Re: [PATCH 3/3] am: avoid directory rename detection when calling recursive merge machinery

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Elijah,

On Wed, 29 Aug 2018, Elijah Newren wrote:

> Let's say you have the following three trees, where Base is from one commit
> behind either master or branch:
> 
>    Base  : bar_v1, foo/{file1, file2, file3}
>    branch: bar_v2, foo/{file1, file2},       goo/file3
>    master: bar_v3, foo/{file1, file2, file3}
> 
> Using git-am (or am-based rebase) to apply the changes from branch onto
> master results in the following tree:
> 
>    Result: bar_merged, goo/{file1, file2, file3}
> 
> This is not what users want; they did not rename foo/ -> goo/, they only
> renamed one file within that directory.  The reason this happens is am
> constructs fake trees (via build_fake_ancestor()) of the following form:
> 
>    Base_bfa  : bar_v1, foo/file3
>    branch_bfa: bar_v2, goo/file3
> 
> Combining these two trees with master's tree:
> 
>    master: bar_v3, foo/{file1, file2, file3},
> 
> You can see that merge_recursive_generic() would see branch_bfa as renaming
> foo/ -> goo/, and master as just adding both foo/file1 and foo/file2.  As
> such, it ends up with goo/{file1, file2, file3}
> 
> The core problem is that am does not have access to the original trees; it
> can only construct trees using the blobs involved in the patch.  As such,
> it is not safe to perform directory rename detection within am -3.

I read through all three patches, and they look fine to me!

Ciao,
Dscho

> 
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  builtin/am.c                    | 1 +
>  t/t3401-rebase-and-am-rename.sh | 4 ++--
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/builtin/am.c b/builtin/am.c
> index 2fc2d1e82c..1494a9be84 100644
> --- a/builtin/am.c
> +++ b/builtin/am.c
> @@ -1596,6 +1596,7 @@ static int fall_back_threeway(const struct am_state *state, const char *index_pa
>  	o.branch1 = "HEAD";
>  	their_tree_name = xstrfmt("%.*s", linelen(state->msg), state->msg);
>  	o.branch2 = their_tree_name;
> +	o.detect_directory_renames = 0;
>  
>  	if (state->quiet)
>  		o.verbosity = 0;
> diff --git a/t/t3401-rebase-and-am-rename.sh b/t/t3401-rebase-and-am-rename.sh
> index a87df9e675..94bdfbd69c 100755
> --- a/t/t3401-rebase-and-am-rename.sh
> +++ b/t/t3401-rebase-and-am-rename.sh
> @@ -152,7 +152,7 @@ test_expect_success 'rebase --interactive: NO directory rename' '
>  	)
>  '
>  
> -test_expect_failure 'rebase (am): NO directory rename' '
> +test_expect_success 'rebase (am): NO directory rename' '
>  	test_when_finished "git -C no-dir-rename rebase --abort" &&
>  	(
>  		cd no-dir-rename &&
> @@ -190,7 +190,7 @@ test_expect_success 'rebase --merge: NO directory rename' '
>  	)
>  '
>  
> -test_expect_failure 'am: NO directory rename' '
> +test_expect_success 'am: NO directory rename' '
>  	test_when_finished "git -C no-dir-rename am --abort" &&
>  	(
>  		cd no-dir-rename &&
> -- 
> 2.18.0.12.g97a29da30a
> 
>