export: add %m to file format string (first line of the commit message)

$ hg commit -m "Initial commit"
$ hg export -o %m.patch tip          #It creates Initial_commit.patch file.

mercurial/cmdutil.py

@@ -109,12 +109,13 b' def loglimit(opts):'
         limit = None
     return limit
 
-def makefilename(repo, pat, node,
+def makefilename(repo, pat, node, desc=None,
                   total=None, seqno=None, revwidth=None, pathname=None):
     node_expander = {
         'H': lambda: hex(node),
         'R': lambda: str(repo.changelog.rev(node)),
         'h': lambda: short(node),
+        'm': lambda: re.sub('[^\w]', '_', str(desc))
         }
     expander = {
         '%': lambda: '%',
@@ -154,7 +155,7 b' def makefilename(repo, pat, node,'
         raise util.Abort(_("invalid format spec '%%%s' in output filename") %
                          inst.args[0])
 
-def makefileobj(repo, pat, node=None, total=None,
+def makefileobj(repo, pat, node=None, desc=None, total=None,
                 seqno=None, revwidth=None, mode='wb', pathname=None):
 
     writable = mode not in ('r', 'rb')
@@ -181,7 +182,7 b' def makefileobj(repo, pat, node=None, to'
         return pat
     if util.safehasattr(pat, 'read') and 'r' in mode:
         return pat
-    return open(makefilename(repo, pat, node, total, seqno, revwidth,
+    return open(makefilename(repo, pat, node, desc, total, seqno, revwidth,
                               pathname),
                 mode)
 
@@ -516,8 +517,10 b" def export(repo, revs, template='hg-%h.p"
 
         shouldclose = False
         if not fp:
-            fp = makefileobj(repo, template, node, total=total, seqno=seqno,
-                             revwidth=revwidth, mode='ab')
+            desc_lines = ctx.description().rstrip().split('\n')
+            desc = desc_lines[0]    #Commit always has a first line.
+            fp = makefileobj(repo, template, node, desc=desc, total=total,
+                             seqno=seqno, revwidth=revwidth, mode='ab')
             if fp != template:
                 shouldclose = True
         if fp != sys.stdout and util.safehasattr(fp, 'name'):

mercurial/commands.py

@@ -2229,6 +2229,7 b' def export(ui, repo, *changesets, **opts'
     :``%R``: changeset revision number
     :``%b``: basename of the exporting repository
     :``%h``: short-form changeset hash (12 hexadecimal digits)
+    :``%m``: first line of the commit message (only alphanumeric characters)
     :``%n``: zero-padded sequence number, starting at 1
     :``%r``: zero-padded changeset revision number
 

tests/test-export.t

@@ -7,7 +7,7 b''
   >    hg ci -m "foo-$i"
   > done
 
-  $ for out in "%nof%N" "%%%H" "%b-%R" "%h" "%r"; do
+  $ for out in "%nof%N" "%%%H" "%b-%R" "%h" "%r" "%m"; do
   >    echo
   >    echo "# foo-$out.patch"
   >    hg export -v -o "foo-$out.patch" 2:tip
@@ -77,6 +77,19 b''
   foo-09.patch
   foo-10.patch
   foo-11.patch
+  
+  # foo-%m.patch
+  exporting patches:
+  foo-foo_2.patch
+  foo-foo_3.patch
+  foo-foo_4.patch
+  foo-foo_5.patch
+  foo-foo_6.patch
+  foo-foo_7.patch
+  foo-foo_8.patch
+  foo-foo_9.patch
+  foo-foo_10.patch
+  foo-foo_11.patch
 
 Exporting 4 changesets to a file:
 
@@ -108,3 +121,11 b' Exporting revision -2 to a file:'
    foo-9
   +foo-10
 
+Checking if only alphanumeric characters are used in the file name (%m option):
+
+  $ echo "line" >> foo
+  $ hg commit -m " !\"#$%&(,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_\`abcdefghijklmnopqrstuvwxyz{|}~" 
+  $ hg export -v -o %m.patch tip
+  exporting patch:
+  ____________0123456789_______ABCDEFGHIJKLMNOPQRSTUVWXYZ______abcdefghijklmnopqrstuvwxyz____.patch
+