tests/test-git-import

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 <[e-mail]>

#!/bin/sh

hg init a
cd a

echo % new file
hg import -mnew - <<EOF
diff --git a/new b/new
new file mode 100644
index 0000000..7898192
--- /dev/null
+++ b/new
@@ -0,0 +1 @@
+a
EOF

echo % new empty file
hg import -mempty - <<EOF
diff --git a/empty b/empty
new file mode 100644
EOF
hg locate empty

echo % chmod +x
hg import -msetx - <<EOF
diff --git a/new b/new
old mode 100644
new mode 100755
EOF

test -x new || echo failed

echo % copy
hg import -mcopy - <<EOF
diff --git a/new b/copy
old mode 100755
new mode 100644
similarity index 100%
copy from new
copy to copy
diff --git a/new b/copyx
similarity index 100%
copy from new
copy to copyx
EOF

if "$TESTDIR/hghave" -q execbit; then
    test -f copy -a ! -x copy || echo failed
    test -x copyx || echo failed
else
    test -f copy || echo failed
fi
cat copy
hg cat copy

echo % rename
hg import -mrename - <<EOF
diff --git a/copy b/rename
similarity index 100%
rename from copy
rename to rename
EOF

hg locate

echo % delete
hg import -mdelete - <<EOF
diff --git a/copyx b/copyx
deleted file mode 100755
index 7898192..0000000
--- a/copyx
+++ /dev/null
@@ -1 +0,0 @@
-a
EOF

hg locate
test -f copyx && echo failed || true

echo % regular diff
hg import -mregular - <<EOF
diff --git a/rename b/rename
index 7898192..72e1fe3 100644
--- a/rename
+++ b/rename
@@ -1 +1,5 @@
 a
+a
+a
+a
+a
EOF

echo % copy and modify
hg import -mcopymod - <<EOF
diff --git a/rename b/copy2
similarity index 80%
copy from rename
copy to copy2
index 72e1fe3..b53c148 100644
--- a/rename
+++ b/copy2
@@ -1,5 +1,5 @@
 a
 a
-a
+b
 a
 a
EOF

hg cat copy2

echo % rename and modify
hg import -mrenamemod - <<EOF
diff --git a/copy2 b/rename2
similarity index 80%
rename from copy2
rename to rename2
index b53c148..8f81e29 100644
--- a/copy2
+++ b/rename2
@@ -1,5 +1,5 @@
 a
 a
 b
-a
+c
 a
EOF

hg locate copy2
hg cat rename2

echo % one file renamed multiple times
hg import -mmultirenames - <<EOF
diff --git a/rename2 b/rename3
rename from rename2
rename to rename3
diff --git a/rename2 b/rename3-2
rename from rename2
rename to rename3-2
EOF
hg log -vCr. --template '{rev} {files} / {file_copies%filecopy}\n'

hg locate rename2 rename3 rename3-2
hg cat rename3
echo
hg cat rename3-2

echo foo > foo
hg add foo
hg ci -m 'add foo'
echo % binary files and regular patch hunks
hg import -m binaryregular - <<EOF
diff --git a/binary b/binary
new file mode 100644
index 0000000000000000000000000000000000000000..593f4708db84ac8fd0f5cc47c634f38c013fe9e4
GIT binary patch
literal 4
Lc\${NkU|;|M00aO5

diff --git a/foo b/foo2
rename from foo
rename to foo2
EOF
cat foo2
hg manifest --debug | grep binary

echo % many binary files
hg import -m multibinary - <<EOF
diff --git a/mbinary1 b/mbinary1
new file mode 100644
index 0000000000000000000000000000000000000000..593f4708db84ac8fd0f5cc47c634f38c013fe9e4
GIT binary patch
literal 4
Lc\${NkU|;|M00aO5

diff --git a/mbinary2 b/mbinary2
new file mode 100644
index 0000000000000000000000000000000000000000..112363ac1917b417ffbd7f376ca786a1e5fa7490
GIT binary patch
literal 5
Mc\${NkU|\`?^000jF3jhEB

EOF
hg manifest --debug | grep mbinary

echo % filenames with spaces
hg import -m spaces - <<EOF
diff --git a/foo bar b/foo bar
new file mode 100644
index 0000000..257cc56
--- /dev/null
+++ b/foo bar	
@@ -0,0 +1 @@
+foo
EOF
cat "foo bar"

echo % copy then modify the original file
hg import -m copy-mod-orig - <<EOF
diff --git a/foo2 b/foo2
index 257cc56..fe08ec6 100644
--- a/foo2
+++ b/foo2
@@ -1 +1,2 @@
 foo
+new line
diff --git a/foo2 b/foo3
similarity index 100%
copy from foo2
copy to foo3
EOF

cat foo3