sparse: don't crash in non-sparse repositories

Summary:
Update the workingfilectxdata() to check that this is actually a sparse
repository before trying to call repo.sparsematch()

Test Plan: Update the test to confirm that "hg diff" works instead of crashes now.

Reviewers: #fbhgext, mbthomas

Reviewed By: #fbhgext, mbthomas

Differential Revision: https://phab.mercurial-scm.org/D1023

hgext3rd/sparse.py

@@ -348,6 +348,8 @@ def _setupdiff(ui):
     # wrap workingfilectx's data function to return the data for files
     # outside the sparse checkout by fetching from the working copy parent.
     def workingfilectxdata(orig, self):
+        if not util.safehasattr(self.repo(), 'sparsematch'):
+            return orig(self)
         sparsematch = self.repo().sparsematch()
         if sparsematch(self._path):
             return orig(self)

tests/test-sparse-notsparse.t

@@ -32,6 +32,10 @@ Now create a shared working copy that is not sparse.
 Make sure "hg diff" works in the non-sparse working directory.
 
   $ echo z >> file1
-  $ hg diff |& grep -E 'Unknown exception|AttributeError'
-  ** Unknown exception encountered with possibly-broken third-party extension sparse
-  AttributeError: 'localrepository' object has no attribute 'sparsematch'
+  $ hg diff
+  diff -r 1f02e070b36e file1
+  --- a/file1	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/file1	Thu Jan 01 00:00:00 1970 +0000
+  @@ -1,1 +1,2 @@
+   a
+  +z