Try harder to detect an existing checkout before 'fetch'ing.

fetch.py

Index: fetch.py
diff --git a/fetch.py b/fetch.py
index 04be95fa48ea0d095692a321c0e6b14ec5fedb57..d2fbf7382c4e606908908f7e8cf314c80e91347a 100755
--- a/fetch.py
+++ b/fetch.py
@@ -63,7 +63,7 @@ class Checkout(object):
     print 'Running: %s' % (' '.join(pipes.quote(x) for x in cmd))
     if self.options.dry_run:
       return 0
-    return subprocess.check_call(cmd, **kwargs)
+    return subprocess.check_output(cmd, **kwargs)
 
 
 class GclientCheckout(Checkout):
@@ -121,6 +121,13 @@ class GclientGitCheckout(GclientCheckout, GitCheckout):
     return gclient_spec
 
   def exists(self):

[agable, 2015/06/10 17:54:28]

Rather than doing this, I would define exists() on the top-level GclientCheckout
and run self.run_gclient('root') to see if it finds a .gclient file. wdyt?

[Michael Moss, 2015/06/10 18:10:47]

Yeah, I wasn't sure how strict we wanted to be, so I was just trying to exclude
"redundant" checkouts, as opposed to "any checkout within any checkout" (though
I don't know why anybody would want to do that). I'm not opposed to the latter
if you think that's better.

[agable, 2015/06/10 18:22:16]

We don't have any GclientSVN-based fetch recipes anymore (and should probably
delete that code because screw svn). So doing it here is probably fine. But the
purist in me really wants to make sure we cover all the cases. And since there's
a base class that understands gclient anyway...

Not necessary. But I think it would be way more elegant and less likely to
surprise someone later down the line.

+    solution_urls = [s.get('url') for s in self.spec.get('solutions', [])]
+    try:
+      current_remote = self.run_git('config', '--get', 'remote.origin.url')
+      if current_remote.strip() in solution_urls:
+        return True
+    except subprocess.CalledProcessError:
+      pass
     return os.path.exists(os.path.join(os.getcwd(), self.root))
 
   def init(self):
@@ -315,8 +322,9 @@ def run(options, spec, root):
   except KeyError:
     return 1
   if checkout.exists():
-    print 'You appear to already have a checkout. "fetch" is used only'
-    print 'to get new checkouts. Use "gclient sync" to update the checkout.'
+    print 'Your current directory appears to already contain, or be part of, '
+    print 'a checkout. "fetch" is used only to get new checkouts. Use '
+    print '"gclient sync" to update existing checkouts.'
     print
     print 'Fetch also does not yet deal with partial checkouts, so if fetch'
     print 'failed, delete the checkout and start over (crbug.com/230691).'