threads / patch / 55134

patcht1500: ensure current --since= behavior remains

Subject: [PATCH] t1500: ensure current --since= behavior remains

## tl;dr

3 messages between Feb 10, 2021 and Feb 11, 2021. Diffs are folded; open one to read it.

replies: 2people: 2as markdown or json

Eric Wong· Feb 10, 2021, 21:55 UTC · lore

This behavior of git-rev-parse is observed since git 1.8.3.1 at least(*), and likely earlier versions.

At least one git-reliant project in-the-wild relies on this current behavior of git-rev-parse being able to handle multiple --since= arguments without squeezing identical results together. So add a test to prevent the potential for regression in downstream projects.

(*) 1.8.3.1 the version packaged for CentOS 7.x

Signed-off-by: Eric Wong <e@80x24.org>
---
 Said git-reliant project does use allow /optional/ use of libgit2
 via Perl Inline::C; but libgit2's git__date_parse() isn't part of
 the public API; and it's unlikely anybody using CentOS 7.x would
 run the latest libgit2 even if it were added today.

 t/t1500-rev-parse.sh | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

Show changes to t/t1500-rev-parse.sh +15 −0

diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index abdda360d5..deae916707 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -243,4 +243,19 @@ test_expect_success 'showing the superproject correctly' '
 	test_cmp expect out
 '
 
+# at least one external project depends on this behavior:
+test_expect_success 'rev-parse --since= unsqueezed ordering' '
+	x1=--since=1970-01-01T00:00:01Z &&
+	x2=--since=1970-01-01T00:00:02Z &&
+	x3=--since=1970-01-01T00:00:03Z &&
+	git rev-parse $x1 $x1 $x3 $x2 >actual &&
+	cat >expect <<-EOF &&
+	--max-age=1
+	--max-age=1
+	--max-age=3
+	--max-age=2
+	EOF
+	test_cmp expect actual
+'
+
 test_done

Jeff King· Feb 11, 2021, 11:18 UTC · re: Eric Wong · lore

Re: [PATCH] t1500: ensure current --since= behavior remains

On Wed, Feb 10, 2021 at 09:55:43PM +0000, Eric Wong wrote:

Show 8 quoted lines

> This behavior of git-rev-parse is observed since git 1.8.3.1
> at least(*), and likely earlier versions.
> 
> At least one git-reliant project in-the-wild relies on this
> current behavior of git-rev-parse being able to handle multiple
> --since= arguments without squeezing identical results together.
> So add a test to prevent the potential for regression in
> downstream projects.

I had to read this a few times to understand what "this behavior" meant. It is just: when given multiple --since options, output a --max-age for each of them, even though internally, Git's revision traversal will only use one (in the usual last-one-wins fashion).

I'm not sure if I was just being dense, or if this could be spelled out more clearly. :)

Out of curiosity, why does the other project want that? From your mention of libgit2's git__date_parse(), I assume it's something that wants to parse approxidates into timestamps in a script. Maybe we ought to provide a more direct and robust way of doing that. We have a similar need in t0006, but we use a test-helper program for it.

(I have no problem in the meantime with this patch, though; any new method for accomplishing this would want to give other projects time to adapt to its use).

-Peff

Eric Wong· Feb 11, 2021, 17:06 UTC · re: Jeff King · lore

Re: [PATCH] t1500: ensure current --since= behavior remains

Jeff King <peff@peff.net> wrote:

Show 18 quoted lines

> On Wed, Feb 10, 2021 at 09:55:43PM +0000, Eric Wong wrote:
> 
> > This behavior of git-rev-parse is observed since git 1.8.3.1
> > at least(*), and likely earlier versions.
> > 
> > At least one git-reliant project in-the-wild relies on this
> > current behavior of git-rev-parse being able to handle multiple
> > --since= arguments without squeezing identical results together.
> > So add a test to prevent the potential for regression in
> > downstream projects.
> 
> I had to read this a few times to understand what "this behavior" meant.
> It is just: when given multiple --since options, output a --max-age for
> each of them, even though internally, Git's revision traversal will only
> use one (in the usual last-one-wins fashion).
> 
> I'm not sure if I was just being dense, or if this could be spelled out
> more clearly. :)

*shrug* :> My brain struggles with coherent thought so I'm surprised anybody is able to understand me at all :x

Show 5 quoted lines

> Out of curiosity, why does the other project want that? From your
> mention of libgit2's git__date_parse(), I assume it's something that
> wants to parse approxidates into timestamps in a script. Maybe we ought
> to provide a more direct and robust way of doing that. We have a similar
> need in t0006, but we use a test-helper program for it.

It takes about 5ms for my system to run git-rev-parse once. I may be getting multiple approxidates at once, 1-2 in a typical input (start..end); but a strange or malicious input could have hundreds/thousands of approxidates to parse.

Thus, I'm batching up all the approxidates into one rev-parse invocation (up to system argv limits right now). With the output lines split into an array, walking the output/input arrays in parallel will match them up. Hypothetically, if rev-parse were to get clever and deduplicate or reject identical inputs; then the parallel walk would be broken.

> (I have no problem in the meantime with this patch, though; any new
> method for accomplishing this would want to give other projects time to
> adapt to its use).

Yes. I think I've mentioned some years/decade ago having general functionality along the lines of "git cat-file --batch" or fast-import would be nice (even for some existing scripts and tests shipped with git). (v)fork+execve is painful even on Linux.