Re: [PATCH v3 10/12] files-backend: make reflog iterator go through per-worktree reflog

[Michael Haggerty <mhagger@alum.mit.edu>]

Hi,

I put off reviewing this patch, thinking that it would appear in a
re-roll, then never came back to it. :-(

On 04/23/2017 06:44 AM, Duy Nguyen wrote:
> On Sat, Apr 22, 2017 at 10:05:02AM +0200, Michael Haggerty wrote:
>> I find this implementation confusing:
>>
>> * `if (iter->worktree_dir_iterator)` sounds like it should mean
>>   that we are iterating over worktree references but it really means
>>   that we are iterating over the common references in a repository
>>   that is a linked worktree.
>> * `files_reflog_iterator_advance()` is called recursively, but only
>>   for the first worktree reference.
>> * `iter->worktree_dir_iterator` is moved over to `iter->dir_iterator`
>>   when the common refs are exhausted.
>>
>> Do you find it more readable as follows?:
> 
> It's a bit better, but while we're at it, why not take full advantage
> of iterator abstraction?
> 
> This replacement patch (with some unrelated bits removed to reduce
> distraction) adds a new meta ref-iterator that combine a per-repo and
> a per-worktree iterators together. The new iterator walks through both
> sub-iterators and drop the per-worktree results from the per-repo
> iterator, which will be replaced with results from per-worktree
> iterator.
> 
> You probably see where I'm going with this. When the new "linked
> worktree ref store" comes, it will combine two per-worktree and
> per-repo ref stores together and this iterator will come handy.
> 
> At that point, files-backend can go back to being oblivious about
> $GIT_DIR vs $GIT_COMMON_DIR and files_reflog_iterator_begin() will be
> reverted back to the version before this patch.

Yes, that's even better.

> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index 4149943a6e..817b7b5d5e 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> @@ -3432,23 +3423,37 @@ static struct ref_iterator_vtable files_reflog_iterator_vtable = {
>  	files_reflog_iterator_abort
>  };
>  
> -static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
> +static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
> +						  const char *gitdir)
>  {
> -	struct files_ref_store *refs =
> -		files_downcast(ref_store, REF_STORE_READ,
> -			       "reflog_iterator_begin");
>  	struct files_reflog_iterator *iter = xcalloc(1, sizeof(*iter));
>  	struct ref_iterator *ref_iterator = &iter->base;
>  	struct strbuf sb = STRBUF_INIT;
>  
>  	base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable);
> -	files_reflog_path(refs, &sb, NULL);
> +	strbuf_addf(&sb, "%s/logs", gitdir);
>  	iter->dir_iterator = dir_iterator_begin(sb.buf);
>  	iter->ref_store = ref_store;
>  	strbuf_release(&sb);
> +
>  	return ref_iterator;
>  }

Makes sense.

> +static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
> +{
> +	struct files_ref_store *refs =
> +		files_downcast(ref_store, REF_STORE_READ,
> +			       "reflog_iterator_begin");
> +
> +	if (!strcmp(refs->gitdir, refs->gitcommondir)) {
> +		return reflog_iterator_begin(ref_store, refs->gitcommondir);
> +	} else {
> +		return worktree_ref_iterator_begin(
> +			reflog_iterator_begin(ref_store, refs->gitcommondir),
> +			reflog_iterator_begin(ref_store, refs->gitdir));
> +	}
> +}
> +

Yes.

>  static int ref_update_reject_duplicates(struct string_list *refnames,
>  					struct strbuf *err)
>  {
> diff --git a/refs/iterator.c b/refs/iterator.c
> index bce1f192f7..93243a00c4 100644
> --- a/refs/iterator.c
> +++ b/refs/iterator.c
> @@ -40,6 +40,14 @@ void base_ref_iterator_free(struct ref_iterator *iter)
>  	free(iter);
>  }
>  
> +static void ref_iterator_copy_result(struct ref_iterator *dst,
> +				     const struct ref_iterator *src)
> +{
> +	dst->refname = src->refname;
> +	dst->oid = src->oid;
> +	dst->flags = src->flags;
> +}
> +
>  struct empty_ref_iterator {
>  	struct ref_iterator base;
>  };
> @@ -382,3 +390,100 @@ int do_for_each_ref_iterator(struct ref_iterator *iter,
>  		return -1;
>  	return retval;
>  }
> +
> +struct worktree_ref_iterator {
> +	struct ref_iterator base;
> +	struct ref_iterator *per_repo_iterator;
> +	struct ref_iterator *per_worktree_iterator;
> +};
> +
> +static int worktree_ref_iterator_advance(struct ref_iterator *ref_iterator)
> +{
> +	struct worktree_ref_iterator *iter =
> +		(struct worktree_ref_iterator *)ref_iterator;
> +	int ok;
> +
> +	while (1) {
> +		struct ref_iterator **subiter;
> +		int normal_only;
> +
> +		if (iter->per_repo_iterator) {
> +			subiter = &iter->per_repo_iterator;
> +			/*
> +			 * If we are in a worktree, then we only
> +			 * include "normal" common references:
> +			 */
> +			normal_only = !!iter->per_worktree_iterator;
> +		} else if (iter->per_worktree_iterator) {
> +			subiter = &iter->per_worktree_iterator;
> +			normal_only = 0;
> +		} else {
> +			ok = ITER_DONE;
> +			break;
> +		}
> +
> +		ok = ref_iterator_advance(*subiter);
> +		if (ok == ITER_ERROR) {
> +			*subiter = NULL;
> +			break;
> +		} else if (ok == ITER_DONE) {
> +			*subiter = NULL;
> +			/* There might still be worktree refs left: */
> +			continue;
> +		}
> +
> +		if (normal_only &&
> +		    ref_type((*subiter)->refname) != REF_TYPE_NORMAL)
> +			continue;
> +
> +		ref_iterator_copy_result(&iter->base, *subiter);
> +		return ITER_OK;
> +	}
> +
> +	if (ref_iterator_abort(ref_iterator) == ITER_ERROR)
> +		return ITER_ERROR;
> +
> +	return ok;
> +}
> +
> +static int worktree_ref_iterator_peel(struct ref_iterator *ref_iterator,
> +					 struct object_id *peeled)
> +{
> +	die("BUG: ref_iterator_peel() called for reflog_iterator");
> +}
> +
> +static int worktree_ref_iterator_abort(struct ref_iterator *ref_iterator)
> +{
> +	struct worktree_ref_iterator *iter =
> +		(struct worktree_ref_iterator *)ref_iterator;
> +	int ok = ITER_DONE;
> +
> +	if (iter->per_repo_iterator)
> +		ok = ref_iterator_abort(iter->per_repo_iterator);
> +
> +	if (iter->per_worktree_iterator) {
> +		int ok2 = ref_iterator_abort(iter->per_worktree_iterator);
> +		if (ok2 == ITER_ERROR)
> +			ok = ok2;
> +	}
> +
> +	base_ref_iterator_free(ref_iterator);
> +	return ok;
> +}
> +
> +static struct ref_iterator_vtable worktree_ref_iterator_vtable = {
> +	worktree_ref_iterator_advance,
> +	worktree_ref_iterator_peel,
> +	worktree_ref_iterator_abort
> +};
> +
> +struct ref_iterator *worktree_ref_iterator_begin(struct ref_iterator *per_repo,
> +						 struct ref_iterator *per_worktree)
> +{
> +	struct worktree_ref_iterator *iter = xcalloc(1, sizeof(*iter));
> +
> +	base_ref_iterator_init(&iter->base, &worktree_ref_iterator_vtable);
> +	iter->per_repo_iterator = per_repo;
> +	iter->per_worktree_iterator = per_worktree;
> +	return &iter->base;
> +}
> diff --git a/refs/refs-internal.h b/refs/refs-internal.h
> index 690498698e..dcb1f1d73d 100644
> --- a/refs/refs-internal.h
> +++ b/refs/refs-internal.h
> @@ -387,6 +387,14 @@ struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
>  					       const char *prefix,
>  					       int trim);
>  
> +/*
> + * Wrap per_repo and per_worktree iterators. Traverse per_repo
> + * iterator, drop per-worktree refs. Then traverse per_worktree
> + * iterator.
> + */
> +struct ref_iterator *worktree_ref_iterator_begin(struct ref_iterator *per_repo,
> +						 struct ref_iterator *per_worktree);
> +
>  /* Internal implementation of reference iteration: */
>  
>  /*
> 
> 

I think `worktree_ref_iterator_begin()` could be implemented with a lot
less code via a `merge_ref_iterator`. You would need to define a
`ref_iterator_select_fn`, which could look like something like this:

enum iterator_selection worktree_iterator_select_fn(
		struct ref_iterator *iter0, struct ref_iterator *iter1,
		void *cb_data)
{
	if (iter0) {
		if (ref_type(iter0->refname) != REF_TYPE_NORMAL)
			return ITER_SKIP_0;
		return ITER_SELECT_0;
	} else if (iter1) {
		return ITER_SELECT_1;
	} else {
		return ITER_SELECT_DONE;
	}
}

Then `worktree_ref_iterator_begin()` is simply

struct ref_iterator *worktree_ref_iterator_begin(struct ref_iterator
*per_repo,
						 struct ref_iterator *per_worktree)
{
	return merge_ref_iterator_begin(per_repo, per_worktree,
					worktree_iterator_select_fn, NULL);
}

For references (as opposed to reflogs) you would want to interleave the
outputs from the two input iterators in the correct order. See
`overlay_iterator_select()` for how that can be done.

Michael