merge: back out single-parent fast-forward merge

This backs out

 changeset:   13158:9e7e24052745
 user:        Mads Kiilerich <[e-mail]>
 date:        Tue Dec 07 03:29:21 2010 +0100
 summary:     merge: fast-forward merge with descendant

Before named branches, the invariants were:

a) "merges" always have two parents
b) p1 is not linearly related to p2

Adding named branches made (b) problematic, so the above patch was
introduced, which fixed (b) but broke (a).

After discussion, we decided that the invariants should be:

a) "merges" always have two parents
b) p1 is not linearly related to p2 OR p1 and p2 are on different branches

mercurial/merge.py

@@ -540,7 +540,7 b' def update(repo, node, branchmerge, forc'
         action += manifestmerge(repo, wc, p2, pa, overwrite, partial)
 
         ### apply phase
-        if not branchmerge or fastforward: # just jump to the new rev
+        if not branchmerge: # just jump to the new rev
             fp1, fp2, xp1, xp2 = fp2, nullid, xp2, ''
         if not partial:
             repo.hook('preupdate', throw=True, parent1=xp1, parent2=xp2)
@@ -549,7 +549,7 b' def update(repo, node, branchmerge, forc'
 
         if not partial:
             repo.dirstate.setparents(fp1, fp2)
-            recordupdates(repo, action, branchmerge and not fastforward)
+            recordupdates(repo, action, branchmerge)
             if not branchmerge and not fastforward:
                 repo.dirstate.setbranch(p2.branch())
     finally:

tests/test-issue619.t

@@ -19,12 +19,7 b' Fast-forward:'
   $ hg merge b
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
-  $ hg branch
-  default
-  $ hg parent --template '{rev}:{node|short} {branches}: {desc}\n'
-  1:06c2121185be b: b
   $ hg ci -Ammerge
-  created new head
 
 Bogus fast-forward should fail:
 

tests/test-newbranch.t

@@ -209,11 +209,12 b' Fastforward merge:'
   $ hg branch
   foo
   $ hg commit -m'Merge ff into foo'
-  created new head
   $ hg parents
-  changeset:   6:6af8030670c9
+  changeset:   6:917eb54e1b4b
   branch:      foo
   tag:         tip
+  parent:      4:98d14f698afe
+  parent:      5:6683a60370cb
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     Merge ff into foo

tests/test-push-warn.t

@@ -413,7 +413,6 b' Check prepush logic with merged branches'
   (branch merge, don't forget to commit)
 
   $ hg -R k ci -m merge
-  created new head
 
   $ hg -R k push -r a j
   pushing to j