Re: [PATCH v2 02/11] merge-one-file: rewrite in C

> Alban Gruin <alban.gruin@gmail.com> writes:
> 
>> diff --git a/builtin/merge-one-file.c b/builtin/merge-one-file.c
>> new file mode 100644
>> index 0000000000..306a86c2f0
>> --- /dev/null
>> +++ b/builtin/merge-one-file.c
>> @@ -0,0 +1,85 @@
>> +/*
>> + * Builtin "git merge-one-file"
>> + *
>> + * Copyright (c) 2020 Alban Gruin
>> + *
>> + * Based on git-merge-one-file.sh, written by Linus Torvalds.
>> + *
>> + * This is the git per-file merge utility, called with
>> + *
>> + *   argv[1] - original file SHA1 (or empty)
>> + *   argv[2] - file in branch1 SHA1 (or empty)
>> + *   argv[3] - file in branch2 SHA1 (or empty)
>> + *   argv[4] - pathname in repository
>> + *   argv[5] - original file mode (or empty)
>> + *   argv[6] - file in branch1 mode (or empty)
>> + *   argv[7] - file in branch2 mode (or empty)
>> + *
>> + * Handle some trivial cases. The _really_ trivial cases have been
>> + * handled already by git read-tree, but that one doesn't do any merges
>> + * that might change the tree layout.
>> + */
>> +
>> +#include "cache.h"
>> +#include "builtin.h"
>> +#include "lockfile.h"
>> +#include "merge-strategies.h"
>> +
>> +static const char builtin_merge_one_file_usage[] =
>> +	"git merge-one-file <orig blob> <our blob> <their blob> <path> "
>> +	"<orig mode> <our mode> <their mode>\n\n"
>> +	"Blob ids and modes should be empty for missing files.";
>> +
>> +int cmd_merge_one_file(int argc, const char **argv, const char *prefix)
>> +{
>> +	struct object_id orig_blob, our_blob, their_blob,
>> +		*p_orig_blob = NULL, *p_our_blob = NULL, *p_their_blob = NULL;
>> +	unsigned int orig_mode = 0, our_mode = 0, their_mode = 0, ret = 0;
>> +	struct lock_file lock = LOCK_INIT;
>> +
>> +	if (argc != 8)
>> +		usage(builtin_merge_one_file_usage);
>> +
>> +	if (repo_read_index(the_repository) < 0)
>> +		die("invalid index");
>> +
>> +	repo_hold_locked_index(the_repository, &lock, LOCK_DIE_ON_ERROR);
> 
> I do understand why we would want merge_strategies_one_file() helper
> introduced by this step so that the helper can work in an arbitrary
> repository (hence taking a pointer to repository structure as one of
> its parameters).
> 
> But the "merge-one-file" command will always work in the_repository.
> I do not see a point in using helpers that can work in an arbitrary
> repository, like repo_read_index() or repo_hold_locked_index(), in
> the above.  I only see downsides --- it is longer to read, makes
> readers wonder if there is something tricky involving another
> repository going on, etc.
> 

>> +	if (!get_oid(argv[1], &orig_blob)) {
>> +		p_orig_blob = &orig_blob;
>> +		orig_mode = strtol(argv[5], NULL, 8);
> 
> Write a wrapper around strtol(...,...,8) to reduce repetition, and
> make sure you do not pass NULL as the second parameter to strtol()
> to always check you parsed the string to the end.
> 
>> +	ret = merge_strategies_one_file(the_repository,
>> +					p_orig_blob, p_our_blob, p_their_blob, argv[4],
>> +					orig_mode, our_mode, their_mode);
> 
> Here, as I said above, it is perfectly fine to pass
> the_repository().
> 
>> +	if (ret) {
>> +		rollback_lock_file(&lock);
>> +		return ret;
>> +	}
>> +
>> +	return write_locked_index(the_repository->index, &lock, COMMIT_LOCK);
> 
> Likewise, I do not see much point in saying the_repository->index; the_index
> is a perfectly fine short-hand.
> 
> -%<-
>> +static int do_merge_one_file(struct index_state *istate,
>> +			     const struct object_id *orig_blob,
>> +			     const struct object_id *our_blob,
>> +			     const struct object_id *their_blob, const char *path,
>> +			     unsigned int orig_mode, unsigned int our_mode, unsigned int their_mode)
>> +{
>> +	int ret, i, dest;
>> +	mmbuffer_t result = {NULL, 0};
>> +	mmfile_t mmfs[3];
>> +	struct ll_merge_options merge_opts = {0};
>> +	struct cache_entry *ce;
>> +
>> +	if (our_mode == S_IFLNK || their_mode == S_IFLNK)
>> +		return error(_("%s: Not merging symbolic link changes."), path);
>> +	else if (our_mode == S_IFGITLINK || their_mode == S_IFGITLINK)
>> +		return error(_("%s: Not merging conflicting submodule changes."), path);
>> +
>> +	read_mmblob(mmfs + 1, our_blob);
>> +	read_mmblob(mmfs + 2, their_blob);
>> +
>> +	if (orig_blob) {
>> +		printf(_("Auto-merging %s\n"), path);
>> +		read_mmblob(mmfs + 0, orig_blob);
>> +	} else {
>> +		printf(_("Added %s in both, but differently.\n"), path);
>> +		read_mmblob(mmfs + 0, &null_oid);
>> +	}
>> +
>> +	merge_opts.xdl_opts = XDL_MERGE_ZEALOUS_ALNUM;
>> +	ret = ll_merge(&result, path,
>> +		       mmfs + 0, "orig",
>> +		       mmfs + 1, "our",
>> +		       mmfs + 2, "their",
>> +		       istate, &merge_opts);
>> +
>> +	for (i = 0; i < 3; i++)
>> +		free(mmfs[i].ptr);
>> +
>> +	if (ret > 127 || !orig_blob)
>> +		ret = error(_("content conflict in %s"), path);
> 
> The original only checked if ret is zero or non-zero; here we
> require ret to be large.  Intended?  
> 
> ll_merge() that called ll_xdl_merge() (i.e. the most common case)
> would return the value returned from xdl_merge(), which can be -1
> when we got an error before calling xdl_do_merge().  xdl_do_merge()
> in turn can return -1.  The most common case returns the value
> returned from xdl_cleanup_merge(), which is 0 for clean merge, and
> any positive integer (not clipped to 127 or 128) for conflicted one.
> 

>> +	/* Create the working tree file, using "our tree" version from
>> +	   the index, and then store the result of the merge. */
> 
> Style. (cf. Documentation/CodingGuidelines).
> 
>> +	ce = index_file_exists(istate, path, strlen(path), 0);
>> +	if (!ce)
>> +		BUG("file is not present in the cache?");
>> +
>> +	unlink(path);
>> +	dest = open(path, O_WRONLY | O_CREAT, ce->ce_mode);
>> +	write_in_full(dest, result.ptr, result.size);
> 
> If open() fails, we write to a bogus file descriptor here.
> 
>> +	close(dest);
>> +
>> +	free(result.ptr);
>> +
>> +	if (ret && our_mode != their_mode)
>> +		return error(_("permission conflict: %o->%o,%o in %s"),
>> +			     orig_mode, our_mode, their_mode, path);
>> +	if (ret)
>> +		return 1;
> 
> What is the error returning convention around here?  Our usual
> convention is that 0 signals a success, and negative reports an
> error.  Returning the value returned from add_file_to_index() below,
> and error() above, are consistent with the convention, but this one
> returns 1 that is not.  When deviating from convention, it needs to
> be documented for the callers in a comment before the function
> definition.
> 

> 		/*
> 		 * The backend exits with 1 when conflicts are
> 		 * left to be resolved, with 2 when it does not
> 		 * handle the given merge at all.
> 		 */

>> +
>> +	return add_file_to_index(istate, path, 0);
>> +}
> 
> 
> 
>> +int merge_strategies_one_file(struct repository *r,
>> +			      const struct object_id *orig_blob,
>> +			      const struct object_id *our_blob,
>> +			      const struct object_id *their_blob, const char *path,
>> +			      unsigned int orig_mode, unsigned int our_mode,
>> +			      unsigned int their_mode)
>> +{
>> +	if (orig_blob &&
>> +	    ((!their_blob && our_blob && oideq(orig_blob, our_blob)) ||
>> +	     (!our_blob && their_blob && oideq(orig_blob, their_blob))))
>> +		/* Deleted in both or deleted in one and unchanged in
>> +		   the other */
>> +		return merge_one_file_deleted(r->index,
>> +					      orig_blob, our_blob, their_blob, path,
>> +					      orig_mode, our_mode, their_mode);
>> +	else if (!orig_blob && our_blob && !their_blob) {
>> +		/* Added in one.  The other side did not add and we
>> +		   added so there is nothing to be done, except making
>> +		   the path merged. */
>> +		return add_to_index_cacheinfo(r->index, our_mode, our_blob, path);
>> +	} else if (!orig_blob && !our_blob && their_blob) {
>> +		printf(_("Adding %s\n"), path);
>> +
>> +		if (file_exists(path))
>> +			return error(_("untracked %s is overwritten by the merge."), path);
>> +
>> +		if (add_to_index_cacheinfo(r->index, their_mode, their_blob, path))
>> +			return 1;
>> +		return checkout_from_index(r->index, path);
>> +	} else if (!orig_blob && our_blob && their_blob &&
>> +		   oideq(our_blob, their_blob)) {
>> +		/* Added in both, identically (check for same
>> +		   permissions). */
>> +		if (our_mode != their_mode)
>> +			return error(_("File %s added identically in both branches, "
>> +				       "but permissions conflict %o->%o."),
>> +				     path, our_mode, their_mode);
>> +
>> +		printf(_("Adding %s\n"), path);
>> +
>> +		if (add_to_index_cacheinfo(r->index, our_mode, our_blob, path))
>> +			return 1;
>> +		return checkout_from_index(r->index, path);
>> +	} else if (our_blob && their_blob)
>> +		/* Modified in both, but differently. */
>> +		return do_merge_one_file(r->index,
>> +					 orig_blob, our_blob, their_blob, path,
>> +					 orig_mode, our_mode, their_mode);
>> +	else {
>> +		char *orig_hex = "", *our_hex = "", *their_hex = "";
>> +
>> +		if (orig_blob)
>> +			orig_hex = oid_to_hex(orig_blob);
>> +		if (our_blob)
>> +			our_hex = oid_to_hex(our_blob);
>> +		if (their_blob)
>> +			their_hex = oid_to_hex(their_blob);
> 
> Prepare three char [] buffers and use oid_to_hex_r() instead,
> instead of relying that we'd have sufficient number of entries in
> the rotating buffer.
> 
>> +		return error(_("%s: Not handling case %s -> %s -> %s"),
>> +			     path, orig_hex, our_hex, their_hex);
>> +	}
>> +
>> +	return 0;
>> +}
>> diff --git a/merge-strategies.h b/merge-strategies.h
>> new file mode 100644
>> index 0000000000..b527d145c7
>> --- /dev/null
>> +++ b/merge-strategies.h
>> @@ -0,0 +1,13 @@
>> +#ifndef MERGE_STRATEGIES_H
>> +#define MERGE_STRATEGIES_H
>> +
>> +#include "object.h"
>> +
>> +int merge_strategies_one_file(struct repository *r,
>> +			      const struct object_id *orig_blob,
>> +			      const struct object_id *our_blob,
>> +			      const struct object_id *their_blob, const char *path,
>> +			      unsigned int orig_mode, unsigned int our_mode,
>> +			      unsigned int their_mode);
>> +
>> +#endif /* MERGE_STRATEGIES_H */
>> diff --git a/t/t6415-merge-dir-to-symlink.sh b/t/t6415-merge-dir-to-symlink.sh
>> index 2eddcc7664..5fb74e39a0 100755
>> --- a/t/t6415-merge-dir-to-symlink.sh
>> +++ b/t/t6415-merge-dir-to-symlink.sh
>> @@ -94,7 +94,7 @@ test_expect_success SYMLINKS 'a/b was resolved as symlink' '
>>  	test -h a/b
>>  '
>>  
>> -test_expect_failure 'do not lose untracked in merge (resolve)' '
>> +test_expect_success 'do not lose untracked in merge (resolve)' '
>>  	git reset --hard &&
>>  	git checkout baseline^0 &&
>>  	>a/b/c/e &&