$ branchcache=.hg/cache/branchheads

  $ listbranchcaches() {

  >    for f in .hg/cache/branchheads*;

  >       do echo === $f ===;

  >       cat $f;

  >     done;

  > }

  $ purgebranchcaches() {

  >     rm .hg/cache/branchheads*

  > }

  $ hg init t

  $ cd t

  $ hg branches

  $ echo foo > a

  $ hg add a

  $ hg ci -m "initial"

  $ hg branch foo

  marked working directory as branch foo

  (branches are permanent and global, did you want a bookmark?)

  $ hg branch

  foo

  $ hg ci -m "add branch name"

  $ hg branch bar

  marked working directory as branch bar

  (branches are permanent and global, did you want a bookmark?)

  $ hg ci -m "change branch name"

Branch shadowing:

  $ hg branch default

  abort: a branch of the same name already exists

  (use 'hg update' to switch to it)

  [255]

  $ hg branch -f default

  marked working directory as branch default

  (branches are permanent and global, did you want a bookmark?)

  $ hg ci -m "clear branch name"

  created new head

There should be only one default branch head

  $ hg heads .

  changeset:   3:1c28f494dae6

  tag:         tip

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     clear branch name

  $ hg co foo

  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg branch

  foo

  $ echo bleah > a

  $ hg ci -m "modify a branch"

  $ hg merge default

  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ hg branch

  foo

  $ hg ci -m "merge"

  $ hg log

  changeset:   5:530046499edf

  branch:      foo

  tag:         tip

  parent:      4:adf1a74a7f7b

  parent:      3:1c28f494dae6

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     merge

  changeset:   4:adf1a74a7f7b

  branch:      foo

  parent:      1:6c0e42da283a

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     modify a branch

  changeset:   3:1c28f494dae6

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     clear branch name

  changeset:   2:c21617b13b22

  branch:      bar

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     change branch name

  changeset:   1:6c0e42da283a

  branch:      foo

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     add branch name

  changeset:   0:db01e8ea3388

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     initial

  $ hg branches

  foo                            5:530046499edf

  default                        3:1c28f494dae6 (inactive)

  bar                            2:c21617b13b22 (inactive)

  $ hg branches -q

  foo

  default

  bar

Test for invalid branch cache:

  $ hg rollback

  repository tip rolled back to revision 4 (undo commit)

  working directory now based on revisions 4 and 3

  $ cp ${branchcache}-unserved .hg/bc-invalid

  $ hg log -r foo

  changeset:   4:adf1a74a7f7b

  branch:      foo

  tag:         tip

  parent:      1:6c0e42da283a

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     modify a branch

  $ cp .hg/bc-invalid $branchcache

  $ hg --debug log -r foo

  changeset:   4:adf1a74a7f7b4cd193d12992f5d0d6a004ed21d6

  branch:      foo

  tag:         tip

  phase:       draft

  parent:      1:6c0e42da283a56b5edc5b4fadb491365ec7f5fa8

  parent:      -1:0000000000000000000000000000000000000000

  manifest:    1:8c342a37dfba0b3d3ce073562a00d8a813c54ffe

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  files:       a

  extra:       branch=foo

  description:

  modify a branch

  $ purgebranchcaches

  $ echo corrupted > $branchcache

  $ hg log -qr foo

  4:adf1a74a7f7b

  $ listbranchcaches

  === .hg/cache/branchheads ===

  corrupted

  === .hg/cache/branchheads-unserved ===

  adf1a74a7f7b4cd193d12992f5d0d6a004ed21d6 4

  1c28f494dae69a2f8fc815059d257eccf3fcfe75 default

  adf1a74a7f7b4cd193d12992f5d0d6a004ed21d6 foo

  c21617b13b220988e7a2e26290fbe4325ffa7139 bar

Push should update the branch cache:

  $ hg init ../target

Pushing just rev 0:

  $ hg push -qr 0 ../target

  $ (cd ../target/; listbranchcaches)

  === .hg/cache/branchheads-impactable ===

  db01e8ea3388fd3c7c94e1436ea2bd6a53d581c5 0

  db01e8ea3388fd3c7c94e1436ea2bd6a53d581c5 default

Pushing everything:

  $ hg push -qf ../target

  $ (cd ../target/; listbranchcaches)

  === .hg/cache/branchheads-impactable ===

  adf1a74a7f7b4cd193d12992f5d0d6a004ed21d6 4

  1c28f494dae69a2f8fc815059d257eccf3fcfe75 default

  adf1a74a7f7b4cd193d12992f5d0d6a004ed21d6 foo

  c21617b13b220988e7a2e26290fbe4325ffa7139 bar

Update with no arguments: tipmost revision of the current branch:

  $ hg up -q -C 0

  $ hg up -q

  $ hg id

  1c28f494dae6

  $ hg up -q 1

  $ hg up -q

  $ hg id

  adf1a74a7f7b (foo) tip

  $ hg branch foobar

  marked working directory as branch foobar

  (branches are permanent and global, did you want a bookmark?)

  $ hg up

  abort: branch foobar not found

  [255]

Fastforward merge:

  $ hg branch ff

  marked working directory as branch ff

  (branches are permanent and global, did you want a bookmark?)

  $ echo ff > ff

  $ hg ci -Am'fast forward'

  adding ff

  $ hg up foo

  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg merge ff

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ hg branch

  foo

  $ hg commit -m'Merge ff into foo'

  $ hg parents

  changeset:   6:185ffbfefa30

  branch:      foo

  tag:         tip

  parent:      4:adf1a74a7f7b

  parent:      5:1a3c27dc5e11

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     Merge ff into foo

  $ hg manifest

  a

  ff

Test merging, add 3 default heads and one test head:

  $ cd ..

  $ hg init merges

  $ cd merges

  $ echo a > a

  $ hg ci -Ama

  adding a

  $ echo b > b

  $ hg ci -Amb

  adding b

  $ hg up 0

  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo c > c

  $ hg ci -Amc

  adding c

  created new head

  $ hg up 0

  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo d > d

  $ hg ci -Amd

  adding d

  created new head

  $ hg up 0

  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg branch test

  marked working directory as branch test

  (branches are permanent and global, did you want a bookmark?)

  $ echo e >> e

  $ hg ci -Ame

  adding e

  $ hg log

  changeset:   4:3a1e01ed1df4

  branch:      test

  tag:         tip

  parent:      0:cb9a9f314b8b

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     e

  changeset:   3:980f7dc84c29

  parent:      0:cb9a9f314b8b

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     d

  changeset:   2:d36c0562f908

  parent:      0:cb9a9f314b8b

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     c

  changeset:   1:d2ae7f538514

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     b

  changeset:   0:cb9a9f314b8b

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     a

Implicit merge with test branch as parent:

  $ hg merge

  abort: branch 'test' has one head - please merge with an explicit rev

  (run 'hg heads' to see all heads)

  [255]

  $ hg up -C default

  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

Implicit merge with default branch as parent:

  $ hg merge

  abort: branch 'default' has 3 heads - please merge with an explicit rev

  (run 'hg heads .' to see heads)

  [255]

3 branch heads, explicit merge required:

  $ hg merge 2

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ hg ci -m merge

2 branch heads, implicit merge works:

  $ hg merge

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ cd ..