, ad, b, bd, fn1, fn2, r=No'
             l[ln] += "\n\ No newline at end of file\n"
 
     if r:
-        l.insert(0, "diff %s %s\n" %
-                    (' '.join(["-r %s" % rev for rev in r]), fn1))
+        l.insert(0, diffline(r, fn1, fn2, opts))
 
     return "".join(l)
 

mercurial/patch.py

@@ -1266,7 +1266,7 b' def diff(repo, node1=None, node2=None, m'
                 if util.binary(to) or util.binary(tn):
                     dodiff = 'binary'
             r = None
-            header.insert(0, 'diff --git a/%s b/%s\n' % (a, b))
+            header.insert(0, mdiff.diffline(r, a, b, opts))
         if dodiff:
             if dodiff == 'binary':
                 text = b85diff(to, tn)