Max Kirillov 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
> ---
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 000..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 &&
> + git rev-parse A1 >expect &&
> + test_cmp expect actual
> + '
> +
> +test_done
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