[PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[Taylor Blau]

In the previous commit, we introduced '--split=<no-merge|merge-all>',
and alluded to the fact that '--split=merge-all' would be useful for
callers who wish to always trigger a merge of an incremental chain.

There is a problem with the above approach, which is that there is no
way to specify to the commit-graph builtin that a caller only wants to
include commits already in the graph. One can specify '--input=append'
to include all commits in the existing graphs, but the absence of
'--input=stdin-{commits,packs}' causes the builtin to call
'fill_oids_from_all_packs()'.

Passing '--input=reachable' (as in 'git commit-graph write
--split=merge-all --input=reachable --input=append') works around this
issue by making '--input=reachable' effectively a no-op, but this can be
prohibitively expensive in large repositories, making it an undesirable
choice for some users.

Teach '--input=none' as an option to behave as if '--input=append' were
given, but to consider no other sources in addition.

This, in conjunction with the option introduced in the previous patch
offers the convenient way to force the commit-graph machinery to
condense a chain of incrementals without requiring any new commits:

  $ git commit-graph write --split=merge-all --input=none

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 Documentation/git-commit-graph.txt |  8 +++++++-
 builtin/commit-graph.c             | 11 ++++++++---
 commit-graph.c                     |  6 ++++--
 commit-graph.h                     |  3 ++-
 t/t5324-split-commit-graph.sh      | 26 ++++++++++++++++++++++++++
 5 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 0a320cccdd..b210cef52f 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -39,7 +39,7 @@ COMMANDS
 --------
 'write'::
 
-Write a commit-graph file based on the commits found in packfiles.
+Write a commit-graph file based on the specified sources of input:
 +
 With the `--input=stdin-packs` option, generate the new commit graph by
 walking objects only in the specified pack-indexes. (Cannot be combined
@@ -57,6 +57,12 @@ walking commits starting at all refs. (Cannot be combined with
 With the `--input=append` option, include all commits that are present
 in the existing commit-graph file.
 +
+With the `--input=none` option, behave as if `--input=append` were
+given, but do not walk other packs to find additional commits.
++
+If none of the above options are given, then generate the new
+commit-graph by walking over all pack-indexes.
++
 With the `--split[=<strategy>]` option, write the commit-graph as a
 chain of multiple commit-graph files stored in
 `<dir>/info/commit-graphs`. Commit-graph layers are merged based on the
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 0ff25896d0..a71af88815 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -11,7 +11,7 @@ static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
 	N_("git commit-graph write [--object-dir <objdir>] "
 	   "[--split[=<strategy>]] "
-	   "[--input=<reachable|stdin-packs|stdin-commits|append>] "
+	   "[--input=<reachable|stdin-packs|stdin-commits|append|none>] "
 	   "[--[no-]progress] <split options>"),
 	NULL
 };
@@ -24,7 +24,7 @@ static const char * const builtin_commit_graph_verify_usage[] = {
 static const char * const builtin_commit_graph_write_usage[] = {
 	N_("git commit-graph write [--object-dir <objdir>] "
 	   "[--split[=<strategy>]] "
-	   "[--input=<reachable|stdin-packs|stdin-commits|append>] "
+	   "[--input=<reachable|stdin-packs|stdin-commits|append|none>] "
 	   "[--[no-]progress] <split options>"),
 	NULL
 };
@@ -33,7 +33,8 @@ enum commit_graph_input {
 	COMMIT_GRAPH_INPUT_REACHABLE     = (1 << 1),
 	COMMIT_GRAPH_INPUT_STDIN_PACKS   = (1 << 2),
 	COMMIT_GRAPH_INPUT_STDIN_COMMITS = (1 << 3),
-	COMMIT_GRAPH_INPUT_APPEND        = (1 << 4)
+	COMMIT_GRAPH_INPUT_APPEND        = (1 << 4),
+	COMMIT_GRAPH_INPUT_NONE          = (1 << 5)
 };
 
 static struct opts_commit_graph {
@@ -80,6 +81,8 @@ static int option_parse_input(const struct option *opt, const char *arg,
 		*to |= COMMIT_GRAPH_INPUT_STDIN_COMMITS;
 	else if (!strcmp(arg, "append"))
 		*to |= COMMIT_GRAPH_INPUT_APPEND;
+	else if (!strcmp(arg, "none"))
+		*to |= (COMMIT_GRAPH_INPUT_APPEND | COMMIT_GRAPH_INPUT_NONE);
 	else
 		die(_("unrecognized --input source, %s"), arg);
 	return 0;
@@ -225,6 +228,8 @@ static int graph_write(int argc, const char **argv)
 		opts.obj_dir = get_object_directory();
 	if (opts.input & COMMIT_GRAPH_INPUT_APPEND)
 		flags |= COMMIT_GRAPH_WRITE_APPEND;
+	if (opts.input & COMMIT_GRAPH_INPUT_NONE)
+		flags |= COMMIT_GRAPH_WRITE_NO_INPUT;
 	if (opts.split)
 		flags |= COMMIT_GRAPH_WRITE_SPLIT;
 	if (opts.progress)
diff --git a/commit-graph.c b/commit-graph.c
index 3a5cb23cd7..417b7eac9c 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -788,7 +788,8 @@ struct write_commit_graph_context {
 	unsigned append:1,
 		 report_progress:1,
 		 split:1,
-		 check_oids:1;
+		 check_oids:1,
+		 no_input:1;
 
 	const struct split_commit_graph_opts *split_opts;
 };
@@ -1785,6 +1786,7 @@ int write_commit_graph(struct object_directory *odb,
 	ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0;
 	ctx->check_oids = flags & COMMIT_GRAPH_WRITE_CHECK_OIDS ? 1 : 0;
 	ctx->split_opts = split_opts;
+	ctx->no_input = flags & COMMIT_GRAPH_WRITE_NO_INPUT ? 1 : 0;
 
 	if (ctx->split) {
 		struct commit_graph *g;
@@ -1843,7 +1845,7 @@ int write_commit_graph(struct object_directory *odb,
 			goto cleanup;
 	}
 
-	if (!pack_indexes && !commit_hex)
+	if (!ctx->no_input && !pack_indexes && !commit_hex)
 		fill_oids_from_all_packs(ctx);
 
 	close_reachable(ctx);
diff --git a/commit-graph.h b/commit-graph.h
index 65a7d2edae..df7f3f5961 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -79,7 +79,8 @@ enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_PROGRESS   = (1 << 1),
 	COMMIT_GRAPH_WRITE_SPLIT      = (1 << 2),
 	/* Make sure that each OID in the input is a valid commit OID. */
-	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3)
+	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3),
+	COMMIT_GRAPH_WRITE_NO_INPUT   = (1 << 4)
 };
 
 enum commit_graph_split_flags {
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 6894106727..7614f3915b 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -376,4 +376,30 @@ test_expect_success '--split=no-merge always writes an incremental' '
 	test_line_count = 2 $graphdir/commit-graph-chain
 '
 
+test_expect_success '--split=no-merge, --input=none writes nothing' '
+	test_when_finished rm -rf a graphs.before graphs.after &&
+	rm -rf $graphdir &&
+	git reset --hard commits/2 &&
+	git rev-list -1 HEAD~1 >a &&
+	git commit-graph write --split=no-merge --input=stdin-commits <a &&
+	ls $graphdir/graph-*.graph >graphs.before &&
+	test_line_count = 1 $graphdir/commit-graph-chain &&
+	git commit-graph write --split --input=none &&
+	ls $graphdir/graph-*.graph >graphs.after &&
+	test_cmp graphs.before graphs.after
+'
+
+test_expect_success '--split=merge-all, --input=none merges the chain' '
+	test_when_finished rm -rf a b &&
+	rm -rf $graphdir &&
+	git reset --hard commits/2 &&
+	git rev-list -1 HEAD~1 >a &&
+	git rev-list -1 HEAD >b &&
+	git commit-graph write --split=no-merge --input=stdin-commits <a &&
+	git commit-graph write --split=no-merge --input=stdin-commits <b &&
+	test_line_count = 2 $graphdir/commit-graph-chain &&
+	git commit-graph write --split=merge-all --input=none &&
+	test_line_count = 1 $graphdir/commit-graph-chain
+'
+
 test_done
-- 
2.25.0.119.gaa12b7378b

Re: [PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[SZEDER Gábor]

On Tue, Feb 11, 2020 at 09:47:57PM -0800, Taylor Blau wrote:
> In the previous commit, we introduced '--split=<no-merge|merge-all>',

Nit: the previous commit introduced '--input=<source>'.

> and alluded to the fact that '--split=merge-all' would be useful for
> callers who wish to always trigger a merge of an incremental chain.

Re: [PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[SZEDER Gábor]

On Tue, Feb 11, 2020 at 09:47:57PM -0800, Taylor Blau wrote:
> In the previous commit, we introduced '--split=<no-merge|merge-all>',
> and alluded to the fact that '--split=merge-all' would be useful for
> callers who wish to always trigger a merge of an incremental chain.
> 
> There is a problem with the above approach, which is that there is no
> way to specify to the commit-graph builtin that a caller only wants to
> include commits already in the graph.

I'd like clarification on a detail here.  Is it only about not adding
any new commits, or about keeping all existing commits as well?  IOW,
do you want to:

  - include only commits already existing in the commit-graph, without
    adding any new commits, but remove any commits that do not exist
    in the object database anymore.

or:

  - include _all_ commits already existing in the commit-graph, even
    those that don't exist anymore in the object database, without
    adding any new commits.

Re: [PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[Junio C Hamano]

SZEDER Gábor <szeder.dev@gmail.com> writes:

> On Tue, Feb 11, 2020 at 09:47:57PM -0800, Taylor Blau wrote:
>> In the previous commit, we introduced '--split=<no-merge|merge-all>',
>> and alluded to the fact that '--split=merge-all' would be useful for
>> callers who wish to always trigger a merge of an incremental chain.
>> 
>> There is a problem with the above approach, which is that there is no
>> way to specify to the commit-graph builtin that a caller only wants to
>> include commits already in the graph.
>
> I'd like clarification on a detail here.  Is it only about not adding
> any new commits, or about keeping all existing commits as well?  IOW,
> do you want to:
>
>   - include only commits already existing in the commit-graph, without
>     adding any new commits, but remove any commits that do not exist
>     in the object database anymore.
>
> or:
>
>   - include _all_ commits already existing in the commit-graph, even
>     those that don't exist anymore in the object database, without
>     adding any new commits.

FWIW, I read it as the former, but now you brought it up, it can be
read either way.

Thanks for good review comments, as always.

Re: [PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[Taylor Blau]

On Thu, Feb 13, 2020 at 01:31:29PM +0100, SZEDER Gábor wrote:
> On Tue, Feb 11, 2020 at 09:47:57PM -0800, Taylor Blau wrote:
> > In the previous commit, we introduced '--split=<no-merge|merge-all>',
> > and alluded to the fact that '--split=merge-all' would be useful for
> > callers who wish to always trigger a merge of an incremental chain.
> >
> > There is a problem with the above approach, which is that there is no
> > way to specify to the commit-graph builtin that a caller only wants to
> > include commits already in the graph.
>
> I'd like clarification on a detail here.  Is it only about not adding
> any new commits, or about keeping all existing commits as well?  IOW,
> do you want to:
>
>   - include only commits already existing in the commit-graph, without
>     adding any new commits, but remove any commits that do not exist
>     in the object database anymore.

This one, since the commit-graph machinery will drop any commits (no
matter what input/source/mode you specify) that no longer exist in the
object store.

> or:
>
>   - include _all_ commits already existing in the commit-graph, even
>     those that don't exist anymore in the object database, without
>     adding any new commits.

Thanks,
Taylor

Re: [PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[Taylor Blau]

On Thu, Feb 13, 2020 at 08:08:15AM -0800, Junio C Hamano wrote:
> SZEDER Gábor <szeder.dev@gmail.com> writes:
>
> > On Tue, Feb 11, 2020 at 09:47:57PM -0800, Taylor Blau wrote:
> >> In the previous commit, we introduced '--split=<no-merge|merge-all>',
> >> and alluded to the fact that '--split=merge-all' would be useful for
> >> callers who wish to always trigger a merge of an incremental chain.
> >>
> >> There is a problem with the above approach, which is that there is no
> >> way to specify to the commit-graph builtin that a caller only wants to
> >> include commits already in the graph.
> >
> > I'd like clarification on a detail here.  Is it only about not adding
> > any new commits, or about keeping all existing commits as well?  IOW,
> > do you want to:
> >
> >   - include only commits already existing in the commit-graph, without
> >     adding any new commits, but remove any commits that do not exist
> >     in the object database anymore.
> >
> > or:
> >
> >   - include _all_ commits already existing in the commit-graph, even
> >     those that don't exist anymore in the object database, without
> >     adding any new commits.
>
> FWIW, I read it as the former, but now you brought it up, it can be
> read either way.

It was intended as the former, but I share both of your feelings that it
could be read either way. I amended the commit message to clarify by
adding:

  (and haven't since been deleted from the object store)

as a parenthetical after "already in the graph...".

> Thanks for good review comments, as always.

Yes, indeed: thank very much for your thoughtful feedback.

Thanks,
Taylor

[PATCH v3 3/3] builtin/commit-graph.c: support '--input=none'

[Taylor Blau]

In the previous commit, we introduced '--split=<no-merge|merge-all>',
and alluded to the fact that '--split=merge-all' would be useful for
callers who wish to always trigger a merge of an incremental chain.

There is a problem with the above approach, which is that there is no
way to specify to the commit-graph builtin that a caller only wants to
include commits already in the graph. One can specify '--input=append'
to include all commits in the existing graphs (that haven't since been
deleted from the object store), but the absence of
'--input=stdin-{commits,packs}' causes the builtin to call
'fill_oids_from_all_packs()'.

Passing '--input=reachable' (as in 'git commit-graph write
--split=merge-all --input=reachable --input=append') works around this
issue by making '--input=reachable' effectively a no-op, but this can be
prohibitively expensive in large repositories, making it an undesirable
choice for some users.

Teach '--input=none' as an option to behave as if '--input=append' were
given, but to consider no other sources in addition.

This, in conjunction with the option introduced in the previous patch
offers the convenient way to force the commit-graph machinery to
condense a chain of incrementals without requiring any new commits:

  $ git commit-graph write --split=merge-all --input=none

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 Documentation/git-commit-graph.txt |  8 +++++++-
 builtin/commit-graph.c             | 11 ++++++++---
 commit-graph.c                     |  6 ++++--
 commit-graph.h                     |  3 ++-
 t/t5324-split-commit-graph.sh      | 26 ++++++++++++++++++++++++++
 5 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 0a320cccdd..b210cef52f 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -39,7 +39,7 @@ COMMANDS
 --------
 'write'::

-Write a commit-graph file based on the commits found in packfiles.
+Write a commit-graph file based on the specified sources of input:
 +
 With the `--input=stdin-packs` option, generate the new commit graph by
 walking objects only in the specified pack-indexes. (Cannot be combined
@@ -57,6 +57,12 @@ walking commits starting at all refs. (Cannot be combined with
 With the `--input=append` option, include all commits that are present
 in the existing commit-graph file.
 +
+With the `--input=none` option, behave as if `--input=append` were
+given, but do not walk other packs to find additional commits.
++
+If none of the above options are given, then generate the new
+commit-graph by walking over all pack-indexes.
++
 With the `--split[=<strategy>]` option, write the commit-graph as a
 chain of multiple commit-graph files stored in
 `<dir>/info/commit-graphs`. Commit-graph layers are merged based on the
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 0ff25896d0..a71af88815 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -11,7 +11,7 @@ static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
 	N_("git commit-graph write [--object-dir <objdir>] "
 	   "[--split[=<strategy>]] "
-	   "[--input=<reachable|stdin-packs|stdin-commits|append>] "
+	   "[--input=<reachable|stdin-packs|stdin-commits|append|none>] "
 	   "[--[no-]progress] <split options>"),
 	NULL
 };
@@ -24,7 +24,7 @@ static const char * const builtin_commit_graph_verify_usage[] = {
 static const char * const builtin_commit_graph_write_usage[] = {
 	N_("git commit-graph write [--object-dir <objdir>] "
 	   "[--split[=<strategy>]] "
-	   "[--input=<reachable|stdin-packs|stdin-commits|append>] "
+	   "[--input=<reachable|stdin-packs|stdin-commits|append|none>] "
 	   "[--[no-]progress] <split options>"),
 	NULL
 };
@@ -33,7 +33,8 @@ enum commit_graph_input {
 	COMMIT_GRAPH_INPUT_REACHABLE     = (1 << 1),
 	COMMIT_GRAPH_INPUT_STDIN_PACKS   = (1 << 2),
 	COMMIT_GRAPH_INPUT_STDIN_COMMITS = (1 << 3),
-	COMMIT_GRAPH_INPUT_APPEND        = (1 << 4)
+	COMMIT_GRAPH_INPUT_APPEND        = (1 << 4),
+	COMMIT_GRAPH_INPUT_NONE          = (1 << 5)
 };

 static struct opts_commit_graph {
@@ -80,6 +81,8 @@ static int option_parse_input(const struct option *opt, const char *arg,
 		*to |= COMMIT_GRAPH_INPUT_STDIN_COMMITS;
 	else if (!strcmp(arg, "append"))
 		*to |= COMMIT_GRAPH_INPUT_APPEND;
+	else if (!strcmp(arg, "none"))
+		*to |= (COMMIT_GRAPH_INPUT_APPEND | COMMIT_GRAPH_INPUT_NONE);
 	else
 		die(_("unrecognized --input source, %s"), arg);
 	return 0;
@@ -225,6 +228,8 @@ static int graph_write(int argc, const char **argv)
 		opts.obj_dir = get_object_directory();
 	if (opts.input & COMMIT_GRAPH_INPUT_APPEND)
 		flags |= COMMIT_GRAPH_WRITE_APPEND;
+	if (opts.input & COMMIT_GRAPH_INPUT_NONE)
+		flags |= COMMIT_GRAPH_WRITE_NO_INPUT;
 	if (opts.split)
 		flags |= COMMIT_GRAPH_WRITE_SPLIT;
 	if (opts.progress)
diff --git a/commit-graph.c b/commit-graph.c
index 3a5cb23cd7..417b7eac9c 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -788,7 +788,8 @@ struct write_commit_graph_context {
 	unsigned append:1,
 		 report_progress:1,
 		 split:1,
-		 check_oids:1;
+		 check_oids:1,
+		 no_input:1;

 	const struct split_commit_graph_opts *split_opts;
 };
@@ -1785,6 +1786,7 @@ int write_commit_graph(struct object_directory *odb,
 	ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0;
 	ctx->check_oids = flags & COMMIT_GRAPH_WRITE_CHECK_OIDS ? 1 : 0;
 	ctx->split_opts = split_opts;
+	ctx->no_input = flags & COMMIT_GRAPH_WRITE_NO_INPUT ? 1 : 0;

 	if (ctx->split) {
 		struct commit_graph *g;
@@ -1843,7 +1845,7 @@ int write_commit_graph(struct object_directory *odb,
 			goto cleanup;
 	}

-	if (!pack_indexes && !commit_hex)
+	if (!ctx->no_input && !pack_indexes && !commit_hex)
 		fill_oids_from_all_packs(ctx);

 	close_reachable(ctx);
diff --git a/commit-graph.h b/commit-graph.h
index 65a7d2edae..df7f3f5961 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -79,7 +79,8 @@ enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_PROGRESS   = (1 << 1),
 	COMMIT_GRAPH_WRITE_SPLIT      = (1 << 2),
 	/* Make sure that each OID in the input is a valid commit OID. */
-	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3)
+	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3),
+	COMMIT_GRAPH_WRITE_NO_INPUT   = (1 << 4)
 };

 enum commit_graph_split_flags {
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 6894106727..7614f3915b 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -376,4 +376,30 @@ test_expect_success '--split=no-merge always writes an incremental' '
 	test_line_count = 2 $graphdir/commit-graph-chain
 '

+test_expect_success '--split=no-merge, --input=none writes nothing' '
+	test_when_finished rm -rf a graphs.before graphs.after &&
+	rm -rf $graphdir &&
+	git reset --hard commits/2 &&
+	git rev-list -1 HEAD~1 >a &&
+	git commit-graph write --split=no-merge --input=stdin-commits <a &&
+	ls $graphdir/graph-*.graph >graphs.before &&
+	test_line_count = 1 $graphdir/commit-graph-chain &&
+	git commit-graph write --split --input=none &&
+	ls $graphdir/graph-*.graph >graphs.after &&
+	test_cmp graphs.before graphs.after
+'
+
+test_expect_success '--split=merge-all, --input=none merges the chain' '
+	test_when_finished rm -rf a b &&
+	rm -rf $graphdir &&
+	git reset --hard commits/2 &&
+	git rev-list -1 HEAD~1 >a &&
+	git rev-list -1 HEAD >b &&
+	git commit-graph write --split=no-merge --input=stdin-commits <a &&
+	git commit-graph write --split=no-merge --input=stdin-commits <b &&
+	test_line_count = 2 $graphdir/commit-graph-chain &&
+	git commit-graph write --split=merge-all --input=none &&
+	test_line_count = 1 $graphdir/commit-graph-chain
+'
+
 test_done
--
2.24.1.2723.g1e7b7fcc88

[PATCH v4] builtin/commit-graph.c: support '--input=graphed'

[Taylor Blau]

Hi,

In response to some discussion in [1], here is another idea instead of
'--input=none' that may make things a little clearer. Since it had been
a long time, I reminded myself that '--input=none' means
"--input=append, but don't look at packs as is usually the default".

In [1], Gabor suggested that we could call this '--input=exists' or
'--input=existing', but I think that 'graphed' may be clearer, since
it is closer to "only _graphed_ commits".

Another option would be to call this '--input=only-graphed', but I think
that may be overly verbose for what we're going for here.

Let me know what you think.

[1]: https://lore.kernel.org/git/20200322110424.GC2224@szeder.dev/

--- 8< ---

In the previous commit, we introduced '--split=<no-merge|merge-all>',
and alluded to the fact that '--split=merge-all' would be useful for
callers who wish to always trigger a merge of an incremental chain.

There is a problem with the above approach, which is that there is no
way to specify to the commit-graph builtin that a caller only wants to
include commits already in the graph. One can specify '--input=append'
to include all commits in the existing graphs, but the absence of
'--input=stdin-{commits,packs}' causes the builtin to call
'fill_oids_from_all_packs()'.

Passing '--input=reachable' (as in 'git commit-graph write
--split=merge-all --input=reachable --input=append') works around this
issue by making '--input=reachable' effectively a no-op, but this can be
prohibitively expensive in large repositories, making it an undesirable
choice for some users.

Teach '--input=graphed' as an option to behave as if '--input=append' were
given, but to consider no other sources in addition.

This, in conjunction with the option introduced in the previous patch
offers the convenient way to force the commit-graph machinery to
condense a chain of incrementals without requiring any new commits:

  $ git commit-graph write --split=merge-all --input=graphed

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 Documentation/git-commit-graph.txt |  8 +++++++-
 builtin/commit-graph.c             | 11 ++++++++---
 commit-graph.c                     |  6 ++++--
 commit-graph.h                     |  3 ++-
 t/t5324-split-commit-graph.sh      | 26 ++++++++++++++++++++++++++
 5 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 0a320cccdd..4d8fbbe8ff 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -39,7 +39,7 @@ COMMANDS
 --------
 'write'::

-Write a commit-graph file based on the commits found in packfiles.
+Write a commit-graph file based on the specified sources of input:
 +
 With the `--input=stdin-packs` option, generate the new commit graph by
 walking objects only in the specified pack-indexes. (Cannot be combined
@@ -57,6 +57,12 @@ walking commits starting at all refs. (Cannot be combined with
 With the `--input=append` option, include all commits that are present
 in the existing commit-graph file.
 +
+With the `--input=graphed` option, behave as if `--input=append` were
+given, but do not walk other packs to find additional commits.
++
+If none of the above options are given, then generate the new
+commit-graph by walking over all pack-indexes.
++
 With the `--split[=<strategy>]` option, write the commit-graph as a
 chain of multiple commit-graph files stored in
 `<dir>/info/commit-graphs`. Commit-graph layers are merged based on the
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 0ff25896d0..dfb6c554ac 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -11,7 +11,7 @@ static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
 	N_("git commit-graph write [--object-dir <objdir>] "
 	   "[--split[=<strategy>]] "
-	   "[--input=<reachable|stdin-packs|stdin-commits|append>] "
+	   "[--input=<reachable|stdin-packs|stdin-commits|append|graphed>] "
 	   "[--[no-]progress] <split options>"),
 	NULL
 };
@@ -24,7 +24,7 @@ static const char * const builtin_commit_graph_verify_usage[] = {
 static const char * const builtin_commit_graph_write_usage[] = {
 	N_("git commit-graph write [--object-dir <objdir>] "
 	   "[--split[=<strategy>]] "
-	   "[--input=<reachable|stdin-packs|stdin-commits|append>] "
+	   "[--input=<reachable|stdin-packs|stdin-commits|append|graphed>] "
 	   "[--[no-]progress] <split options>"),
 	NULL
 };
@@ -33,7 +33,8 @@ enum commit_graph_input {
 	COMMIT_GRAPH_INPUT_REACHABLE     = (1 << 1),
 	COMMIT_GRAPH_INPUT_STDIN_PACKS   = (1 << 2),
 	COMMIT_GRAPH_INPUT_STDIN_COMMITS = (1 << 3),
-	COMMIT_GRAPH_INPUT_APPEND        = (1 << 4)
+	COMMIT_GRAPH_INPUT_APPEND        = (1 << 4),
+	COMMIT_GRAPH_INPUT_GRAPHED       = (1 << 5)
 };

 static struct opts_commit_graph {
@@ -80,6 +81,8 @@ static int option_parse_input(const struct option *opt, const char *arg,
 		*to |= COMMIT_GRAPH_INPUT_STDIN_COMMITS;
 	else if (!strcmp(arg, "append"))
 		*to |= COMMIT_GRAPH_INPUT_APPEND;
+	else if (!strcmp(arg, "graphed"))
+		*to |= (COMMIT_GRAPH_INPUT_APPEND | COMMIT_GRAPH_INPUT_GRAPHED);
 	else
 		die(_("unrecognized --input source, %s"), arg);
 	return 0;
@@ -225,6 +228,8 @@ static int graph_write(int argc, const char **argv)
 		opts.obj_dir = get_object_directory();
 	if (opts.input & COMMIT_GRAPH_INPUT_APPEND)
 		flags |= COMMIT_GRAPH_WRITE_APPEND;
+	if (opts.input & COMMIT_GRAPH_INPUT_GRAPHED)
+		flags |= COMMIT_GRAPH_WRITE_NO_INPUT;
 	if (opts.split)
 		flags |= COMMIT_GRAPH_WRITE_SPLIT;
 	if (opts.progress)
diff --git a/commit-graph.c b/commit-graph.c
index c5a8ea244b..3da52847e4 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -788,7 +788,8 @@ struct write_commit_graph_context {
 	unsigned append:1,
 		 report_progress:1,
 		 split:1,
-		 check_oids:1;
+		 check_oids:1,
+		 no_input:1;

 	const struct split_commit_graph_opts *split_opts;
 };
@@ -1781,6 +1782,7 @@ int write_commit_graph(struct object_directory *odb,
 	ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0;
 	ctx->check_oids = flags & COMMIT_GRAPH_WRITE_CHECK_OIDS ? 1 : 0;
 	ctx->split_opts = split_opts;
+	ctx->no_input = flags & COMMIT_GRAPH_WRITE_NO_INPUT ? 1 : 0;

 	if (ctx->split) {
 		struct commit_graph *g;
@@ -1839,7 +1841,7 @@ int write_commit_graph(struct object_directory *odb,
 			goto cleanup;
 	}

-	if (!pack_indexes && !commit_hex)
+	if (!ctx->no_input && !pack_indexes && !commit_hex)
 		fill_oids_from_all_packs(ctx);

 	close_reachable(ctx);
diff --git a/commit-graph.h b/commit-graph.h
index 65a7d2edae..df7f3f5961 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -79,7 +79,8 @@ enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_PROGRESS   = (1 << 1),
 	COMMIT_GRAPH_WRITE_SPLIT      = (1 << 2),
 	/* Make sure that each OID in the input is a valid commit OID. */
-	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3)
+	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3),
+	COMMIT_GRAPH_WRITE_NO_INPUT   = (1 << 4)
 };

 enum commit_graph_split_flags {
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 6894106727..6dda4c1f1c 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -376,4 +376,30 @@ test_expect_success '--split=no-merge always writes an incremental' '
 	test_line_count = 2 $graphdir/commit-graph-chain
 '

+test_expect_success '--split=no-merge, --input=graphed writes nothing' '
+	test_when_finished rm -rf a graphs.before graphs.after &&
+	rm -rf $graphdir &&
+	git reset --hard commits/2 &&
+	git rev-list -1 HEAD~1 >a &&
+	git commit-graph write --split=no-merge --input=stdin-commits <a &&
+	ls $graphdir/graph-*.graph >graphs.before &&
+	test_line_count = 1 $graphdir/commit-graph-chain &&
+	git commit-graph write --split --input=graphed &&
+	ls $graphdir/graph-*.graph >graphs.after &&
+	test_cmp graphs.before graphs.after
+'
+
+test_expect_success '--split=merge-all, --input=graphed merges the chain' '
+	test_when_finished rm -rf a b &&
+	rm -rf $graphdir &&
+	git reset --hard commits/2 &&
+	git rev-list -1 HEAD~1 >a &&
+	git rev-list -1 HEAD >b &&
+	git commit-graph write --split=no-merge --input=stdin-commits <a &&
+	git commit-graph write --split=no-merge --input=stdin-commits <b &&
+	test_line_count = 2 $graphdir/commit-graph-chain &&
+	git commit-graph write --split=merge-all --input=graphed &&
+	test_line_count = 1 $graphdir/commit-graph-chain
+'
+
 test_done
--
2.26.0.rc2.311.g2e49f7a131

Re: [PATCH v4] builtin/commit-graph.c: support '--input=graphed'

[Jeff King]

On Mon, Mar 23, 2020 at 02:12:19PM -0600, Taylor Blau wrote:

> Hi,
> 
> In response to some discussion in [1], here is another idea instead of
> '--input=none' that may make things a little clearer. Since it had been
> a long time, I reminded myself that '--input=none' means
> "--input=append, but don't look at packs as is usually the default".
> 
> In [1], Gabor suggested that we could call this '--input=exists' or
> '--input=existing', but I think that 'graphed' may be clearer, since
> it is closer to "only _graphed_ commits".

Yeah, this name is much more clear to me than "none" (and would have
prevented some mild confusion I had when experimenting the other day).

> Another option would be to call this '--input=only-graphed', but I think
> that may be overly verbose for what we're going for here.

Agreed.

-Peff

Re: [PATCH v4] builtin/commit-graph.c: support '--input=graphed'

[SZEDER Gábor]

On Mon, Mar 23, 2020 at 02:12:19PM -0600, Taylor Blau wrote:
> Hi,
> 
> In response to some discussion in [1], here is another idea instead of
> '--input=none' that may make things a little clearer. Since it had been
> a long time, I reminded myself that '--input=none' means
> "--input=append, but don't look at packs as is usually the default".
> 
> In [1], Gabor suggested that we could call this '--input=exists' or
> '--input=existing', but I think that 'graphed' may be clearer, since
> it is closer to "only _graphed_ commits".
> 
> Another option would be to call this '--input=only-graphed', but I think
> that may be overly verbose for what we're going for here.
> 
> Let me know what you think.
> 
> [1]: https://lore.kernel.org/git/20200322110424.GC2224@szeder.dev/
> 
> --- 8< ---
> 
> In the previous commit, we introduced '--split=<no-merge|merge-all>',
> and alluded to the fact that '--split=merge-all' would be useful for
> callers who wish to always trigger a merge of an incremental chain.
> 
> There is a problem with the above approach, which is that there is no
> way to specify to the commit-graph builtin that a caller only wants to
> include commits already in the graph. One can specify '--input=append'
> to include all commits in the existing graphs, but the absence of
> '--input=stdin-{commits,packs}' causes the builtin to call
> 'fill_oids_from_all_packs()'.
> 
> Passing '--input=reachable' (as in 'git commit-graph write
> --split=merge-all --input=reachable --input=append') works around this
> issue by making '--input=reachable' effectively a no-op, but this can be
> prohibitively expensive in large repositories, making it an undesirable
> choice for some users.
> 
> Teach '--input=graphed' as an option to behave as if '--input=append' were
> given, but to consider no other sources in addition.
> 
> This, in conjunction with the option introduced in the previous patch
> offers the convenient way to force the commit-graph machinery to
> condense a chain of incrementals without requiring any new commits:
> 
>   $ git commit-graph write --split=merge-all --input=graphed
> 
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---
>  Documentation/git-commit-graph.txt |  8 +++++++-
>  builtin/commit-graph.c             | 11 ++++++++---
>  commit-graph.c                     |  6 ++++--
>  commit-graph.h                     |  3 ++-
>  t/t5324-split-commit-graph.sh      | 26 ++++++++++++++++++++++++++
>  5 files changed, 47 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
> index 0a320cccdd..4d8fbbe8ff 100644
> --- a/Documentation/git-commit-graph.txt
> +++ b/Documentation/git-commit-graph.txt
> @@ -39,7 +39,7 @@ COMMANDS
>  --------
>  'write'::
> 
> -Write a commit-graph file based on the commits found in packfiles.
> +Write a commit-graph file based on the specified sources of input:
>  +
>  With the `--input=stdin-packs` option, generate the new commit graph by
>  walking objects only in the specified pack-indexes. (Cannot be combined
> @@ -57,6 +57,12 @@ walking commits starting at all refs. (Cannot be combined with
>  With the `--input=append` option, include all commits that are present
>  in the existing commit-graph file.
>  +
> +With the `--input=graphed` option, behave as if `--input=append` were
> +given, but do not walk other packs to find additional commits.

s/walk/scan/ would be more fitting, I think.

In an earlier version of these patches I asked for clarification about
what happens with expired commits that are still included in the
commit-graph... and I do remember that you replied to that, but,
unfortunately, not what your reply was.  And after reading this log
message and the documentation update it's still not clear to me.

> ++
> +If none of the above options are given, then generate the new
> +commit-graph by walking over all pack-indexes.

s/walking/scanning/

> ++
>  With the `--split[=<strategy>]` option, write the commit-graph as a
>  chain of multiple commit-graph files stored in
>  `<dir>/info/commit-graphs`. Commit-graph layers are merged based on the