Re: [PATCH v2 09/11] merge-ort: add implementation of rename/delete conflicts

[Derrick Stolee <stolee@gmail.com>]

On 12/14/2020 11:21 AM, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@gmail.com>
> 
> Implement rename/delete conflicts, i.e. one side renames a file and the
> other deletes the file.  This code replaces the following from
> merge-recurisve.c:
> 
>   * the code relevant to RENAME_DELETE in process_renames()
>   * the RENAME_DELETE case of process_entry()
>   * handle_rename_delete()
> 
> Also, there is some shared code from merge-recursive.c for multiple
> different rename cases which we will no longer need for this case (or
> other rename cases):
> 
>   * handle_change_delete()
>   * setup_rename_conflict_info()
> 
> The consolidation of five separate codepaths into one is made possible
> by a change in design: process_renames() tweaks the conflict_info
> entries within opt->priv->paths such that process_entry() can then
> handle all the non-rename conflict types (directory/file, modify/delete,
> etc.) orthogonally.  This means we're much less likely to miss special
> implementation of some kind of combination of conflict types (see
> commits brought in by 66c62eaec6 ("Merge branch 'en/merge-tests'",
> 2020-11-18), especially commit ef52778708 ("merge tests: expect improved
> directory/file conflict handling in ort", 2020-10-26) for more details).
> That, together with letting worktree/index updating be handled
> orthogonally in the merge_switch_to_result() function, dramatically
> simplifies the code for various special rename cases.
> 
> To be fair, there is a _slight_ tweak to process_entry() here, because
> rename/delete cases will also trigger the modify/delete codepath.
> However, we only want a modify/delete message to be printed for a
> rename/delete conflict if there is a content change in the renamed file
> in addition to the rename.  So process_renames() and process_entry()
> aren't quite fully orthogonal, but they are pretty close.

Thanks for adding this warning about the change to process_entry().

> @@ -657,6 +657,7 @@ static int process_renames(struct merge_options *opt,
>  		unsigned int old_sidemask;
>  		int target_index, other_source_index;
>  		int source_deleted, collision, type_changed;
> +		const char *rename_branch = NULL, *delete_branch = NULL;

Ah, here they are!

> +		if (source_deleted) {
> +			if (target_index == 1) {
> +				rename_branch = opt->branch1;
> +				delete_branch = opt->branch2;
> +			} else {
> +				rename_branch = opt->branch2;
> +				delete_branch = opt->branch1;
> +			}
>  		}
>  
>  		assert(source_deleted || oldinfo->filemask & old_sidemask);
> @@ -838,13 +847,26 @@ static int process_renames(struct merge_options *opt,
>  				   "to %s in %s, but deleted in %s."),
>  				 oldpath, newpath, rename_branch, delete_branch);

This context line is the previous use of rename_branch and delete_branch.
Perhaps the declarations, initialization, and first-use here are worth
their own patch?

>  		} else {
> +			/*
> +			 * a few different cases...start by copying the
> +			 * existing stage(s) from oldinfo over the newinfo
> +			 * and update the pathname(s).
> +			 */
> +			memcpy(&newinfo->stages[0], &oldinfo->stages[0],
> +			       sizeof(newinfo->stages[0]));
> +			newinfo->filemask |= (1 << MERGE_BASE);
> +			newinfo->pathnames[0] = oldpath;
>  			if (type_changed) {
>  				/* rename vs. typechange */
>  				die("Not yet implemented");
>  			} else if (source_deleted) {
>  				/* rename/delete */
> +				newinfo->path_conflict = 1;
> +				path_msg(opt, newpath, 0,
> +					 _("CONFLICT (rename/delete): %s renamed"
> +					   " to %s in %s, but deleted in %s."),
> +					 oldpath, newpath,
> +					 rename_branch, delete_branch);

Since the primary purpose of rename_branch and delete_branch appears to
be for these error messages, then likely the previous error message about
a rename/delete should just be promoted into this patch instead of the
previous.

In fact, the error messages are the exact same, but with slightly different
lines due to wrapping:

			path_msg(opt, newpath, 0,
				 _("CONFLICT (rename/delete): %s renamed "
				   "to %s in %s, but deleted in %s."),
				 oldpath, newpath, rename_branch, delete_branch);

and

				path_msg(opt, newpath, 0,
					 _("CONFLICT (rename/delete): %s renamed"
					   " to %s in %s, but deleted in %s."),
					 oldpath, newpath,
					 rename_branch, delete_branch);

I wonder if there is a way to group these together? Perhaps the nested
if/else if/else blocks could store a "conflict state" value that says
which CONFLICT message to print after the complicated branching is done.

Alternatively, this message appears to be written in the following case:

	source_deleted && !type_changed

your if/else if/else block could be rearranged as follows:

	if (collision && !source_deleted)
		/* collision: rename/add or rename/rename(2to1) */
	else if (!type_change && source_deleted)
		/* rename/delete or rename/add/delete or rename/rename(2to1)/delete */
	else if (!collision)
		/* a few different cases */

Of course, the thing I am missing is that copy of oldinfo->stages[0] into
newinfo->stages[0] along with changes to the filemask and pathnames! That
is likely why you need the two different markers, because the cases truly
are different in that subtle way.

>  				/* normal rename */
>  				die("Not yet implemented");
> @@ -1380,12 +1402,21 @@ static void process_entry(struct merge_options *opt,
>  		modify_branch = (side == 1) ? opt->branch1 : opt->branch2;
>  		delete_branch = (side == 1) ? opt->branch2 : opt->branch1;
>  
> -		path_msg(opt, path, 0,
> -			 _("CONFLICT (modify/delete): %s deleted in %s "
> -			   "and modified in %s.  Version %s of %s left "
> -			   "in tree."),
> -			 path, delete_branch, modify_branch,
> -			 modify_branch, path);
> +		if (ci->path_conflict &&
> +		    oideq(&ci->stages[0].oid, &ci->stages[side].oid)) {
> +			/*
> +			 * This came from a rename/delete; no action to take,
> +			 * but avoid printing "modify/delete" conflict notice
> +			 * since the contents were not modified.
> +			 */
> +		} else {
> +			path_msg(opt, path, 0,
> +				 _("CONFLICT (modify/delete): %s deleted in %s "
> +				   "and modified in %s.  Version %s of %s left "
> +				   "in tree."),
> +				 path, delete_branch, modify_branch,
> +				 modify_branch, path);
> +		}

Thanks,
-Stolee