Re: [PATCH v9 15/20] ref-filter: modify the 'lstrip=<N>' option to work with negative '<N>'

On Wed, Dec 28, 2016 at 2:41 AM, Junio C Hamano [off-list ref] wrote:

Karthik Nayak [off-list ref] writes:

quoted

Currently the 'lstrip=<N>' option only takes a positive value '<N>'
and strips '<N>' slash-separated path components from the left. Modify
the 'lstrip' option to also take a negative number '<N>' which would
only _leave_ behind 'N' slash-separated path components from the left.

"would only leave behind N components from the left" sounds as if
the result is A/B, when you are given A/B/C/D/E and asked to
lstrip:-2.  Given these two tests added by the patch ...

quoted

+test_atom head refname:lstrip=-1 master
+test_atom head refname:lstrip=-2 heads/master

... I somehow think that is not what you wanted to say.  Instead,
you strip from the left as many as necessary and leave -N
components that appear at the right-most end, no?

Yup, you're correct it should be 'leave -N components from the right-most
end'. Will change that.

quoted

--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt

@@ -98,7 +98,8 @@ refname::
      abbreviation mode. If `lstrip=<N>` is appended, strips `<N>`
      slash-separated path components from the front of the refname
      (e.g., `%(refname:lstrip=2)` turns `refs/tags/foo` into `foo`.
-     `<N>` must be a positive integer.
+     if `<N>` is a negative number, then only `<N>` path components
+     are left behind.

I think positive <N> is so obvious not to require an example but it
is good that you have one.  The negative <N> case needs illustration
more than the positive case.  Perhaps something like:

    (e.g. %(refname:lstrip=-1) strips components of refs/tags/frotz
    from the left to leave only one component, i.e. 'frotz').

Good point, but i'll be using N = -2 rather than -1 since N=-1 can
also be obtained
by using N=2 as shown in the existing documentation. With N=-2 we differentiate
the use cases of N= positive and negative numbers.

diff --git a/Documentation/git-for-each-ref.txt

b/Documentation/git-for-each-ref.txt
index 9123c6f..814d77a 100644

--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt

@@ -99,7 +99,8 @@ refname::
        slash-separated path components from the front of the refname
        (e.g., `%(refname:lstrip=2)` turns `refs/tags/foo` into `foo`.
        if `<N>` is a negative number, then only `<N>` path components
-       are left behind.
+       are left behind. (e.g., `%(refname:lstrip=-2)` turns
+       `refs/tags/foo` into `tags/foo`).

Would %(refname:lstrip=-4) attempt to strip components of
refs/tags/frotz from the left to leave only four components, and
because the original does not have that many components, it ends
with refs/tags/frotz?

It ends up with 'refs/tags/frotz' since there are not enough components.

I am debating myself if we need something like "When the ref does
not have enough components, the result becomes an empty string if
stripping with positive <N>, or it becomes the full refname if
stripping with negative <N>.  Neither is an error." is necessary
here.  Or is it too obvious?

I had the same self-debate, and dropped it for being too obvious.

On Wed, Dec 28, 2016 at 8:38 AM, Jacob Keller [off-list ref] wrote:

I do not think it hurts to have, and makes this obvious.

But as Jacob mentioned, it doesn't hurt to mention the obvious
sometimes. So i'll
add that in :)

-- 
Regards,
Karthik Nayak