Re: [PATCH v2 11/11] merge-ort: add implementation of type-changed rename handling

[Derrick Stolee <stolee@gmail.com>]

On 12/14/2020 11:21 AM, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@gmail.com>
> 
> Implement cases where renames are involved in type changes (i.e. the
> side of history that didn't rename the file changed its type from a
> regular file to a symlink or submodule).  There was some code to handle
> this in merge-recursive but only in the special case when the renamed
> file had no content changes.  The code here works differently -- it
> knows process_entry() can handle mode conflicts, so it does a few
> minimal tweaks to ensure process_entry() can just finish the job as
> needed.
> 
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  merge-ort.c | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/merge-ort.c b/merge-ort.c
> index 9aac33c8e31..11e33f56edf 100644
> --- a/merge-ort.c
> +++ b/merge-ort.c
> @@ -778,7 +778,32 @@ static int process_renames(struct merge_options *opt,
>  			 S_ISREG(newinfo->stages[target_index].mode));
>  		if (type_changed && collision) {
>  			/* special handling so later blocks can handle this */

Perhaps drop this comment, or incorporate it into the lower one?

> -			die("Not yet implemented");
> +			/*
> +			 * if type_changed && collision are both true, then this
> +			 * was really a double rename, but one side wasn't
> +			 * detected due to lack of break detection.  I.e.
> +			 * something like
> +			 *    orig: has normal file 'foo'
> +			 *    side1: renames 'foo' to 'bar', adds 'foo' symlink
> +			 *    side2: renames 'foo' to 'bar'
> +			 * In this case, the foo->bar rename on side1 won't be
> +			 * detected because the new symlink named 'foo' is
> +			 * there and we don't do break detection.  But we detect
> +			 * this here because we don't want to merge the content
> +			 * of the foo symlink with the foo->bar file, so we
> +			 * have some logic to handle this special case.  The
> +			 * easiest way to do that is make 'bar' on side1 not
> +			 * be considered a colliding file but the other part
> +			 * of a normal rename.  If the file is very different,
> +			 * well we're going to get content merge conflicts
> +			 * anyway so it doesn't hurt.  And if the colliding
> +			 * file also has a different type, that'll be handled
> +			 * by the content merge logic in process_entry() too.
> +			 *
> +			 * See also t6430, 'rename vs. rename/symlink'

I appreciate the callout to a test that exercises this behavior.

> +			 */
> +			collision = 0;
> +		}

Here, we regain that closing curly brace, fixing the compiler errors from
earlier.

>  		if (source_deleted) {
>  			if (target_index == 1) {
>  				rename_branch = opt->branch1;
> @@ -858,7 +883,11 @@ static int process_renames(struct merge_options *opt,
>  			newinfo->pathnames[0] = oldpath;
>  			if (type_changed) {
>  				/* rename vs. typechange */
> -				die("Not yet implemented");
> +				/* Mark the original as resolved by removal */
> +				memcpy(&oldinfo->stages[0].oid, &null_oid,
> +				       sizeof(oldinfo->stages[0].oid));
> +				oldinfo->stages[0].mode = 0;
> +				oldinfo->filemask &= 0x06;

This matches your explanation in the comment above. I wonder if 0x06
could be less magical, but we are really deep in the weeds here already.

Thanks,
-Stolee