--- a/hgext/sparse.py	Thu Jul 06 12:20:53 2017 -0700
+++ b/hgext/sparse.py	Thu Jul 06 12:24:55 2017 -0700
@@ -510,14 +510,6 @@
 
             return result
 
-        def writesparseconfig(self, include, exclude, profiles):
-            raw = '%s[include]\n%s\n[exclude]\n%s\n' % (
-                ''.join(['%%include %s\n' % p for p in sorted(profiles)]),
-                '\n'.join(sorted(include)),
-                '\n'.join(sorted(exclude)))
-            self.vfs.write("sparse", raw)
-            sparse.invalidatesignaturecache(self)
-
         def addtemporaryincludes(self, files):
             includes = self.gettemporaryincludes()
             for file in files:
@@ -722,7 +714,8 @@
                 newinclude.difference_update(pats)
                 newexclude.difference_update(pats)
 
-            repo.writesparseconfig(newinclude, newexclude, newprofiles)
+            sparse.writeconfig(repo, newinclude, newexclude, newprofiles)
+
             fcounts = map(
                 len, _refresh(ui, repo, oldstatus, oldsparsematch, force))
 
@@ -735,7 +728,7 @@
             _verbose_output(
                 ui, opts, profilecount, includecount, excludecount, *fcounts)
         except Exception:
-            repo.writesparseconfig(oldinclude, oldexclude, oldprofiles)
+            sparse.writeconfig(repo, oldinclude, oldexclude, oldprofiles)
             raise
     finally:
         wlock.release()
@@ -784,13 +777,13 @@
 
             oldstatus = repo.status()
             oldsparsematch = repo.sparsematch()
-            repo.writesparseconfig(includes, excludes, profiles)
+            sparse.writeconfig(repo, includes, excludes, profiles)
 
             try:
                 fcounts = map(
                     len, _refresh(ui, repo, oldstatus, oldsparsematch, force))
             except Exception:
-                repo.writesparseconfig(oincludes, oexcludes, oprofiles)
+                sparse.writeconfig(repo, oincludes, oexcludes, oprofiles)
                 raise
 
         _verbose_output(ui, opts, profilecount, includecount, excludecount,
@@ -804,7 +797,7 @@
         if includes or excludes:
             oldstatus = repo.status()
             oldsparsematch = repo.sparsematch()
-            repo.writesparseconfig(set(), set(), profiles)
+            sparse.writeconfig(repo, set(), set(), profiles)
             _refresh(ui, repo, oldstatus, oldsparsematch, force)
 
 def _refresh(ui, repo, origstatus, origsparsematch, force):

--- a/mercurial/sparse.py	Thu Jul 06 12:20:53 2017 -0700
+++ b/mercurial/sparse.py	Thu Jul 06 12:24:55 2017 -0700
@@ -129,3 +129,23 @@
 
 def invalidatesignaturecache(repo):
     repo._sparsesignaturecache.clear()
+
+def writeconfig(repo, includes, excludes, profiles):
+    """Write the sparse config file given a sparse configuration."""
+    with repo.vfs('sparse', 'wb') as fh:
+        for p in sorted(profiles):
+            fh.write('%%include %s\n' % p)
+
+        if includes:
+            fh.write('[include]\n')
+            for i in sorted(includes):
+                fh.write(i)
+                fh.write('\n')
+
+        if excludes:
+            fh.write('[exclude]\n')
+            for e in sorted(excludes):
+                fh.write(e)
+                fh.write('\n')
+
+    invalidatesignaturecache(repo)

--- a/tests/test-sparse.t	Thu Jul 06 12:20:53 2017 -0700
+++ b/tests/test-sparse.t	Thu Jul 06 12:24:55 2017 -0700
@@ -63,8 +63,6 @@
   $ hg debugsparse
   [include]
   show*
-  [exclude]
-  
   
 Verify update only writes included files
 
@@ -150,8 +148,6 @@
   [1]
 
   $ hg debugsparse
-  [include]
-  
   [exclude]
   hide*
   
@@ -187,8 +183,6 @@
   use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
   [1]
   $ hg debugsparse
-  [include]
-  
   [exclude]
   hide*
   
@@ -199,8 +193,6 @@
   cleaned up 1 temporarily added file(s) from the sparse checkout
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg debugsparse
-  [include]
-  
   [exclude]
   hide*
   
@@ -209,8 +201,6 @@
 
   $ hg status
   $ hg debugsparse
-  [include]
-  
   [exclude]
   hide*
   
@@ -257,8 +247,6 @@
   $ hg debugsparse
   [include]
   empty
-  [exclude]
-  
   
 
   $ mkdir add
@@ -276,8 +264,6 @@
   [include]
   add
   empty
-  [exclude]
-  
   
   $ hg add -s add/*
   add/foo already tracked!
@@ -288,8 +274,6 @@
   [include]
   add
   empty
-  [exclude]
-  
   
 
   $ cd ..