Subject: Re: [PATCH v5 1/3] blame: test to describe use of blame --reverse --first-parent

From: Junio C Hamano <[email-masked]>
Date: Fri, 30 Oct 2015 15:30:38 -0700

Max Kirillov <[email-masked]> writes:

> Reverse blame can be used to locate removal of lines which does not
> change adjacent lines. Such edits do not appear in non-reverse blame,
> because the adjacent lines last changed commit is older history, before
> the edit.
>
> For a big and active project which uses topic branches, or analogous
> feature, for example pull-requests, the history can contain many
> concurrent branches, and even after an edit merged into the target
> branch, there are still many (sometimes several tens or even hundreds)
> topic branch which do not contain it:
>
>  a0--a1-----*a2-*a3-a4...-*a100
>  |\         /   /         /
>  | b0-B1..bN   /         /
>  |\           /         /
>  | c0..   ..cN         /
>  \                    /
>   z0..            ..zN
>
> Here, the '*'s mark the first parent in merge, and uppercase B1 - the
> commit where the line being blamed for was removed. Since commits cN-zN
> do not contain the B1, the still have the line removed in B1, and
> reverce blame can report that the last commit for the line was zN
> (meaning that it was removed in a100). In fact it really does return
> some very late commit, and this makes it unusable for finding the B1
> commit.
>
> The search could be done by blame --reverse --first-parent. For range
> a0..a100 it would return a1, and then only one additional blame along
> the a0..bN will return the desired commit b0. But combining --reverse
> and --first-parent was forbidden in 95a4fb0eac, because incorrectly
> specified range could produce unexpected and meaningless result.
>
> Add test which describes the expected behavior of
> `blame --reverse --first-parent` in the case described above.
>
> Signed-off-by: Max Kirillov <[email-masked]>
> ---

There were a few obvious typos I spotted but other than that a very
understandable description.  Will queue.

Thanks.

>  t/t8009-blame-vs-topicbranches.sh | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100755 t/t8009-blame-vs-topicbranches.sh
>
> diff --git a/t/t8009-blame-vs-topicbranches.sh b/t/t8009-blame-vs-topicbranches.sh
> new file mode 100755
> index 0000000..175ad37
> --- /dev/null
> +++ b/t/t8009-blame-vs-topicbranches.sh
> @@ -0,0 +1,36 @@
> +#!/bin/sh
> +
> +test_description='blaming trough history with topic branches'
> +. ./test-lib.sh
> +
> +# Creates the history shown below. '*'s mark the first parent in the merges.
> +# The only line of file.t is changed in commit B2
> +#
> +#        +---C1
> +#       /      \
> +# A0--A1--*A2--*A3
> +#   \     /
> +#    B1-B2
> +#
> +test_expect_success setup '
> +	test_commit A0 file.t line0 &&
> +	test_commit A1 &&
> +	git reset --hard A0 &&
> +	test_commit B1 &&
> +	test_commit B2 file.t line0changed &&
> +	git reset --hard A1 &&
> +	test_merge A2 B2 &&
> +	git reset --hard A1 &&
> +	test_commit C1 &&
> +	git reset --hard A2 &&
> +	test_merge A3 C1
> +	'
> +
> +test_expect_failure 'blame --reverse --first-parent finds A1' '
> +	git blame --porcelain --reverse --first-parent A0..A3 -- file.t >actual_full &&
> +	head -n 1 <actual_full | sed -e "s/ .*//" >actual &&
> +	git rev-parse A1 >expect &&
> +	test_cmp expect actual
> +	'
> +
> +test_done