Is there a Mercurial equivalent to git log --first-parent?

Question

git log --first-parent omits all but the first parent of merge commits.

Example:

$ git log --oneline --graph

* 087f5ed Master C
*   36c50a2 Merge branch 'feature'
|\  
| * 98c89df Feature B
| * 89b3a7b Feature A
* | 9a95133 Master B
|/  
* 766c9b0 Master A

$ git log --oneline --graph --first-parent

* 087f5ed Master C
* 36c50a2 Merge branch 'feature'
* 9a95133 Master B
* 766c9b0 Master A

Is there a Mercurial equivalent?

Answer 1

Direct equivalent: hg log -r '_firstancestors(...)'

There is a direct equivalent: the hidden revset _firstancestors follows the first-parent (p1) side of each merge. In Mercurial, like in Git, the first parent is the commit that was checked-out when hg merge [second parent] was called.

hg log -r '_firstancestors(myfeature)'

'hidden' means that it starts with an underscore, and is not listed in the help etc., but can still be used if you know it exists. I don't know why it is hidden.

Examples

This revset alias lists all commits on a feature branch while ignoring all the ancestry whenever master is merged into the branch to bring it up-to-date. (The shop I work prefers merging over rebasing).

[revsetalias]
feature($1) = _firstancestors($1) and not _firstancestors(master)

[alias]
f = log -r "feature($(echo $HG_ARGS| sed 's/^f //'))"

Example usage (uses my own logging template):

$ hg f myfeature
o  423 myfeature default/myfeature -- Esteis -- 2016-07-12 -- 123abc
|  this
o    422 -- Esteis -- 2016-07-12 -- 123def
|\   merge master into myfeature
o ~  421 -- Esteis -- 2016-07-12 -- 456abc
|    that
o  420 -- Esteis -- 2016-07-12 -- 789def
|  and the other

Answer 2

>hg glog -r 410:426 --template "{rev} - {desc|firstline|fill68}\n"
o    426 - Merge test fixes for dulwich changes and output changes.
|\
| o    425 - Merge incoming fix.
| |\
| | o  424 - getremotechanges: fix incoming support
| | |
o | |  423 - overlay: stop using deprecated tree.entries() method
| | |
| o |  422 - Fix all-version-tests.
| | |
o | |  421 - Test output format tweaks for test-outgoing.
| | |
o | |  420 - test-incoming: fixes for hg 1.7
| | |
| o |    419 - Merge fix for `hg out` failing on empty repo.
| |\ \
| | o |  418 - In some situations where a reference is being used but does not
| | | |  exist in _map_git or _map_hg, silently skip the reference rather
| | | |  than throwing an error. This allows hg outgoing to work on
| | | |  repositories which do not contain any revisions at all.
| o | |  417 - only want heads and tags
| |/ /
| o |  416 - test-url-parsing: update expecations missed by edaadbd99074
| | |
| o |  415 - to be recognized port number in path to repository
| | |
| o |  414 - Unbreak outgoing to non-git repos with hg pre-1.9
| | |
| o |  413 - test fixes for progress cleanup
| |/
| o  412 - Fix mercurial issue2855
| |
| o  411 - Convert dulwich progress into mercurial ui.progress
|/
o  410 - test-incoming: only run on hg 1.7.x and newer

Instead of extremely degenerated case from gist, I use part of real repository DAG (hg-git repository). I hope, the selection is sufficiently indicative for the problem being solved.

Needed revset (in plain English) will be

"Range A:B without second parent and it's ancestors for mergesets"

In revset functional language (TBT!)

-r "410::426 - (p2(merge()) or ancestors(p2(merge())))"

In case of the full range of changesets as source more readable form will be something like

hg log -r "!(p2(merge()) or ancestors(p2(merge())))"

Edit 1

I tested revset, rethought about methodology (instead of excluding I want only add needed to empty set), nearest iteration for my use-case for now (have bugs, can't find solution) is

(p1(ancestors(p1(426))) or p1(426) or 426) and 410::426

which (still) include some unwanted revisions

Answer 3

hg log --follow-first seems to do roughly the same thing, with a few provisions:

1. It's deprecated (with no explanation that I can find).

2. I can't figure out how to get it to display anything other than just the straight-line history from the current changeset (e.g. display history following the first parent from two divergent heads (the equivalent of git log --first-parent branch-a branch-b), although this may be just because of my lack of knowledge of Mercurial.

3. It shows empty branch lines with hg log -G:

   $ hg log -G --template '{node|short} {desc|firstline}'
   
   @  51b90923fc9d Master C
   |
   o    bb51d979fd68 Merge branch 'feature'
   |\
   | o  a9ca2597ebbc Feature B
   | |
   | o  d0a54af09272 Feature A
   | |
   o |  77ceb31100be Master B
   |/
   o  b5a0b2c7468f Master A
   
   $ hg log -G --template '{node|short} {desc|firstline}' --follow-first
   
   @  51b90923fc9d Master C
   |
   o    bb51d979fd68 Merge branch 'feature'
   |\
   o |  77ceb31100be Master B
   |/
   o  b5a0b2c7468f Master A
   

   The above example may not seem too bad, but see https://gist.github.com/MaxNanasy/5184202 for an example in which this behavior renders unwieldy output.

   This issue may not matter much if issue #2 is insurmountable, because then hg log without -G would be the only useful way to use --follow-first AFAICT.

Answer 4

You can use revsets for this:

hg log -r "p1(merge())"

merge() gets all the merge commits and p1() gets the first parent of those commits.

Use hg help revsets to get more information on revsets.