subrepo: add 'cat' support for git subrepos

V2: use 'self._ctx.node()' instead of 'rev' in makefileobj.
As Matt Harbison mentioned, using 'rev' does not make sense,
since we'd be passing a git revision to the top-level
Mercurial repository.

mercurial/help/subrepos.txt

@@ -91,7 +91,7 b' Interaction with Mercurial Commands'
     -S/--subrepos is specified.
 
 :cat: cat currently only handles exact file matches in subrepos.
-    Git and Subversion subrepositories are currently ignored.
+    Subversion subrepositories are currently ignored.
 
 :commit: commit creates a consistent snapshot of the state of the
     entire project and its subrepositories. If any subrepositories

mercurial/subrepo.py

@@ -1577,6 +1577,25 b' class gitsubrepo(abstractsubrepo):'
 
 
     @annotatesubrepoerror
+    def cat(self, match, prefix, **opts):
+        rev = self._state[1]
+        if match.anypats():
+            return 1 #No support for include/exclude yet
+
+        if not match.files():
+            return 1
+
+        for f in match.files():
+            output = self._gitcommand(["show", "%s:%s" % (rev, f)])
+            fp = cmdutil.makefileobj(self._subparent, opts.get('output'),
+                                     self._ctx.node(),
+                                     pathname=os.path.join(prefix, f))
+            fp.write(output)
+            fp.close()
+        return 0
+
+
+    @annotatesubrepoerror
     def status(self, rev2, **opts):
         rev1 = self._state[1]
         if self._gitmissing() or not rev1:

tests/test-subrepo-git.t

@@ -802,4 +802,52 b' revert the subrepository'
   $ hg status --subrepos
   ? s/barfoo
 
+show file at specific revision
+  $ cat > s/foobar << EOF
+  > woop    woop
+  > fooo bar
+  > EOF
+  $ hg commit --subrepos -m "updated foobar"
+  committing subrepository s
+  $ cat > s/foobar << EOF
+  > current foobar
+  > (should not be visible using hg cat)
+  > EOF
+
+  $ hg cat -r . s/foobar
+  woop    woop
+  fooo bar (no-eol)
+  $ hg cat -r "parents(.)" s/foobar > catparents
+
+  $ mkdir -p tmp/s
+
+  $ hg cat -r "parents(.)" --output tmp/%% s/foobar
+  $ diff tmp/% catparents
+
+  $ hg cat -r "parents(.)" --output tmp/%s s/foobar
+  $ diff tmp/foobar catparents
+
+  $ hg cat -r "parents(.)" --output tmp/%d/otherfoobar s/foobar
+  $ diff tmp/s/otherfoobar catparents
+
+  $ hg cat -r "parents(.)" --output tmp/%p s/foobar
+  $ diff tmp/s/foobar catparents
+
+  $ hg cat -r "parents(.)" --output tmp/%H s/foobar
+  $ diff tmp/255ee8cf690ec86e99b1e80147ea93ece117cd9d catparents
+
+  $ hg cat -r "parents(.)" --output tmp/%R s/foobar
+  $ diff tmp/10 catparents
+
+  $ hg cat -r "parents(.)" --output tmp/%h s/foobar
+  $ diff tmp/255ee8cf690e catparents
+
+  $ rm tmp/10
+  $ hg cat -r "parents(.)" --output tmp/%r s/foobar
+  $ diff tmp/10 catparents
+
+  $ mkdir tmp/tc
+  $ hg cat -r "parents(.)" --output tmp/%b/foobar s/foobar
+  $ diff tmp/tc/foobar catparents
+
   $ cd ..