Unexpected behavior with :/<text> references

Hello,

I'm experiencing strange behavior with :/<text> references, which seems to be inconsistent with the explanation in the docs on two counts. First, sometimes the matched commit is not the youngest. Second, some commits cannot be found at all, even if they are reachable from HEAD.

Here is a script to reproduce the behavior (Git built from current pu):

    #!/bin/sh
    export GIT_CONFIG_NOSYSTEM=1
    export GIT_ATTR_NOSYSTEM=1
    cd "$(mktemp -d --suffix .gitrepro)"

    git --version
    git init

    git commit -q --allow-empty -m initial
    git commit -q --allow-empty -m foo
    git checkout -q -b early-branch
    git commit -q --allow-empty -m foobar
    git checkout -q --detach
    git commit -q --allow-empty -m foobarbaz

    echo
    echo "The following should all print 'foobarbaz':"
    git show --format=%s ':/foo' --
    git show --format=%s ':/foobar' --
    git show --format=%s ':/foobarbaz' --

    echo
    echo "With an explicit branch:"
    git branch late-branch
    git show --format=%s ':/foo' --
    git show --format=%s ':/foobar' --
    git show --format=%s ':/foobarbaz' --

Here is the output on my machine:

    git version 2.18.0.516.g6fb7f6652
    Initialized empty Git repository in /tmp/tmp.WeCD0QZPIf.gitrepro/.git/

    The following should all print 'foobarbaz':
    foo
    foobar
    fatal: bad revision ':/foobarbaz'

    With an explicit branch:
    foo
    foobarbaz
    foobarbaz

First, the commit with message "foobar" clearly matches the regular expression /foo/ as well as /foobar/, but ":/foo" resolves to an older commit. However, Documentation/revisions.txt indicates that a :/<text> reference should resolve to the _youngest_ matching commit.

Second, the commit with message "foobarbaz" is reachable from HEAD, and yet the regular expression /foobarbaz/ fails to match it. The same documentation indicates that :/<text> references find commits reachable from any ref, and the glossary entry for "ref" states that HEAD is a "special-purpose ref" even though it does not begin with "refs/".

It looks to me like references reachable from `master` are always picked over other references, and that references reachable only from HEAD are not matched at all.

Is the observed behavior intentional? If so, what am I misunderstanding?

Thanks! WC

(for searchability: colon slash text references)

After further investigation, it appears that ":/foo" indeed resolves to the commit with message "foobar" (in the above example) if the commits are not all created at the same time: e.g., by adding `sleep 1` between the commit commands, or exporting `GIT_AUTHOR_DATE`.

This leaves only the question of why :/<text> references don't resolve to commits reachable only from HEAD, and whether this is the best behavior.

On Sun, Jul 08, 2018 at 10:13:12PM -0700, William Chargin wrote:

I suspect it's actually GIT_COMMITTER_DATE (but I didn't dig into it, so I could be wrong). "Youngest" in terms of commits generally refers to the committer date.

I agree that it would make sense to look at HEAD here. The point of ":/" is to search everything reachable, and HEAD is part of that reachability. _Usually_ it doesn't matter because HEAD is pointing to another ref, but the detached case is an exception.

Doing this would bring us in line with the behavior of other parts of Git. E.g., f0298cf1c6 (revision walker: include a detached HEAD in --all, 2009-01-16).

The patch is probably this:

Yep, I agree with your analysis. I'd be happy to test and commit this, probably later today.

Thanks for your input, and for the patch!

Best, WC