Re: Diffing submodule does not yield complete logs for merge commits

[Robert Dailey <rcdailey.lists@gmail.com>]

On Fri, May 1, 2015 at 12:57 PM, Heiko Voigt <hvoigt@hvoigt.net> wrote:
> Hi,
>
> On Wed, Apr 29, 2015 at 03:53:11PM -0500, Robert Dailey wrote:
>> I am attempting to diff a submodule modified in my working copy and
>> the only difference is a merge commit. However, I do not get the
>> "full" range of commits introduced by the merge commit when I diff it:
>>
>> $ git diff --submodule=log Core
>> Submodule Core 8b4ec60..def2f3b:
>>   > Merge remote-tracking branch 'origin/master-ah3k'
>>
>> However if I go inside my submodule and run `git log` by hand, I get
>> more information about the TRUE commits introduced:
>>
>> $ git log --oneline 8b4ec60..def2f3b
>> def2f3b Merge remote-tracking branch 'origin/master-ah3k'
>> 015c961 Remove log spam in FontManager
>> 7713ba1 Update third party submodule to latest
>> 10aac78 Merge pull request #9 in FE/core from
>> feature/FE-1348-selecting-continue-on-zero-balance to master-ah3k
>> 287882f FE-1376 Nedd to remain in check detail screen when selecting
>> donation after SBI
>> a5a6bed Do not overwrite the current check# within loop
>> dfb8547 Adding list of checks to CRspChecks before saving
>> 1be280a FE-1354: Guest logged out in specific multiple check scenario
>> de06d5a [FE-1348] Fix PATT exit while checks still open
>>
>> It's almost as if the `git diff --submodule=log` approach is passing
>> in --first-parent to git log, which would exclude commits in the range
>> that I'm seeing when I run git log manually.
>
> That is exactly the case. In prepare_submodule_summary() that option is
> set before doing the revision walk.
>
>> Is this by design? Is there a way to enable the full log history with
>> `git diff` on a submodule?
>
> This stems from the first implementation for showing submodule diffs in
> commit 752c0c24. I guess this was done deliberately to limit the amount
> of output you get for a submodule. At the moment this is hardcoded but I
> think there is nothing wrong with adding another option to include the
> full log.
>
> Cheers Heiko

I will go ahead and work on this feature. Here is what I'd like to see:

1. `git diff --submodule` should have the ability to display full logs
vs current logs (i.e. without --first-parent)
2. `git submodule summary` should have an option to display full logs
or "first-parent" logs.

For #1, do you recommend adding a 3rd setting for `diff.submodule`
config? Something like "full-log" or something? Or an entirely new
config? I noticed that in diff.h, the DIFF_OPT flags already consume
31 bits. If this is a 32-bit flag, there is only 1 bit left. If we go
with a 3rd setting for `diff.submodule` I think this might consume the
last bit.

We could also make `git diff --submodule` default to the "full log"
type, and if users want only first parent logs in submodule summary,
they'd have to execute `git submodule summary` instead.

There are a few options. What do you recommend? Thanks.