threads / patch / 62982

v2merge-strategies.adoc: detail submodule merge

Subject: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

## tl;dr

9 messages between Feb 20, 2025 and Feb 24, 2025. Diffs are folded; open one to read it.

replies: 8people: 5as markdown or json

Lucas Seiki Oshiro· Feb 20, 2025, 15:12 UTC · lore

Submodule merges are, in general, similar to other merges based on oid three-way-merge. When a conflict happens, however, Git has two special cases (introduced in 68d03e4a6e44) on handling the conflict before yielding it to the user. From the merge-ort and merge-recursive sources:

- "Case #1: a is contained in b or vice versa": both strategies try to
perform a fast-forward in the submodules if the commit referred by the
conflicted submodule is descendant of another;
- "Case #2: There are one or more merges that contain a and b in the
submodule.  If there is only one, then present it as a suggestion to the
user, but leave it marked unmerged so the user needs to confirm the
resolution."
Add a small paragraph on merge-strategies.adoc describing this behavior.
Helped-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
---

This v2 changes the documentation text to a clearer explanation (as suggested in the v1 review), and changes its location to merge-strategies.adoc instead of git-merge.adoc.

This content is duplicated as this works for both `ort` and `recursive` strategies.

 Documentation/merge-strategies.adoc | 15 ++++++++++++++
 1 file changed, 14 insertions(+)
Show changes to Documentation/merge-strategies.adoc +14 −0
diff --git a/Documentation/merge-strategies.adoc b/Documentation/merge-strategies.adoc
index 5fc54ec060..a7fca249e2 100644
--- a/Documentation/merge-strategies.adoc
+++ b/Documentation/merge-strategies.adoc
@@ -21,6 +21,13 @@ ort::
 	("Ostensibly Recursive's Twin") and came from the fact that it
 	was written as a replacement for the previous default
 	algorithm, `recursive`.
+
+        In the case where the path is a submodule, if the submodule commit
+        used on one side of the merge is a descendant of the submodule
+        commit used on the other side of the merge, Git attempts to
+        fast-forward to the descendant. Otherwise, Git will treat this case
+        as a conflict, suggesting as a resolution a submodule commit that
+        is descendant of the conflicting ones, if one exists.
 +
 The 'ort' strategy can take the following options:
 
@@ -95,6 +102,13 @@ recursive::
 	renames.  It does not make use of detected copies.  This was
 	the default strategy for resolving two heads from Git v0.99.9k
 	until v2.33.0.
+
+        In the case where the path is a submodule, if the submodule commit
+        used on one side of the merge is a descendant of the submodule
+        commit used on the other side of the merge, Git attempts to
+        fast-forward to the descendant. Otherwise, Git will treat this case
+        as a conflict, suggesting as a resolution a submodule commit that
+        is descendant of the conflicting ones, if one exists.
 +
 The 'recursive' strategy takes the same options as 'ort'.  However,
 there are three additional options that 'ort' ignores (not documented

-- 
2.39.5 (Apple Git-154)
D. Ben Knoble· Feb 20, 2025, 18:46 UTC · re: Lucas Seiki Oshiro · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

On Thu, Feb 20, 2025 at 10:14 AM Lucas Seiki Oshiro <lucasseikioshiro@gmail.com> wrote:

Show 24 quoted lines
>
> Submodule merges are, in general, similar to other merges based on oid
> three-way-merge. When a conflict happens, however, Git has two special
> cases (introduced in 68d03e4a6e44) on handling the conflict before
> yielding it to the user. From the merge-ort and merge-recursive sources:
>
> - "Case #1: a is contained in b or vice versa": both strategies try to
> perform a fast-forward in the submodules if the commit referred by the
> conflicted submodule is descendant of another;
>
> - "Case #2: There are one or more merges that contain a and b in the
> submodule.  If there is only one, then present it as a suggestion to the
> user, but leave it marked unmerged so the user needs to confirm the
> resolution."
>
> Add a small paragraph on merge-strategies.adoc describing this behavior.
>
> Helped-by: Elijah Newren <newren@gmail.com>
> Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
> ---
>
> This v2 changes the documentation text to a clearer explanation (as
> suggested in the v1 review), and changes its location to
> merge-strategies.adoc instead of git-merge.adoc.
This version is clearer to me at least, thanks!
Show 37 quoted lines
>
> This content is duplicated as this works for both `ort` and `recursive`
> strategies.
>
>  Documentation/merge-strategies.adoc | 15 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/Documentation/merge-strategies.adoc b/Documentation/merge-strategies.adoc
> index 5fc54ec060..a7fca249e2 100644
> --- a/Documentation/merge-strategies.adoc
> +++ b/Documentation/merge-strategies.adoc
> @@ -21,6 +21,13 @@ ort::
>         ("Ostensibly Recursive's Twin") and came from the fact that it
>         was written as a replacement for the previous default
>         algorithm, `recursive`.
> +
> +        In the case where the path is a submodule, if the submodule commit
> +        used on one side of the merge is a descendant of the submodule
> +        commit used on the other side of the merge, Git attempts to
> +        fast-forward to the descendant. Otherwise, Git will treat this case
> +        as a conflict, suggesting as a resolution a submodule commit that
> +        is descendant of the conflicting ones, if one exists.
>  +
>  The 'ort' strategy can take the following options:
>
> @@ -95,6 +102,13 @@ recursive::
>         renames.  It does not make use of detected copies.  This was
>         the default strategy for resolving two heads from Git v0.99.9k
>         until v2.33.0.
> +
> +        In the case where the path is a submodule, if the submodule commit
> +        used on one side of the merge is a descendant of the submodule
> +        commit used on the other side of the merge, Git attempts to
> +        fast-forward to the descendant. Otherwise, Git will treat this case
> +        as a conflict, suggesting as a resolution a submodule commit that
> +        is descendant of the conflicting ones, if one exists.
>  +

I'm not particularly a fan of duplicated documentation text: is there a way to reuse one from the other or have one refer/link to the other?

-- 
D. Ben Knoble
Junio C Hamano· Feb 20, 2025, 19:12 UTC · re: Lucas Seiki Oshiro · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

Lucas Seiki Oshiro <lucasseikioshiro@gmail.com> writes:
Show 47 quoted lines
> Submodule merges are, in general, similar to other merges based on oid
> three-way-merge. When a conflict happens, however, Git has two special
> cases (introduced in 68d03e4a6e44) on handling the conflict before
> yielding it to the user. From the merge-ort and merge-recursive sources:
>
> - "Case #1: a is contained in b or vice versa": both strategies try to
> perform a fast-forward in the submodules if the commit referred by the
> conflicted submodule is descendant of another;
>
> - "Case #2: There are one or more merges that contain a and b in the
> submodule.  If there is only one, then present it as a suggestion to the
> user, but leave it marked unmerged so the user needs to confirm the
> resolution."
>
> Add a small paragraph on merge-strategies.adoc describing this behavior.
>
> Helped-by: Elijah Newren <newren@gmail.com>
> Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
> ---
>
> This v2 changes the documentation text to a clearer explanation (as
> suggested in the v1 review), and changes its location to
> merge-strategies.adoc instead of git-merge.adoc.
>
> This content is duplicated as this works for both `ort` and `recursive`
> strategies.
>
>  Documentation/merge-strategies.adoc | 15 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/Documentation/merge-strategies.adoc b/Documentation/merge-strategies.adoc
> index 5fc54ec060..a7fca249e2 100644
> --- a/Documentation/merge-strategies.adoc
> +++ b/Documentation/merge-strategies.adoc
> @@ -21,6 +21,13 @@ ort::
>  	("Ostensibly Recursive's Twin") and came from the fact that it
>  	was written as a replacement for the previous default
>  	algorithm, `recursive`.
> +
> +        In the case where the path is a submodule, if the submodule commit
> +        used on one side of the merge is a descendant of the submodule
> +        commit used on the other side of the merge, Git attempts to
> +        fast-forward to the descendant. Otherwise, Git will treat this case
> +        as a conflict, suggesting as a resolution a submodule commit that
> +        is descendant of the conflicting ones, if one exists.
>  +
>  The 'ort' strategy can take the following options:

I am not going to comment on the text, but as to the formatting, I'd point out that the existing

    +
    The 'ort' strategy can ...

construct, i.e. a line with only '+' on it, followed by left-aligned block of text, is how AsciiDoc wants our second and subsequent paragraphs for an enumerated list of explanations. Here, the existing "The 'ort' strategy can ..." is the second paragraph that follows the paragraph that ends with "... previous default algorithm, 'recursive'", which is the explanation for the item with "ort::" heading.

So, you'd need to (1) change the empty line at the beginning of your added text to have one '+' and nothing else on it, and (2) dedent the rest of the text you added to abut the left edge of the page. Ditto for the other hunk on "recursive::".

Thanks.
Jean-Noël Avila· Feb 21, 2025, 10:17 UTC · re: Lucas Seiki Oshiro · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

Le 20/02/2025 à 16:12, Lucas Seiki Oshiro a écrit :
Show 62 quoted lines
> Submodule merges are, in general, similar to other merges based on oid
> three-way-merge. When a conflict happens, however, Git has two special
> cases (introduced in 68d03e4a6e44) on handling the conflict before
> yielding it to the user. From the merge-ort and merge-recursive sources:
> 
> - "Case #1: a is contained in b or vice versa": both strategies try to
> perform a fast-forward in the submodules if the commit referred by the
> conflicted submodule is descendant of another;
> 
> - "Case #2: There are one or more merges that contain a and b in the
> submodule.  If there is only one, then present it as a suggestion to the
> user, but leave it marked unmerged so the user needs to confirm the
> resolution."
> 
> Add a small paragraph on merge-strategies.adoc describing this behavior.
> 
> Helped-by: Elijah Newren <newren@gmail.com>
> Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
> ---
> 
> This v2 changes the documentation text to a clearer explanation (as
> suggested in the v1 review), and changes its location to
> merge-strategies.adoc instead of git-merge.adoc.
> 
> This content is duplicated as this works for both `ort` and `recursive`
> strategies.
> 
>  Documentation/merge-strategies.adoc | 15 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/Documentation/merge-strategies.adoc b/Documentation/merge-strategies.adoc
> index 5fc54ec060..a7fca249e2 100644
> --- a/Documentation/merge-strategies.adoc
> +++ b/Documentation/merge-strategies.adoc
> @@ -21,6 +21,13 @@ ort::
>  	("Ostensibly Recursive's Twin") and came from the fact that it
>  	was written as a replacement for the previous default
>  	algorithm, `recursive`.
> +
> +        In the case where the path is a submodule, if the submodule commit
> +        used on one side of the merge is a descendant of the submodule
> +        commit used on the other side of the merge, Git attempts to
> +        fast-forward to the descendant. Otherwise, Git will treat this case
> +        as a conflict, suggesting as a resolution a submodule commit that
> +        is descendant of the conflicting ones, if one exists.
>  +
>  The 'ort' strategy can take the following options:
>  
> @@ -95,6 +102,13 @@ recursive::
>  	renames.  It does not make use of detected copies.  This was
>  	the default strategy for resolving two heads from Git v0.99.9k
>  	until v2.33.0.
> +
> +        In the case where the path is a submodule, if the submodule commit
> +        used on one side of the merge is a descendant of the submodule
> +        commit used on the other side of the merge, Git attempts to
> +        fast-forward to the descendant. Otherwise, Git will treat this case
> +        as a conflict, suggesting as a resolution a submodule commit that
> +        is descendant of the conflicting ones, if one exists.
>  +
>  The 'recursive' strategy takes the same options as 'ort'.  However,
>  there are three additional options that 'ort' ignores (not documented

If both chunks are meant to be kept identical, I would recommend to define an attribute (see https://docs.asciidoctor.org/asciidoc/latest/attributes/custom-attributes/) and use it at both sites.

Thanks.
Junio C Hamano· Feb 21, 2025, 18:07 UTC · re: Jean-Noël Avila · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

Jean-Noël Avila <jn.avila@free.fr> writes:
Show 20 quoted lines
>> @@ -95,6 +102,13 @@ recursive::
>>  	renames.  It does not make use of detected copies.  This was
>>  	the default strategy for resolving two heads from Git v0.99.9k
>>  	until v2.33.0.
>> +
>> +        In the case where the path is a submodule, if the submodule commit
>> +        used on one side of the merge is a descendant of the submodule
>> +        commit used on the other side of the merge, Git attempts to
>> +        fast-forward to the descendant. Otherwise, Git will treat this case
>> +        as a conflict, suggesting as a resolution a submodule commit that
>> +        is descendant of the conflicting ones, if one exists.
>>  +
>>  The 'recursive' strategy takes the same options as 'ort'.  However,
>>  there are three additional options that 'ort' ignores (not documented
>
>
> If both chunks are meant to be kept identical, I would recommend to
> define an attribute (see
> https://docs.asciidoctor.org/asciidoc/latest/attributes/custom-attributes/)
> and use it at both sites.

Wouldn't it be a bit awkward to maintain a six-line paragraph as a custom attribute, though [*1*]? Would the resulting text become like (without indentation) this?

  :submodule-merge: \
  In the case where the path is a submodule, if the submodule commit \
  used on one side of the merge is a descendant of the submodule \
  commit used on the other side of the merge, Git attempts to \
  fast-forward to the descendant. Otherwise, Git will treat this case \
  as a conflict, suggesting as a resolution a submodule commit that \
  is descendant of the conflicting ones, if one exists.
  recursive::
          ...
          the default strategy for resolving two heads from Git v0.99.9k
          until v2.33.0.
  +
  {submodule-merge}
  +
  The 'recursive strategy takes the same options as ...

Just as in C preprocessor macros in *.h files, I am reluctant to force our people to edit long multi-line text while not forgetting to lose the backslash for line continuation (or misplace existing ones when wrapping lines).

And of course a 6-line paragraph is not large enough to put in a separate file to be included.

Hmph...
Thanks.
[Reference]

*1* https://github.com/asciidoctor/asciidoctor/issues/1341#issuecomment-101841014

Lucas Seiki Oshiro· Feb 22, 2025, 19:36 UTC · re: Junio C Hamano · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

> And of course a 6-line paragraph is not large enough to put in a
> separate file to be included.

I'm a newbie here, so I can't have a strong opinion on what's the best solution for managing those files. But, given that:

1. `ort` will sometime replace `recursive`
2. the last change in the content of this document was in
    f5a3c5e637, three years ago, basically copying the content
    from `recursive` to `ort`

it looks like to me that creating another file only for this paragraph would harder to maintain than that duplication.

I mean, if eventually `recursive` is replaced by `ort`, one will need to remember to move this paragraph to `merge-strategies`, as it will be used only in the `ort` documentation. On the other hand, given that this document haven't changed since the introduction of `ort`, this duplication doesn't seem to me that will be hard to be managed.

Anyway, thanks for the feedback!
Junio C Hamano· Feb 22, 2025, 22:17 UTC · re: Lucas Seiki Oshiro · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

Lucas Seiki Oshiro <lucasseikioshiro@gmail.com> writes:
Show 21 quoted lines
>> And of course a 6-line paragraph is not large enough to put in a
>> separate file to be included.
>
> I'm a newbie here, so I can't have a strong opinion on what's
> the best solution for managing those files. But, given that:
>
> 1. `ort` will sometime replace `recursive`
> 2. the last change in the content of this document was in
>    f5a3c5e637, three years ago, basically copying the content
>    from `recursive` to `ort`
>
> it looks like to me that creating another file only for this
> paragraph would harder to maintain than that duplication.
>
> I mean, if eventually `recursive` is replaced by `ort`, one
> will need to remember to move this paragraph to
> `merge-strategies`, as it will be used only in the `ort`
> documentation. On the other hand, given that this document
> haven't changed since the introduction of `ort`, this
> duplication doesn't seem to me that will be hard to be
> managed.

A relatively easy way out would be to have the full warning in the 'ort' section, and then only add only something like

	For a path that is a submodule, the same caution as 'ort'
	applies to this strategy.
to the 'recursive' section.
D. Ben Knoble· Feb 24, 2025, 17:31 UTC · re: Junio C Hamano · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

On Sat, Feb 22, 2025 at 5:18 PM Junio C Hamano <gitster@pobox.com> wrote:
Show 32 quoted lines
>
> Lucas Seiki Oshiro <lucasseikioshiro@gmail.com> writes:
>
> >> And of course a 6-line paragraph is not large enough to put in a
> >> separate file to be included.
> >
> > I'm a newbie here, so I can't have a strong opinion on what's
> > the best solution for managing those files. But, given that:
> >
> > 1. `ort` will sometime replace `recursive`
> > 2. the last change in the content of this document was in
> >    f5a3c5e637, three years ago, basically copying the content
> >    from `recursive` to `ort`
> >
> > it looks like to me that creating another file only for this
> > paragraph would harder to maintain than that duplication.
> >
> > I mean, if eventually `recursive` is replaced by `ort`, one
> > will need to remember to move this paragraph to
> > `merge-strategies`, as it will be used only in the `ort`
> > documentation. On the other hand, given that this document
> > haven't changed since the introduction of `ort`, this
> > duplication doesn't seem to me that will be hard to be
> > managed.
>
> A relatively easy way out would be to have the full warning in the
> 'ort' section, and then only add only something like
>
>         For a path that is a submodule, the same caution as 'ort'
>         applies to this strategy.
>
> to the 'recursive' section.

Indeed, that seems preferable to me (based on a similar conversation about a different documentation change in another project [1]).

[1]: https://github.com/racket/racket/pull/5144#issuecomment-2563172012
-- 
D. Ben Knoble
Elijah Newren· Feb 21, 2025, 21:56 UTC · re: Lucas Seiki Oshiro · lore

Re: [GSoC][PATCH v2] merge-strategies.adoc: detail submodule merge

Hi,

On Thu, Feb 20, 2025 at 7:12 AM Lucas Seiki Oshiro <lucasseikioshiro@gmail.com> wrote:

Show 65 quoted lines
>
> Submodule merges are, in general, similar to other merges based on oid
> three-way-merge. When a conflict happens, however, Git has two special
> cases (introduced in 68d03e4a6e44) on handling the conflict before
> yielding it to the user. From the merge-ort and merge-recursive sources:
>
> - "Case #1: a is contained in b or vice versa": both strategies try to
> perform a fast-forward in the submodules if the commit referred by the
> conflicted submodule is descendant of another;
>
> - "Case #2: There are one or more merges that contain a and b in the
> submodule.  If there is only one, then present it as a suggestion to the
> user, but leave it marked unmerged so the user needs to confirm the
> resolution."
>
> Add a small paragraph on merge-strategies.adoc describing this behavior.
>
> Helped-by: Elijah Newren <newren@gmail.com>
> Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
> ---
>
> This v2 changes the documentation text to a clearer explanation (as
> suggested in the v1 review), and changes its location to
> merge-strategies.adoc instead of git-merge.adoc.
>
> This content is duplicated as this works for both `ort` and `recursive`
> strategies.
>
>  Documentation/merge-strategies.adoc | 15 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/Documentation/merge-strategies.adoc b/Documentation/merge-strategies.adoc
> index 5fc54ec060..a7fca249e2 100644
> --- a/Documentation/merge-strategies.adoc
> +++ b/Documentation/merge-strategies.adoc
> @@ -21,6 +21,13 @@ ort::
>         ("Ostensibly Recursive's Twin") and came from the fact that it
>         was written as a replacement for the previous default
>         algorithm, `recursive`.
> +
> +        In the case where the path is a submodule, if the submodule commit
> +        used on one side of the merge is a descendant of the submodule
> +        commit used on the other side of the merge, Git attempts to
> +        fast-forward to the descendant. Otherwise, Git will treat this case
> +        as a conflict, suggesting as a resolution a submodule commit that
> +        is descendant of the conflicting ones, if one exists.
>  +
>  The 'ort' strategy can take the following options:
>
> @@ -95,6 +102,13 @@ recursive::
>         renames.  It does not make use of detected copies.  This was
>         the default strategy for resolving two heads from Git v0.99.9k
>         until v2.33.0.
> +
> +        In the case where the path is a submodule, if the submodule commit
> +        used on one side of the merge is a descendant of the submodule
> +        commit used on the other side of the merge, Git attempts to
> +        fast-forward to the descendant. Otherwise, Git will treat this case
> +        as a conflict, suggesting as a resolution a submodule commit that
> +        is descendant of the conflicting ones, if one exists.
>  +
>  The 'recursive' strategy takes the same options as 'ort'.  However,
>  there are three additional options that 'ort' ignores (not documented
> --
> 2.39.5 (Apple Git-154)

So, seeing it here, I note that these are meant a bit more as high-level overviews of the algorithms. I pushed you away from including this in git-merge.adoc because while that manual page does dive into merge resolution details, that manual page is specific to merge. The information here pertains to merge as well as cherry-pick, rebase, revert, replay, merge-tree, etc.

We don't seem to have a place that is general for all merge-machinery-using commands, and which also dives into details about how merges are resolved.

I don't have a good solution. I think it's probably fine to include here in merge-strategies.adoc, even if it feels suboptimal and icky, since any other current solution would be as well. But I would be interested in the opinions of other reviewers on this point and whether they see a good solution (short of completely overhauling all merge-related documentation for any merge-using-command, which might be a viable strategy but shouldn't hold up a small patch like this).

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