fetch: use dirstate branch instead of first parents

hgext/fetch.py

@@ -33,8 +33,9 b" def fetch(ui, repo, source='default', **"
         opts['date'] = util.parsedate(date)
 
     parent, p2 = repo.dirstate.parents()
-    branch = repo[parent].branch()
-    if parent != repo[branch].node():
+    branch = repo.dirstate.branch()
+    branchnode = repo.branchtags().get(branch)
+    if parent != branchnode:
         raise util.Abort(_('working dir not at branch tip '
                            '(use "hg update" to check out branch tip)'))
 

tests/test-fetch

@@ -156,4 +156,17 b" echo '% parent should be 3 (fetch did no"
 hg -R n2 parents --template '{rev}\n'
 rm -fr n1 n2
 
+echo % pull in change on different branch than dirstate
+hg init n1
+echo a > n1/a
+hg -R n1 ci -Am initial
+hg clone n1 n2
+echo b > n1/a
+hg -R n1 ci -m next
+hg -R n2 branch topic
+hg -R n2 fetch -d '0 0' -m merge n1
+echo '% parent should be 0 (fetch did not update or merge anything)'
+hg -R n2 parents --template '{rev}\n'
+rm -fr n1 n2
+
 true

tests/test-fetch.out

@@ -170,3 +170,11 b' added 3 changesets with 2 changes to 1 f'
 not merging with 1 other new branch heads (use "hg heads ." and "hg merge" to merge them)
 % parent should be 3 (fetch did not merge anything)
 3
+% pull in change on different branch than dirstate
+adding a
+updating working directory
+1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+marked working directory as branch topic
+abort: working dir not at branch tip (use "hg update" to check out branch tip)
+% parent should be 0 (fetch did not update or merge anything)
+0