named branches: server branchmap wire protocol support (issue736)
The repository command, 'branchmap', returns a dictionary, branchname
-> [branchheads], and will be implemented for localrepo, httprepo and
sshrepo.
The following wire format is used for returning data:
branchname1 branch1head2 branch1head2 ...
branchname2 ...
...
Branch names are URL encoded to escape white space, and branch heads
are sent as hex encoded node ids. All branches and all their heads are
sent.
The background and motivation for this command is the desire for a
richer named branch semantics when pushing changesets. The details are
explained in the original proposal which is included below.
1. BACKGROUND
The algorithm currently implemented in Mercurial only considers the
graph theoretical heads when determining whether new heads are
created, rather than using the branch heads as a count (the algorithm
considers a branch head effectively closed when it is merged into
another branch or a new named branch is started from that point
onward).
Our particular problem with the algorithm is that we'd like to see the
following case working without forcing a push:
Upsteam has:
(0:dev) ---- (1:dev)
\
`--- (2:stable)
Someone merges stable into dev:
(0:dev) ---- (1:dev) ------(3:dev)
\ /
`--- (2:stable) --------´
This can be pushed without --force (as it should).
Now someone else does some coding on stable (a bug fix, say):
(0:dev) ---- (1:dev) ------(3:dev)
\ /
`--- (2:stable) ---------´---------(4:stable)
This time we need --force to push.
We allow this to be pushed without using --force by getting all the
remote branch heads (by extending the wire protocol with a new
function).
We would, furthermore, also prefer if it is impossible to push a new
branch without --force (or a later --newbranch option so --force isn't
shoe-horned into too many disparate functions, if need be), except of
course in the case where the remote repository is empty.
This is what our patches accomplish.
2. ALTERNATIVES
We have, of course, considered some alternatives to reconstructing
enough information to decide whether we are creating new remote branch
heads, before we added the new wire protocol command.
2.1. LOOKUP ON REMOTE
The main alternative is to use the information from remote.heads() and
remote.lookup() to try to reconstruct enough graph information to
decide whether we are creating new heads. This is not adequate as
illustrated below.
Remember that each lookup is typically a request-response pair over
SSH or HTTP(S).
If we have a simple repository at the remote end like this:
(0:dev) ---- (1:dev) ---- (3:stable)
\
`--- (2:dev)
then remote.heads() will yield [2, 3]. Assume we have nodes [0, 1, 2]
locally and want to create a new node, 4:dev, as a descendant from
(1:dev), which should be OK as 1:dev is a branch head.
If we do remote.lookup('dev') we will get [2]. Thus, we can get
information about whether a branch exists on the remote server or not,
but this does not solve our problem of figuring out whether we are
creating new heads or not.
Pushing 4:dev ought to be OK, since after the push, we still only have
two heads on branch a.
Using remote.lookup() and remote.heads() is thus not adequate to
consistently decide whether we are creating new remote heads (e.g. in
this situation the latter would never return 1:dev).
2.2. USING INCOMING TO RECONSTRUCT THE GRAPH
An alternative would be to use information equivalent to hg incoming
to get the full remote graph in addition to the local graph.
To do this, we would have to get a changegroup(subset) bundle
representing the remote end (which may be a substantial amount of
data), getting the branch heads from an instantiated bundlerepository,
deleting the bundle, and finally, we can compute the prepush logic.
While this is backwards compatible, it will cause a possibly
substantial slowdown of the push command as it first needs to pull in
all changes.
3. FURTHER ARGUMENTS IN FAVOUR OF THE BRANCHMAP WIRE-PROTOCOL EXTENSION
Currently, the commands incoming and pull, work based on the tip of a
given branch if used with "-r branchname", making it hard to get all
revisions of a certain branch only (if it has multiple heads). This
can be solved by requesting the remote's branchheads and letting the
revisions to be used with the command be these heads. This can be done
by extending the commands with a new option, e.g.:
hg pull -b branchname
which will be turned into the equivalent of:
hg pull -r branchhead1 -r branchhead2 -r branchhead3
We have a simple follow-up patch that can do this ready as well
(although not submitted yet as it is pending the acceptance of the
branch patch).
4. WRAP-UP
We generally find that the branchmap wire protocol extension can
provide better named branch support to Mercurial. Currently, some
things, like the initial push scenario in this mail, are fairly
counter-intuitive, and the more often you have to force push, the more
it is likely you will get a lot of spurious and unnecessary merge
nodes. Also, restricting incoming and pull to all changes on a branch
rather than changes on the tip-most head would be a sensible extension
to making named branches a first class citizen in Mercurial.
Currently, named branches sometimes feel like a late-coming unwanted
step-child.
We have run it in a production environment for a while, with fewer
multiple heads occurring in our repositories and fewer confused users
as a result.
Also, it fixes the long-standing issue 736.
Co-contributor: Sune Foldager <cryo@cyanite.org>
created new head
--------------
test L:up a R:nc a b W: - 1 get local a to b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local e300d1c794ec+ remote 735846fee2d7
searching for copies back to rev 1
unmatched files in other:
b
all copies found (* = to merge, ! = divergent):
b -> a *
checking for directory renames
rev: versions differ -> m
a: remote copied to b -> m
preserving a for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging a and b to b
my b@e300d1c794ec+ other b@735846fee2d7 ancestor a@924404dff337
premerge successful
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@e300d1c794ec+ other rev@735846fee2d7 ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
a
C a
--------------
created new head
--------------
test L:nc a b R:up a W: - 2 get rem change to a and b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ac809aeed39a+ remote f4db7e329e71
searching for copies back to rev 1
unmatched files in local:
b
all copies found (* = to merge, ! = divergent):
b -> a *
checking for directory renames
a: remote is newer -> g
b: local copied to a -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
getting a
picked tool 'python ../merge' for b (binary False symlink False)
merging b and a to b
my b@ac809aeed39a+ other a@f4db7e329e71 ancestor a@924404dff337
premerge successful
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ac809aeed39a+ other rev@f4db7e329e71 ancestor rev@924404dff337
1 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M a
M b
a
--------------
created new head
--------------
test L:up a R:nm a b W: - 3 get local a change to b, remove a
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local e300d1c794ec+ remote e03727d2d66b
searching for copies back to rev 1
unmatched files in other:
b
all copies found (* = to merge, ! = divergent):
b -> a *
checking for directory renames
rev: versions differ -> m
a: remote moved to b -> m
preserving a for resolve of b
preserving rev for resolve of rev
removing a
picked tool 'python ../merge' for b (binary False symlink False)
merging a and b to b
my b@e300d1c794ec+ other b@e03727d2d66b ancestor a@924404dff337
premerge successful
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@e300d1c794ec+ other rev@e03727d2d66b ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
a
--------------
created new head
--------------
test L:nm a b R:up a W: - 4 get remote change to b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ecf3cb2a4219+ remote f4db7e329e71
searching for copies back to rev 1
unmatched files in local:
b
all copies found (* = to merge, ! = divergent):
b -> a *
checking for directory renames
b: local moved to a -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging b and a to b
my b@ecf3cb2a4219+ other a@f4db7e329e71 ancestor a@924404dff337
premerge successful
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ecf3cb2a4219+ other rev@f4db7e329e71 ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
a
--------------
created new head
--------------
test L: R:nc a b W: - 5 get b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local 94b33a1b7f2d+ remote 735846fee2d7
searching for copies back to rev 1
unmatched files in other:
b
all copies found (* = to merge, ! = divergent):
b -> a
checking for directory renames
rev: versions differ -> m
b: remote created -> g
preserving rev for resolve of rev
getting b
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@94b33a1b7f2d+ other rev@735846fee2d7 ancestor rev@924404dff337
1 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
C a
--------------
created new head
--------------
test L:nc a b R: W: - 6 nothing
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ac809aeed39a+ remote 97c705ade336
searching for copies back to rev 1
unmatched files in local:
b
all copies found (* = to merge, ! = divergent):
b -> a
checking for directory renames
rev: versions differ -> m
preserving rev for resolve of rev
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ac809aeed39a+ other rev@97c705ade336 ancestor rev@924404dff337
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
C a
C b
--------------
created new head
--------------
test L: R:nm a b W: - 7 get b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local 94b33a1b7f2d+ remote e03727d2d66b
searching for copies back to rev 1
unmatched files in other:
b
all copies found (* = to merge, ! = divergent):
b -> a
checking for directory renames
a: other deleted -> r
rev: versions differ -> m
b: remote created -> g
preserving rev for resolve of rev
removing a
getting b
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@94b33a1b7f2d+ other rev@e03727d2d66b ancestor rev@924404dff337
1 files updated, 1 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
--------------
created new head
--------------
test L:nm a b R: W: - 8 nothing
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ecf3cb2a4219+ remote 97c705ade336
searching for copies back to rev 1
unmatched files in local:
b
all copies found (* = to merge, ! = divergent):
b -> a
checking for directory renames
rev: versions differ -> m
preserving rev for resolve of rev
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ecf3cb2a4219+ other rev@97c705ade336 ancestor rev@924404dff337
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
C b
--------------
created new head
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test L:um a b R:um a b W: - 9 do merge with ancestor in a
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ec03c2ca8642+ remote 79cc6877a3b7
searching for copies back to rev 1
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@ec03c2ca8642+ other b@79cc6877a3b7 ancestor a@924404dff337
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ec03c2ca8642+ other rev@79cc6877a3b7 ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
--------------
created new head
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test L:nm a b R:nm a c W: - 11 get c, keep b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ecf3cb2a4219+ remote e6abcc1a30c2
searching for copies back to rev 1
unmatched files in local:
b
unmatched files in other:
c
all copies found (* = to merge, ! = divergent):
c -> a !
b -> a !
checking for directory renames
a: divergent renames -> dr
rev: versions differ -> m
c: remote created -> g
preserving rev for resolve of rev
warning: detected divergent renames of a to:
b
c
getting c
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ecf3cb2a4219+ other rev@e6abcc1a30c2 ancestor rev@924404dff337
1 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M c
C b
--------------
created new head
--------------
test L:nc a b R:up b W: - 12 merge b no ancestor
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ac809aeed39a+ remote af30c7647fc7
searching for copies back to rev 1
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@ac809aeed39a+ other b@af30c7647fc7 ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ac809aeed39a+ other rev@af30c7647fc7 ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
C a
--------------
created new head
--------------
test L:up b R:nm a b W: - 13 merge b no ancestor
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local 59318016310c+ remote e03727d2d66b
searching for copies back to rev 1
a: other deleted -> r
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
removing a
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@59318016310c+ other b@e03727d2d66b ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@59318016310c+ other rev@e03727d2d66b ancestor rev@924404dff337
0 files updated, 2 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
--------------
created new head
--------------
test L:nc a b R:up a b W: - 14 merge b no ancestor
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ac809aeed39a+ remote 8dbce441892a
searching for copies back to rev 1
a: remote is newer -> g
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
getting a
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@ac809aeed39a+ other b@8dbce441892a ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ac809aeed39a+ other rev@8dbce441892a ancestor rev@924404dff337
1 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M a
M b
--------------
created new head
--------------
test L:up b R:nm a b W: - 15 merge b no ancestor, remove a
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local 59318016310c+ remote e03727d2d66b
searching for copies back to rev 1
a: other deleted -> r
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
removing a
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@59318016310c+ other b@e03727d2d66b ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@59318016310c+ other rev@e03727d2d66b ancestor rev@924404dff337
0 files updated, 2 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
--------------
created new head
--------------
test L:nc a b R:up a b W: - 16 get a, merge b no ancestor
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ac809aeed39a+ remote 8dbce441892a
searching for copies back to rev 1
a: remote is newer -> g
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
getting a
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@ac809aeed39a+ other b@8dbce441892a ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ac809aeed39a+ other rev@8dbce441892a ancestor rev@924404dff337
1 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M a
M b
--------------
created new head
--------------
test L:up a b R:nc a b W: - 17 keep a, merge b no ancestor
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local 0b76e65c8289+ remote 735846fee2d7
searching for copies back to rev 1
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@0b76e65c8289+ other b@735846fee2d7 ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@0b76e65c8289+ other rev@735846fee2d7 ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
C a
--------------
created new head
--------------
test L:nm a b R:up a b W: - 18 merge b no ancestor
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ecf3cb2a4219+ remote 8dbce441892a
searching for copies back to rev 1
b: versions differ -> m
rev: versions differ -> m
remote changed a which local deleted
use (c)hanged version or leave (d)eleted? c
a: prompt recreating -> g
preserving b for resolve of b
preserving rev for resolve of rev
getting a
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@ecf3cb2a4219+ other b@8dbce441892a ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ecf3cb2a4219+ other rev@8dbce441892a ancestor rev@924404dff337
1 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M a
M b
--------------
created new head
--------------
test L:up a b R:nm a b W: - 19 merge b no ancestor, prompt remove a
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local 0b76e65c8289+ remote e03727d2d66b
searching for copies back to rev 1
local changed a which remote deleted
use (c)hanged version or (d)elete? c
a: prompt keep -> a
b: versions differ -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging b
my b@0b76e65c8289+ other b@e03727d2d66b ancestor b@000000000000
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@0b76e65c8289+ other rev@e03727d2d66b ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
C a
--------------
created new head
--------------
test L:up a R:um a b W: - 20 merge a and b to b, remove a
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local e300d1c794ec+ remote 79cc6877a3b7
searching for copies back to rev 1
unmatched files in other:
b
all copies found (* = to merge, ! = divergent):
b -> a *
checking for directory renames
rev: versions differ -> m
a: remote moved to b -> m
preserving a for resolve of b
preserving rev for resolve of rev
removing a
picked tool 'python ../merge' for b (binary False symlink False)
merging a and b to b
my b@e300d1c794ec+ other b@79cc6877a3b7 ancestor a@924404dff337
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@e300d1c794ec+ other rev@79cc6877a3b7 ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
a
--------------
created new head
--------------
test L:um a b R:up a W: - 21 merge a and b to b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ec03c2ca8642+ remote f4db7e329e71
searching for copies back to rev 1
unmatched files in local:
b
all copies found (* = to merge, ! = divergent):
b -> a *
checking for directory renames
b: local moved to a -> m
rev: versions differ -> m
preserving b for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging b and a to b
my b@ec03c2ca8642+ other a@f4db7e329e71 ancestor a@924404dff337
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ec03c2ca8642+ other rev@f4db7e329e71 ancestor rev@924404dff337
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
a
--------------
created new head
--------------
test L:nm a b R:up a c W: - 23 get c, keep b
--------------
resolving manifests
overwrite None partial False
ancestor 924404dff337 local ecf3cb2a4219+ remote 2b958612230f
searching for copies back to rev 1
unmatched files in local:
b
unmatched files in other:
c
all copies found (* = to merge, ! = divergent):
b -> a *
checking for directory renames
b: local moved to a -> m
rev: versions differ -> m
c: remote created -> g
preserving b for resolve of b
preserving rev for resolve of rev
picked tool 'python ../merge' for b (binary False symlink False)
merging b and a to b
my b@ecf3cb2a4219+ other a@2b958612230f ancestor a@924404dff337
premerge successful
getting c
picked tool 'python ../merge' for rev (binary False symlink False)
merging rev
my rev@ecf3cb2a4219+ other rev@2b958612230f ancestor rev@924404dff337
1 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
--------------
M b
a
M c
--------------