Re: [PATCH v2 07/13] merge-ort: populate caches of rename detection results

[Derrick Stolee <stolee@gmail.com>]

On 5/3/21 10:12 PM, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@gmail.com>
> 
> Fill in cache_pairs, cached_target_names, and cached_irrelevant based on
> rename detection results.  Future commits will make use of these values.

Thank you for continuing to break this down into nice-sized pieces.

> +static void possibly_cache_new_pair(struct rename_info *renames,
> +				    struct diff_filepair *p,
> +				    unsigned side,
> +				    char *new_path)
> +{
> +	char *old_value;
> +	int dir_renamed_side = 0;
> +
> +	if (new_path) {
> +		/*
> +		 * Directory renames happen on the other side of history from
> +		 * the side that adds new files to the old directory.
> +		 */
> +		dir_renamed_side = 3 - side;

Neat trick. Side is in { 1, 2 } so this makes sense.

> +	} else {
> +		int val = strintmap_get(&renames->relevant_sources[side],
> +					p->one->path);
> +		if (val == RELEVANT_NO_MORE) {
> +			assert(p->status == 'D');
> +			strset_add(&renames->cached_irrelevant[side],
> +				   p->one->path);

Ok, I see a transition here from a relevant side to an
irrelevant one.

> +		}
> +		if (val <= 0)
> +			return;
> +	}
> +
> +	if (p->status == 'D') {
> +		/*
> +		 * If we already had this delete, we'll just set it's value
> +		 * to NULL again, so no harm.
> +		 */
> +		strmap_put(&renames->cached_pairs[side], p->one->path, NULL);
> +	} else if (p->status == 'R') {
> +		if (new_path) {
> +			new_path = xstrdup(new_path);
> +			old_value = strmap_put(&renames->cached_pairs[dir_renamed_side],
> +					       p->two->path, new_path);
> +			strset_add(&renames->cached_target_names[dir_renamed_side],
> +				   new_path);
> +			assert(!old_value);

This assert implies that p->status == 'R' only if this is the
first side (and first commit) to show a rename, right?

> +		}
> +		if (!new_path)
> +			new_path = p->two->path;
> +		new_path = xstrdup(new_path);

If new_path was provided as non-NULL, then this is the second
time we are dup-ing it. However, that seems correct because we
want a different copy or every time we add it to the cached_pairs
and cached_target_names data.

> +		old_value = strmap_put(&renames->cached_pairs[side],
> +				       p->one->path, new_path);
> +		strset_add(&renames->cached_target_names[side],
> +			   new_path);

Since we appear to be doing this in multiple places, would this
be a good place for a helper method? We could have it take a
`const char *new_path` and have the helper manage the `xstrdup()`
so we never forget to do that exactly once per insert to these
sets.

> +		free(old_value);
> +	} else if (p->status == 'A' && new_path) {
> +		new_path = xstrdup(new_path);
> +		old_value = strmap_put(&renames->cached_pairs[dir_renamed_side],
> +				       p->two->path, new_path);
> +		strset_add(&renames->cached_target_names[dir_renamed_side],
> +			   new_path);
> +		assert(!old_value);

And here's the third instance, making the "three is many" rule
kick in. A helper method would help make this easier. You can
also have a parameter corresponding to whether you need to
free() the old_value or assert it is NULL.

> +	}
> +}
> +
>  static int compare_pairs(const void *a_, const void *b_)
>  {
>  	const struct diff_filepair *a = *((const struct diff_filepair **)a_);
> @@ -2415,6 +2474,7 @@ static int collect_renames(struct merge_options *opt,
>  		char *new_path; /* non-NULL only with directory renames */
>  
>  		if (p->status != 'A' && p->status != 'R') {
> +			possibly_cache_new_pair(renames, p, side_index, NULL);
>  			diff_free_filepair(p);
>  			continue;
>  		}
> @@ -2426,11 +2486,11 @@ static int collect_renames(struct merge_options *opt,
>  						      &collisions,
>  						      &clean);
>  
> +		possibly_cache_new_pair(renames, p, side_index, new_path);
>  		if (p->status != 'R' && !new_path) {
>  			diff_free_filepair(p);
>  			continue;
>  		}
> -

nit: this deletion seems unnecessary.

>  		if (new_path)
>  			apply_directory_rename_modifications(opt, p, new_path);
>  
> @@ -3701,8 +3761,16 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
>  					 NULL, 1);
>  		strmap_init_with_options(&renames->dir_renames[i],
>  					 NULL, 0);
> +		/*
> +		 * relevant_sources uses -1 for the default, because we need
> +		 * to be able to distinguish not-in-strintmap from valid
> +		 * relevant_source values from enum file_rename_relevance.
> +		 * In particular, possibly_cache_new_pair() expects a negative
> +		 * value for not-found entries.
> +		 */
>  		strintmap_init_with_options(&renames->relevant_sources[i],
> -					    0, NULL, 0);
> +					    -1 /* explicitly invalid */,
> +					    NULL, 0);
>  		strmap_init_with_options(&renames->cached_pairs[i],
>  					 NULL, 1);
>  		strset_init_with_options(&renames->cached_irrelevant[i],
> 

Functionally looks good. I just had some nits about organization.

Thanks,
-Stolee