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Re: [PATCH v3] Add code to Mercurial VCS backend to show topic if there is any.

On 2020-06-21 14:25, Daniel Shahaf wrote:
Manuel Jacob wrote on Sun, 21 Jun 2020 13:17 +0200:
On 2020-06-20 12:43, Daniel Shahaf wrote:
> Manuel Jacob wrote on Sat, 20 Jun 2020 01:31 +0200:
>> "Topics" is an experimental concept in Mercurial that augments the
>> current branching concept (called "named branches").
>> For more information, see the not always up-to-date Mercurial Wiki
>> page
>> https://www.mercurial-scm.org/wiki/TopicPlan.
>> ---
>>  Functions/VCS_Info/Backends/VCS_INFO_get_data_hg | 10 +++++++++-
>>  1 file changed, 9 insertions(+), 1 deletion(-)
>> diff --git a/Functions/VCS_Info/Backends/VCS_INFO_get_data_hg
>> b/Functions/VCS_Info/Backends/VCS_INFO_get_data_hg
>> index cd5ef321d..deeb331a0 100644
>> --- a/Functions/VCS_Info/Backends/VCS_INFO_get_data_hg
>> +++ b/Functions/VCS_Info/Backends/VCS_INFO_get_data_hg
>> @@ -5,7 +5,7 @@
>>  setopt localoptions extendedglob NO_shwordsplit
>> -local hgbase bmfile branchfile rebasefile dirstatefile mqseriesfile \
>> +local hgbase bmfile branchfile topicfile rebasefile dirstatefile
>> mqseriesfile \
>>      curbmfile curbm \
>>      mqstatusfile mqguardsfile patchdir mergedir \
>>      r_csetid r_lrev r_branch i_bmhash i_bmname \
>> @@ -27,6 +27,7 @@ mergedir="${hgbase}/.hg/merge/"
>>  bmfile="${hgbase}/.hg/bookmarks"
>>  curbmfile="${hgbase}/.hg/bookmarks.current"
>>  branchfile="${hgbase}/.hg/branch"
>> +topicfile="${hgbase}/.hg/topic"
>>  rebasefile="${hgbase}/.hg/rebasestate"
>>  dirstatefile="${hgbase}/.hg/dirstate"
>>  mqstatusfile="${patchdir}/status" # currently applied patches
>> @@ -69,6 +70,13 @@ fi
>>  # If we still don't know the branch it's safe to assume default
>>  [[ -n ${r_branch} ]] || r_branch="default"
>> +# Show topic if there is any (the UI for this experimental concept is
>> not yet
>> +# final, but for a long time the convention has been to join the
>> branch name
>> +# and the topic name by a colon)
>> +if [[ -f ${topicfile} && -r ${topicfile} && -s ${topicfile} ]] ; then
>> +    r_branch=${r_branch}:$(head -n 1 ${topicfile})
>> +fi
> I'm happy to read the file directly, despite experimentality, given the
> discussion elsethread that you'll propose a corresponding unit test to
> the upstream maintainers.
> Using $(head) forks, and we try to avoid forks because they're
> expensive
> on some platforms.  In this case, you could use «IFS= read -r REPLY
> <$topicfile» instead.  (The construct «$(<foo)», just above the hunk
> context, is special-cased to not fork.)

Is there anything special about `REPLY`? It seems to be a convention.
Could I also use e.g. TOPIC?

Yes, $REPLY is merely a convention (see zshparam(1)).  You could use
$topic (lowercase) instead; $TOPIC (uppercase) would not be idiomatic.

> As written, existing set-branch-format hooks would see the
> ${hook_com[branch]}
> input argument set to strings such as "default:mytopic".  Would this
> behaviour be expected, or would people rather expect
> ${hook_com[branch]}
> to be set to strings such as "default" even when .hg/topic exists, and
> to have a new ${hook_com[foo]} key whose value would be "mytopic" (or
> possibly "default:mytopic")?  This would affect the API to hooks but
> would not affect the final output.

If the topic extension is enabled, the meaning of places using branch
names is changed.
When determining how many heads a branch has (e.g. when warning that
another head will be created), each "branch:topic" (or simply "branch"
if there’s no topic) is considered separately.
When specifying a revision, "branch:topic" refers to the head of the
branch with branch name "branch" and topic name "topic", while "branch" refers to the headmost revision with branch name "branch" but no topic.

An example:


Assume that all three changesets have the "branch" field set to
"develop". B has topic "feature1" and C has topic "feature2".

* "develop" refers to A
* "develop:feature1" refers to B
* "develop:feature2" refers to C

If the user updated to B, but the prompt shows "develop" (this is
currently the case), it would be misleading. I don’t know all
possibilities in which the hooks use `${hook_com[branch]}`, but I’d
expect that including the topic would be correct in more cases than not
including it.

Thanks for the walkthrough.  Agreed.  Might want to state on
Doc/Zsh/contrib.yo:1331 that in the hg backend the topic is included,

Since the topic name is hg-specific but the line in the documentation applies to all backends, I’ll keep it short (I’ll spare details about the exact format).

> Similarly, as written, the %b expando in "formats", "actionformats",
> and
> "branchformat" will always be replaced with a string such as
> "default:mytopic".  If someone wants to change the format,¹ they won't
> be able to achieve that using zstyle settings alone; they'd have to
> write an appropriate vcs_info hook in their zshrc.  What do you think
> of, say, making the topic name available as a separate expando in
> branchformat?  Again, this would not affect the default output, but
> make
> customizations easier to implement.
> ¹ Use-cases for changing the format include: colouring "default" and
> "mytopic" differently (compare «zstyle '*' branchformat '%B%b%%b
> %U%r%u'»
> when the get-revision style is set); changing the colon to a space for
> readability or copypasteability; and perhaps even eliding the topic
> name entirely(?).

For the reasons stated above, the topic name should be included. The
colon should also stay because the combined "branch:topic" can be passed
as a revision identifier to various places. Coloring branch and topic
differently wouldn’t be "wrong", but since the "branch:topic" mostly
makes sense together, personally I’d like to have it in the same

I see: if "branch:topic" mostly appears as an atomic unit, it makes
sense that most people will want to color it atomically.

That's all, I think.  I don't foresee any blocks to merging v4 when you
post it.



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