thodg/libgit2/src/diff_tform.c

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• Hash : 4c462bb6
  Author :
  Date : 2021-04-13T13:20:34
  

  diff: Fix bug in git_diff_find_similar. When a split src gets turned into a rename, it should also lose the IS_RENAME_TARGET flag, so that it doesn't get processed in a subsequent iteration as a rename target. Doing so can cause an assertion failure because it no longer has the SPLIT flag. Fixes #5811.

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• src/diff_tform.c

• /*
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  
  #include "diff_tform.h"
  
  #include "git2/config.h"
  #include "git2/blob.h"
  #include "git2/sys/hashsig.h"
  
  #include "diff.h"
  #include "diff_generate.h"
  #include "path.h"
  #include "futils.h"
  #include "config.h"
  
  git_diff_delta *git_diff__delta_dup(
  	const git_diff_delta *d, git_pool *pool)
  {
  	git_diff_delta *delta = git__malloc(sizeof(git_diff_delta));
  	if (!delta)
  		return NULL;
  
  	memcpy(delta, d, sizeof(git_diff_delta));
  	GIT_DIFF_FLAG__CLEAR_INTERNAL(delta->flags);
  
  	if (d->old_file.path != NULL) {
  		delta->old_file.path = git_pool_strdup(pool, d->old_file.path);
  		if (delta->old_file.path == NULL)
  			goto fail;
  	}
  
  	if (d->new_file.path != d->old_file.path && d->new_file.path != NULL) {
  		delta->new_file.path = git_pool_strdup(pool, d->new_file.path);
  		if (delta->new_file.path == NULL)
  			goto fail;
  	} else {
  		delta->new_file.path = delta->old_file.path;
  	}
  
  	return delta;
  
  fail:
  	git__free(delta);
  	return NULL;
  }
  
  git_diff_delta *git_diff__merge_like_cgit(
  	const git_diff_delta *a,
  	const git_diff_delta *b,
  	git_pool *pool)
  {
  	git_diff_delta *dup;
  
  	/* Emulate C git for merging two diffs (a la 'git diff <sha>').
  	 *
  	 * When C git does a diff between the work dir and a tree, it actually
  	 * diffs with the index but uses the workdir contents.  This emulates
  	 * those choices so we can emulate the type of diff.
  	 *
  	 * We have three file descriptions here, let's call them:
  	 *  f1 = a->old_file
  	 *  f2 = a->new_file AND b->old_file
  	 *  f3 = b->new_file
  	 */
  
  	/* If one of the diffs is a conflict, just dup it */
  	if (b->status == GIT_DELTA_CONFLICTED)
  		return git_diff__delta_dup(b, pool);
  	if (a->status == GIT_DELTA_CONFLICTED)
  		return git_diff__delta_dup(a, pool);
  
  	/* if f2 == f3 or f2 is deleted, then just dup the 'a' diff */
  	if (b->status == GIT_DELTA_UNMODIFIED || a->status == GIT_DELTA_DELETED)
  		return git_diff__delta_dup(a, pool);
  
  	/* otherwise, base this diff on the 'b' diff */
  	if ((dup = git_diff__delta_dup(b, pool)) == NULL)
  		return NULL;
  
  	/* If 'a' status is uninteresting, then we're done */
  	if (a->status == GIT_DELTA_UNMODIFIED ||
  		a->status == GIT_DELTA_UNTRACKED ||
  		a->status == GIT_DELTA_UNREADABLE)
  		return dup;
  
  	GIT_ASSERT_WITH_RETVAL(b->status != GIT_DELTA_UNMODIFIED, NULL);
  
  	/* A cgit exception is that the diff of a file that is only in the
  	 * index (i.e. not in HEAD nor workdir) is given as empty.
  	 */
  	if (dup->status == GIT_DELTA_DELETED) {
  		if (a->status == GIT_DELTA_ADDED) {
  			dup->status = GIT_DELTA_UNMODIFIED;
  			dup->nfiles = 2;
  		}
  		/* else don't overwrite DELETE status */
  	} else {
  		dup->status = a->status;
  		dup->nfiles = a->nfiles;
  	}
  
  	git_oid_cpy(&dup->old_file.id, &a->old_file.id);
  	dup->old_file.mode  = a->old_file.mode;
  	dup->old_file.size  = a->old_file.size;
  	dup->old_file.flags = a->old_file.flags;
  
  	return dup;
  }
  
  int git_diff__merge(
  	git_diff *onto, const git_diff *from, git_diff__merge_cb cb)
  {
  	int error = 0;
  	git_pool onto_pool;
  	git_vector onto_new;
  	git_diff_delta *delta;
  	bool ignore_case, reversed;
  	unsigned int i, j;
  
  	GIT_ASSERT_ARG(onto);
  	GIT_ASSERT_ARG(from);
  
  	if (!from->deltas.length)
  		return 0;
  
  	ignore_case = ((onto->opts.flags & GIT_DIFF_IGNORE_CASE) != 0);
  	reversed    = ((onto->opts.flags & GIT_DIFF_REVERSE) != 0);
  
  	if (ignore_case != ((from->opts.flags & GIT_DIFF_IGNORE_CASE) != 0) ||
  		reversed    != ((from->opts.flags & GIT_DIFF_REVERSE) != 0)) {
  		git_error_set(GIT_ERROR_INVALID,
  			"attempt to merge diffs created with conflicting options");
  		return -1;
  	}
  
  	if (git_vector_init(&onto_new, onto->deltas.length, git_diff_delta__cmp) < 0 ||
  	    git_pool_init(&onto_pool, 1) < 0)
  		return -1;
  
  	for (i = 0, j = 0; i < onto->deltas.length || j < from->deltas.length; ) {
  		git_diff_delta *o = GIT_VECTOR_GET(&onto->deltas, i);
  		const git_diff_delta *f = GIT_VECTOR_GET(&from->deltas, j);
  		int cmp = !f ? -1 : !o ? 1 :
  			STRCMP_CASESELECT(ignore_case, o->old_file.path, f->old_file.path);
  
  		if (cmp < 0) {
  			delta = git_diff__delta_dup(o, &onto_pool);
  			i++;
  		} else if (cmp > 0) {
  			delta = git_diff__delta_dup(f, &onto_pool);
  			j++;
  		} else {
  			const git_diff_delta *left = reversed ? f : o;
  			const git_diff_delta *right = reversed ? o : f;
  
  			delta = cb(left, right, &onto_pool);
  			i++;
  			j++;
  		}
  
  		/* the ignore rules for the target may not match the source
  		 * or the result of a merged delta could be skippable...
  		 */
  		if (delta && git_diff_delta__should_skip(&onto->opts, delta)) {
  			git__free(delta);
  			continue;
  		}
  
  		if ((error = !delta ? -1 : git_vector_insert(&onto_new, delta)) < 0)
  			break;
  	}
  
  	if (!error) {
  		git_vector_swap(&onto->deltas, &onto_new);
  		git_pool_swap(&onto->pool, &onto_pool);
  
  		if ((onto->opts.flags & GIT_DIFF_REVERSE) != 0)
  			onto->old_src = from->old_src;
  		else
  			onto->new_src = from->new_src;
  
  		/* prefix strings also come from old pool, so recreate those.*/
  		onto->opts.old_prefix =
  			git_pool_strdup_safe(&onto->pool, onto->opts.old_prefix);
  		onto->opts.new_prefix =
  			git_pool_strdup_safe(&onto->pool, onto->opts.new_prefix);
  	}
  
  	git_vector_free_deep(&onto_new);
  	git_pool_clear(&onto_pool);
  
  	return error;
  }
  
  int git_diff_merge(git_diff *onto, const git_diff *from)
  {
  	return git_diff__merge(onto, from, git_diff__merge_like_cgit);
  }
  
  int git_diff_find_similar__hashsig_for_file(
  	void **out, const git_diff_file *f, const char *path, void *p)
  {
  	git_hashsig_option_t opt = (git_hashsig_option_t)(intptr_t)p;
  
  	GIT_UNUSED(f);
  	return git_hashsig_create_fromfile((git_hashsig **)out, path, opt);
  }
  
  int git_diff_find_similar__hashsig_for_buf(
  	void **out, const git_diff_file *f, const char *buf, size_t len, void *p)
  {
  	git_hashsig_option_t opt = (git_hashsig_option_t)(intptr_t)p;
  
  	GIT_UNUSED(f);
  	return git_hashsig_create((git_hashsig **)out, buf, len, opt);
  }
  
  void git_diff_find_similar__hashsig_free(void *sig, void *payload)
  {
  	GIT_UNUSED(payload);
  	git_hashsig_free(sig);
  }
  
  int git_diff_find_similar__calc_similarity(
  	int *score, void *siga, void *sigb, void *payload)
  {
  	int error;
  
  	GIT_UNUSED(payload);
  	error = git_hashsig_compare(siga, sigb);
  	if (error < 0)
  		return error;
  
  	*score = error;
  	return 0;
  }
  
  #define DEFAULT_THRESHOLD 50
  #define DEFAULT_BREAK_REWRITE_THRESHOLD 60
  #define DEFAULT_RENAME_LIMIT 200
  
  static int normalize_find_opts(
  	git_diff *diff,
  	git_diff_find_options *opts,
  	const git_diff_find_options *given)
  {
  	git_config *cfg = NULL;
  	git_hashsig_option_t hashsig_opts;
  
  	GIT_ERROR_CHECK_VERSION(given, GIT_DIFF_FIND_OPTIONS_VERSION, "git_diff_find_options");
  
  	if (diff->repo != NULL &&
  		git_repository_config__weakptr(&cfg, diff->repo) < 0)
  		return -1;
  
  	if (given)
  		memcpy(opts, given, sizeof(*opts));
  
  	if (!given ||
  		 (given->flags & GIT_DIFF_FIND_ALL) == GIT_DIFF_FIND_BY_CONFIG)
  	{
  		if (cfg) {
  			char *rule =
  				git_config__get_string_force(cfg, "diff.renames", "true");
  			int boolval;
  
  			if (!git__parse_bool(&boolval, rule) && !boolval)
  				/* don't set FIND_RENAMES if bool value is false */;
  			else if (!strcasecmp(rule, "copies") || !strcasecmp(rule, "copy"))
  				opts->flags |= GIT_DIFF_FIND_RENAMES | GIT_DIFF_FIND_COPIES;
  			else
  				opts->flags |= GIT_DIFF_FIND_RENAMES;
  
  			git__free(rule);
  		} else {
  			/* set default flag */
  			opts->flags |= GIT_DIFF_FIND_RENAMES;
  		}
  	}
  
  	/* some flags imply others */
  
  	if (opts->flags & GIT_DIFF_FIND_EXACT_MATCH_ONLY) {
  		/* if we are only looking for exact matches, then don't turn
  		 * MODIFIED items into ADD/DELETE pairs because it's too picky
  		 */
  		opts->flags &= ~(GIT_DIFF_FIND_REWRITES | GIT_DIFF_BREAK_REWRITES);
  
  		/* similarly, don't look for self-rewrites to split */
  		opts->flags &= ~GIT_DIFF_FIND_RENAMES_FROM_REWRITES;
  	}
  
  	if (opts->flags & GIT_DIFF_FIND_RENAMES_FROM_REWRITES)
  		opts->flags |= GIT_DIFF_FIND_RENAMES;
  
  	if (opts->flags & GIT_DIFF_FIND_COPIES_FROM_UNMODIFIED)
  		opts->flags |= GIT_DIFF_FIND_COPIES;
  
  	if (opts->flags & GIT_DIFF_BREAK_REWRITES)
  		opts->flags |= GIT_DIFF_FIND_REWRITES;
  
  #define USE_DEFAULT(X) ((X) == 0 || (X) > 100)
  
  	if (USE_DEFAULT(opts->rename_threshold))
  		opts->rename_threshold = DEFAULT_THRESHOLD;
  
  	if (USE_DEFAULT(opts->rename_from_rewrite_threshold))
  		opts->rename_from_rewrite_threshold = DEFAULT_THRESHOLD;
  
  	if (USE_DEFAULT(opts->copy_threshold))
  		opts->copy_threshold = DEFAULT_THRESHOLD;
  
  	if (USE_DEFAULT(opts->break_rewrite_threshold))
  		opts->break_rewrite_threshold = DEFAULT_BREAK_REWRITE_THRESHOLD;
  
  #undef USE_DEFAULT
  
  	if (!opts->rename_limit) {
  		if (cfg) {
  			opts->rename_limit = git_config__get_int_force(
  				cfg, "diff.renamelimit", DEFAULT_RENAME_LIMIT);
  		}
  
  		if (opts->rename_limit <= 0)
  			opts->rename_limit = DEFAULT_RENAME_LIMIT;
  	}
  
  	/* assign the internal metric with whitespace flag as payload */
  	if (!opts->metric) {
  		opts->metric = git__malloc(sizeof(git_diff_similarity_metric));
  		GIT_ERROR_CHECK_ALLOC(opts->metric);
  
  		opts->metric->file_signature = git_diff_find_similar__hashsig_for_file;
  		opts->metric->buffer_signature = git_diff_find_similar__hashsig_for_buf;
  		opts->metric->free_signature = git_diff_find_similar__hashsig_free;
  		opts->metric->similarity = git_diff_find_similar__calc_similarity;
  
  		if (opts->flags & GIT_DIFF_FIND_IGNORE_WHITESPACE)
  			hashsig_opts = GIT_HASHSIG_IGNORE_WHITESPACE;
  		else if (opts->flags & GIT_DIFF_FIND_DONT_IGNORE_WHITESPACE)
  			hashsig_opts = GIT_HASHSIG_NORMAL;
  		else
  			hashsig_opts = GIT_HASHSIG_SMART_WHITESPACE;
  		hashsig_opts |= GIT_HASHSIG_ALLOW_SMALL_FILES;
  		opts->metric->payload = (void *)hashsig_opts;
  	}
  
  	return 0;
  }
  
  static int insert_delete_side_of_split(
  	git_diff *diff, git_vector *onto, const git_diff_delta *delta)
  {
  	/* make new record for DELETED side of split */
  	git_diff_delta *deleted = git_diff__delta_dup(delta, &diff->pool);
  	GIT_ERROR_CHECK_ALLOC(deleted);
  
  	deleted->status = GIT_DELTA_DELETED;
  	deleted->nfiles = 1;
  	memset(&deleted->new_file, 0, sizeof(deleted->new_file));
  	deleted->new_file.path = deleted->old_file.path;
  	deleted->new_file.flags |= GIT_DIFF_FLAG_VALID_ID;
  
  	return git_vector_insert(onto, deleted);
  }
  
  static int apply_splits_and_deletes(
  	git_diff *diff, size_t expected_size, bool actually_split)
  {
  	git_vector onto = GIT_VECTOR_INIT;
  	size_t i;
  	git_diff_delta *delta;
  
  	if (git_vector_init(&onto, expected_size, git_diff_delta__cmp) < 0)
  		return -1;
  
  	/* build new delta list without TO_DELETE and splitting TO_SPLIT */
  	git_vector_foreach(&diff->deltas, i, delta) {
  		if ((delta->flags & GIT_DIFF_FLAG__TO_DELETE) != 0)
  			continue;
  
  		if ((delta->flags & GIT_DIFF_FLAG__TO_SPLIT) != 0 && actually_split) {
  			delta->similarity = 0;
  
  			if (insert_delete_side_of_split(diff, &onto, delta) < 0)
  				goto on_error;
  
  			if (diff->new_src == GIT_ITERATOR_WORKDIR)
  				delta->status = GIT_DELTA_UNTRACKED;
  			else
  				delta->status = GIT_DELTA_ADDED;
  			delta->nfiles = 1;
  			memset(&delta->old_file, 0, sizeof(delta->old_file));
  			delta->old_file.path = delta->new_file.path;
  			delta->old_file.flags |= GIT_DIFF_FLAG_VALID_ID;
  		}
  
  		/* clean up delta before inserting into new list */
  		GIT_DIFF_FLAG__CLEAR_INTERNAL(delta->flags);
  
  		if (delta->status != GIT_DELTA_COPIED &&
  			delta->status != GIT_DELTA_RENAMED &&
  			(delta->status != GIT_DELTA_MODIFIED || actually_split))
  			delta->similarity = 0;
  
  		/* insert into new list */
  		if (git_vector_insert(&onto, delta) < 0)
  			goto on_error;
  	}
  
  	/* cannot return an error past this point */
  
  	/* free deltas from old list that didn't make it to the new one */
  	git_vector_foreach(&diff->deltas, i, delta) {
  		if ((delta->flags & GIT_DIFF_FLAG__TO_DELETE) != 0)
  			git__free(delta);
  	}
  
  	/* swap new delta list into place */
  	git_vector_swap(&diff->deltas, &onto);
  	git_vector_free(&onto);
  	git_vector_sort(&diff->deltas);
  
  	return 0;
  
  on_error:
  	git_vector_free_deep(&onto);
  
  	return -1;
  }
  
  GIT_INLINE(git_diff_file *) similarity_get_file(git_diff *diff, size_t idx)
  {
  	git_diff_delta *delta = git_vector_get(&diff->deltas, idx / 2);
  	return (idx & 1) ? &delta->new_file : &delta->old_file;
  }
  
  typedef struct {
  	size_t idx;
  	git_iterator_t src;
  	git_repository *repo;
  	git_diff_file *file;
  	git_buf data;
  	git_odb_object *odb_obj;
  	git_blob *blob;
  } similarity_info;
  
  static int similarity_init(
  	similarity_info *info, git_diff *diff, size_t file_idx)
  {
  	info->idx  = file_idx;
  	info->src  = (file_idx & 1) ? diff->new_src : diff->old_src;
  	info->repo = diff->repo;
  	info->file = similarity_get_file(diff, file_idx);
  	info->odb_obj = NULL;
  	info->blob = NULL;
  	git_buf_init(&info->data, 0);
  
  	if (info->file->size > 0 || info->src == GIT_ITERATOR_WORKDIR)
  		return 0;
  
  	return git_diff_file__resolve_zero_size(
  		info->file, &info->odb_obj, info->repo);
  }
  
  static int similarity_sig(
  	similarity_info *info,
  	const git_diff_find_options *opts,
  	void **cache)
  {
  	int error = 0;
  	git_diff_file *file = info->file;
  
  	if (info->src == GIT_ITERATOR_WORKDIR) {
  		if ((error = git_repository_workdir_path(
  			&info->data, info->repo, file->path)) < 0)
  			return error;
  
  		/* if path is not a regular file, just skip this item */
  		if (!git_path_isfile(info->data.ptr))
  			return 0;
  
  		/* TODO: apply wd-to-odb filters to file data if necessary */
  
  		error = opts->metric->file_signature(
  			&cache[info->idx], info->file,
  			info->data.ptr, opts->metric->payload);
  	} else {
  		/* if we didn't initially know the size, we might have an odb_obj
  		 * around from earlier, so convert that, otherwise load the blob now
  		 */
  		if (info->odb_obj != NULL)
  			error = git_object__from_odb_object(
  				(git_object **)&info->blob, info->repo,
  				info->odb_obj, GIT_OBJECT_BLOB);
  		else
  			error = git_blob_lookup(&info->blob, info->repo, &file->id);
  
  		if (error < 0) {
  			/* if lookup fails, just skip this item in similarity calc */
  			git_error_clear();
  		} else {
  			size_t sz;
  
  			/* index size may not be actual blob size if filtered */
  			if (file->size != git_blob_rawsize(info->blob))
  				file->size = git_blob_rawsize(info->blob);
  
  			sz = git__is_sizet(file->size) ? (size_t)file->size : (size_t)-1;
  
  			error = opts->metric->buffer_signature(
  				&cache[info->idx], info->file,
  				git_blob_rawcontent(info->blob), sz, opts->metric->payload);
  		}
  	}
  
  	return error;
  }
  
  static void similarity_unload(similarity_info *info)
  {
  	if (info->odb_obj)
  		git_odb_object_free(info->odb_obj);
  
  	if (info->blob)
  		git_blob_free(info->blob);
  	else
  		git_buf_dispose(&info->data);
  }
  
  #define FLAG_SET(opts,flag_name) (((opts)->flags & flag_name) != 0)
  
  /* - score < 0 means files cannot be compared
   * - score >= 100 means files are exact match
   * - score == 0 means files are completely different
   */
  static int similarity_measure(
  	int *score,
  	git_diff *diff,
  	const git_diff_find_options *opts,
  	void **cache,
  	size_t a_idx,
  	size_t b_idx)
  {
  	git_diff_file *a_file = similarity_get_file(diff, a_idx);
  	git_diff_file *b_file = similarity_get_file(diff, b_idx);
  	bool exact_match = FLAG_SET(opts, GIT_DIFF_FIND_EXACT_MATCH_ONLY);
  	int error = 0;
  	similarity_info a_info, b_info;
  
  	*score = -1;
  
  	/* don't try to compare things that aren't files */
  	if (!GIT_MODE_ISBLOB(a_file->mode) || !GIT_MODE_ISBLOB(b_file->mode))
  		return 0;
  
  	/* if exact match is requested, force calculation of missing OIDs now */
  	if (exact_match) {
  		if (git_oid_is_zero(&a_file->id) &&
  			diff->old_src == GIT_ITERATOR_WORKDIR &&
  			!git_diff__oid_for_file(&a_file->id,
  				diff, a_file->path, a_file->mode, a_file->size))
  			a_file->flags |= GIT_DIFF_FLAG_VALID_ID;
  
  		if (git_oid_is_zero(&b_file->id) &&
  			diff->new_src == GIT_ITERATOR_WORKDIR &&
  			!git_diff__oid_for_file(&b_file->id,
  				diff, b_file->path, b_file->mode, b_file->size))
  			b_file->flags |= GIT_DIFF_FLAG_VALID_ID;
  	}
  
  	/* check OID match as a quick test */
  	if (git_oid__cmp(&a_file->id, &b_file->id) == 0) {
  		*score = 100;
  		return 0;
  	}
  
  	/* don't calculate signatures if we are doing exact match */
  	if (exact_match) {
  		*score = 0;
  		return 0;
  	}
  
  	memset(&a_info, 0, sizeof(a_info));
  	memset(&b_info, 0, sizeof(b_info));
  
  	/* set up similarity data (will try to update missing file sizes) */
  	if (!cache[a_idx] && (error = similarity_init(&a_info, diff, a_idx)) < 0)
  		return error;
  	if (!cache[b_idx] && (error = similarity_init(&b_info, diff, b_idx)) < 0)
  		goto cleanup;
  
  	/* check if file sizes are nowhere near each other */
  	if (a_file->size > 127 &&
  		b_file->size > 127 &&
  		(a_file->size > (b_file->size << 3) ||
  		 b_file->size > (a_file->size << 3)))
  		goto cleanup;
  
  	/* update signature cache if needed */
  	if (!cache[a_idx]) {
  		if ((error = similarity_sig(&a_info, opts, cache)) < 0)
  			goto cleanup;
  	}
  	if (!cache[b_idx]) {
  		if ((error = similarity_sig(&b_info, opts, cache)) < 0)
  			goto cleanup;
  	}
  
  	/* calculate similarity provided that the metric choose to process
  	 * both the a and b files (some may not if file is too big, etc).
  	 */
  	if (cache[a_idx] && cache[b_idx])
  		error = opts->metric->similarity(
  			score, cache[a_idx], cache[b_idx], opts->metric->payload);
  
  cleanup:
  	similarity_unload(&a_info);
  	similarity_unload(&b_info);
  
  	return error;
  }
  
  static int calc_self_similarity(
  	git_diff *diff,
  	const git_diff_find_options *opts,
  	size_t delta_idx,
  	void **cache)
  {
  	int error, similarity = -1;
  	git_diff_delta *delta = GIT_VECTOR_GET(&diff->deltas, delta_idx);
  
  	if ((delta->flags & GIT_DIFF_FLAG__HAS_SELF_SIMILARITY) != 0)
  		return 0;
  
  	error = similarity_measure(
  		&similarity, diff, opts, cache, 2 * delta_idx, 2 * delta_idx + 1);
  	if (error < 0)
  		return error;
  
  	if (similarity >= 0) {
  		delta->similarity = (uint16_t)similarity;
  		delta->flags |= GIT_DIFF_FLAG__HAS_SELF_SIMILARITY;
  	}
  
  	return 0;
  }
  
  static bool is_rename_target(
  	git_diff *diff,
  	const git_diff_find_options *opts,
  	size_t delta_idx,
  	void **cache)
  {
  	git_diff_delta *delta = GIT_VECTOR_GET(&diff->deltas, delta_idx);
  
  	/* skip things that aren't plain blobs */
  	if (!GIT_MODE_ISBLOB(delta->new_file.mode))
  		return false;
  
  	/* only consider ADDED, RENAMED, COPIED, and split MODIFIED as
  	 * targets; maybe include UNTRACKED if requested.
  	 */
  	switch (delta->status) {
  	case GIT_DELTA_UNMODIFIED:
  	case GIT_DELTA_DELETED:
  	case GIT_DELTA_IGNORED:
  	case GIT_DELTA_CONFLICTED:
  		return false;
  
  	case GIT_DELTA_MODIFIED:
  		if (!FLAG_SET(opts, GIT_DIFF_FIND_REWRITES) &&
  			!FLAG_SET(opts, GIT_DIFF_FIND_RENAMES_FROM_REWRITES))
  			return false;
  
  		if (calc_self_similarity(diff, opts, delta_idx, cache) < 0)
  			return false;
  
  		if (FLAG_SET(opts, GIT_DIFF_BREAK_REWRITES) &&
  			delta->similarity < opts->break_rewrite_threshold) {
  			delta->flags |= GIT_DIFF_FLAG__TO_SPLIT;
  			break;
  		}
  		if (FLAG_SET(opts, GIT_DIFF_FIND_RENAMES_FROM_REWRITES) &&
  			delta->similarity < opts->rename_from_rewrite_threshold) {
  			delta->flags |= GIT_DIFF_FLAG__TO_SPLIT;
  			break;
  		}
  
  		return false;
  
  	case GIT_DELTA_UNTRACKED:
  		if (!FLAG_SET(opts, GIT_DIFF_FIND_FOR_UNTRACKED))
  			return false;
  		break;
  
  	default: /* all other status values should be checked */
  		break;
  	}
  
  	delta->flags |= GIT_DIFF_FLAG__IS_RENAME_TARGET;
  	return true;
  }
  
  static bool is_rename_source(
  	git_diff *diff,
  	const git_diff_find_options *opts,
  	size_t delta_idx,
  	void **cache)
  {
  	git_diff_delta *delta = GIT_VECTOR_GET(&diff->deltas, delta_idx);
  
  	/* skip things that aren't blobs */
  	if (!GIT_MODE_ISBLOB(delta->old_file.mode))
  		return false;
  
  	switch (delta->status) {
  	case GIT_DELTA_ADDED:
  	case GIT_DELTA_UNTRACKED:
  	case GIT_DELTA_UNREADABLE:
  	case GIT_DELTA_IGNORED:
  	case GIT_DELTA_CONFLICTED:
  		return false;
  
  	case GIT_DELTA_DELETED:
  	case GIT_DELTA_TYPECHANGE:
  		break;
  
  	case GIT_DELTA_UNMODIFIED:
  		if (!FLAG_SET(opts, GIT_DIFF_FIND_COPIES_FROM_UNMODIFIED))
  			return false;
  		if (FLAG_SET(opts, GIT_DIFF_FIND_REMOVE_UNMODIFIED))
  			delta->flags |= GIT_DIFF_FLAG__TO_DELETE;
  		break;
  
  	default: /* MODIFIED, RENAMED, COPIED */
  		/* if we're finding copies, this could be a source */
  		if (FLAG_SET(opts, GIT_DIFF_FIND_COPIES))
  			break;
  
  		/* otherwise, this is only a source if we can split it */
  		if (!FLAG_SET(opts, GIT_DIFF_FIND_REWRITES) &&
  			!FLAG_SET(opts, GIT_DIFF_FIND_RENAMES_FROM_REWRITES))
  			return false;
  
  		if (calc_self_similarity(diff, opts, delta_idx, cache) < 0)
  			return false;
  
  		if (FLAG_SET(opts, GIT_DIFF_BREAK_REWRITES) &&
  			delta->similarity < opts->break_rewrite_threshold) {
  			delta->flags |= GIT_DIFF_FLAG__TO_SPLIT;
  			break;
  		}
  
  		if (FLAG_SET(opts, GIT_DIFF_FIND_RENAMES_FROM_REWRITES) &&
  			delta->similarity < opts->rename_from_rewrite_threshold)
  			break;
  
  		return false;
  	}
  
  	delta->flags |= GIT_DIFF_FLAG__IS_RENAME_SOURCE;
  	return true;
  }
  
  GIT_INLINE(bool) delta_is_split(git_diff_delta *delta)
  {
  	return (delta->status == GIT_DELTA_TYPECHANGE ||
  			(delta->flags & GIT_DIFF_FLAG__TO_SPLIT) != 0);
  }
  
  GIT_INLINE(bool) delta_is_new_only(git_diff_delta *delta)
  {
  	return (delta->status == GIT_DELTA_ADDED ||
  			delta->status == GIT_DELTA_UNTRACKED ||
  			delta->status == GIT_DELTA_UNREADABLE ||
  			delta->status == GIT_DELTA_IGNORED);
  }
  
  GIT_INLINE(void) delta_make_rename(
  	git_diff_delta *to, const git_diff_delta *from, uint16_t similarity)
  {
  	to->status     = GIT_DELTA_RENAMED;
  	to->similarity = similarity;
  	to->nfiles     = 2;
  	memcpy(&to->old_file, &from->old_file, sizeof(to->old_file));
  	to->flags &= ~GIT_DIFF_FLAG__TO_SPLIT;
  }
  
  typedef struct {
  	size_t   idx;
  	uint16_t similarity;
  } diff_find_match;
  
  int git_diff_find_similar(
  	git_diff *diff,
  	const git_diff_find_options *given_opts)
  {
  	size_t s, t;
  	int error = 0, result;
  	uint16_t similarity;
  	git_diff_delta *src, *tgt;
  	git_diff_find_options opts = GIT_DIFF_FIND_OPTIONS_INIT;
  	size_t num_deltas, num_srcs = 0, num_tgts = 0;
  	size_t tried_srcs = 0, tried_tgts = 0;
  	size_t num_rewrites = 0, num_updates = 0, num_bumped = 0;
  	size_t sigcache_size;
  	void **sigcache = NULL; /* cache of similarity metric file signatures */
  	diff_find_match *tgt2src = NULL;
  	diff_find_match *src2tgt = NULL;
  	diff_find_match *tgt2src_copy = NULL;
  	diff_find_match *best_match;
  	git_diff_file swap;
  
  	GIT_ASSERT_ARG(diff);
  
  	if ((error = normalize_find_opts(diff, &opts, given_opts)) < 0)
  		return error;
  
  	num_deltas = diff->deltas.length;
  
  	/* TODO: maybe abort if deltas.length > rename_limit ??? */
  	if (!num_deltas || !git__is_uint32(num_deltas))
  		goto cleanup;
  
  	/* No flags set; nothing to do */
  	if ((opts.flags & GIT_DIFF_FIND_ALL) == 0)
  		goto cleanup;
  
  	GIT_ERROR_CHECK_ALLOC_MULTIPLY(&sigcache_size, num_deltas, 2);
  	sigcache = git__calloc(sigcache_size, sizeof(void *));
  	GIT_ERROR_CHECK_ALLOC(sigcache);
  
  	/* Label rename sources and targets
  	 *
  	 * This will also set self-similarity scores for MODIFIED files and
  	 * mark them for splitting if break-rewrites is enabled
  	 */
  	git_vector_foreach(&diff->deltas, t, tgt) {
  		if (is_rename_source(diff, &opts, t, sigcache))
  			++num_srcs;
  
  		if (is_rename_target(diff, &opts, t, sigcache))
  			++num_tgts;
  
  		if ((tgt->flags & GIT_DIFF_FLAG__TO_SPLIT) != 0)
  			num_rewrites++;
  	}
  
  	/* if there are no candidate srcs or tgts, we're done */
  	if (!num_srcs || !num_tgts)
  		goto cleanup;
  
  	src2tgt = git__calloc(num_deltas, sizeof(diff_find_match));
  	GIT_ERROR_CHECK_ALLOC(src2tgt);
  	tgt2src = git__calloc(num_deltas, sizeof(diff_find_match));
  	GIT_ERROR_CHECK_ALLOC(tgt2src);
  
  	if (FLAG_SET(&opts, GIT_DIFF_FIND_COPIES)) {
  		tgt2src_copy = git__calloc(num_deltas, sizeof(diff_find_match));
  		GIT_ERROR_CHECK_ALLOC(tgt2src_copy);
  	}
  
  	/*
  	 * Find best-fit matches for rename / copy candidates
  	 */
  
  find_best_matches:
  	tried_tgts = num_bumped = 0;
  
  	git_vector_foreach(&diff->deltas, t, tgt) {
  		/* skip things that are not rename targets */
  		if ((tgt->flags & GIT_DIFF_FLAG__IS_RENAME_TARGET) == 0)
  			continue;
  
  		tried_srcs = 0;
  
  		git_vector_foreach(&diff->deltas, s, src) {
  			/* skip things that are not rename sources */
  			if ((src->flags & GIT_DIFF_FLAG__IS_RENAME_SOURCE) == 0)
  				continue;
  
  			/* calculate similarity for this pair and find best match */
  			if (s == t)
  				result = -1; /* don't measure self-similarity here */
  			else if ((error = similarity_measure(
  				&result, diff, &opts, sigcache, 2 * s, 2 * t + 1)) < 0)
  				goto cleanup;
  
  			if (result < 0)
  				continue;
  			similarity = (uint16_t)result;
  
  			/* is this a better rename? */
  			if (tgt2src[t].similarity < similarity &&
  				src2tgt[s].similarity < similarity)
  			{
  				/* eject old mapping */
  				if (src2tgt[s].similarity > 0) {
  					tgt2src[src2tgt[s].idx].similarity = 0;
  					num_bumped++;
  				}
  				if (tgt2src[t].similarity > 0) {
  					src2tgt[tgt2src[t].idx].similarity = 0;
  					num_bumped++;
  				}
  
  				/* write new mapping */
  				tgt2src[t].idx = s;
  				tgt2src[t].similarity = similarity;
  				src2tgt[s].idx = t;
  				src2tgt[s].similarity = similarity;
  			}
  
  			/* keep best absolute match for copies */
  			if (tgt2src_copy != NULL &&
  				tgt2src_copy[t].similarity < similarity)
  			{
  				tgt2src_copy[t].idx = s;
  				tgt2src_copy[t].similarity = similarity;
  			}
  
  			if (++tried_srcs >= num_srcs)
  				break;
  
  			/* cap on maximum targets we'll examine (per "tgt" file) */
  			if (tried_srcs > opts.rename_limit)
  				break;
  		}
  
  		if (++tried_tgts >= num_tgts)
  			break;
  	}
  
  	if (num_bumped > 0) /* try again if we bumped some items */
  		goto find_best_matches;
  
  	/*
  	 * Rewrite the diffs with renames / copies
  	 */
  
  	git_vector_foreach(&diff->deltas, t, tgt) {
  		/* skip things that are not rename targets */
  		if ((tgt->flags & GIT_DIFF_FLAG__IS_RENAME_TARGET) == 0)
  			continue;
  
  		/* check if this delta was the target of a similarity */
  		if (tgt2src[t].similarity)
  			best_match = &tgt2src[t];
  		else if (tgt2src_copy && tgt2src_copy[t].similarity)
  			best_match = &tgt2src_copy[t];
  		else
  			continue;
  
  		s = best_match->idx;
  		src = GIT_VECTOR_GET(&diff->deltas, s);
  
  		/* possible scenarios:
  		 * 1. from DELETE to ADD/UNTRACK/IGNORE = RENAME
  		 * 2. from DELETE to SPLIT/TYPECHANGE = RENAME + DELETE
  		 * 3. from SPLIT/TYPECHANGE to ADD/UNTRACK/IGNORE = ADD + RENAME
  		 * 4. from SPLIT/TYPECHANGE to SPLIT/TYPECHANGE = RENAME + SPLIT
  		 * 5. from OTHER to ADD/UNTRACK/IGNORE = OTHER + COPY
  		 */
  
  		if (src->status == GIT_DELTA_DELETED) {
  
  			if (delta_is_new_only(tgt)) {
  
  				if (best_match->similarity < opts.rename_threshold)
  					continue;
  
  				delta_make_rename(tgt, src, best_match->similarity);
  
  				src->flags |= GIT_DIFF_FLAG__TO_DELETE;
  				num_rewrites++;
  			} else {
  				GIT_ASSERT(delta_is_split(tgt));
  
  				if (best_match->similarity < opts.rename_from_rewrite_threshold)
  					continue;
  
  				memcpy(&swap, &tgt->old_file, sizeof(swap));
  
  				delta_make_rename(tgt, src, best_match->similarity);
  				num_rewrites--;
  
  				GIT_ASSERT(src->status == GIT_DELTA_DELETED);
  				memcpy(&src->old_file, &swap, sizeof(src->old_file));
  				memset(&src->new_file, 0, sizeof(src->new_file));
  				src->new_file.path = src->old_file.path;
  				src->new_file.flags |= GIT_DIFF_FLAG_VALID_ID;
  
  				num_updates++;
  
  				if (src2tgt[t].similarity > 0 && src2tgt[t].idx > t) {
  					/* what used to be at src t is now at src s */
  					tgt2src[src2tgt[t].idx].idx = s;
  				}
  			}
  		}
  
  		else if (delta_is_split(src)) {
  
  			if (delta_is_new_only(tgt)) {
  
  				if (best_match->similarity < opts.rename_threshold)
  					continue;
  
  				delta_make_rename(tgt, src, best_match->similarity);
  
  				src->status = (diff->new_src == GIT_ITERATOR_WORKDIR) ?
  					GIT_DELTA_UNTRACKED : GIT_DELTA_ADDED;
  				src->nfiles = 1;
  				memset(&src->old_file, 0, sizeof(src->old_file));
  				src->old_file.path = src->new_file.path;
  				src->old_file.flags |= GIT_DIFF_FLAG_VALID_ID;
  
  				src->flags &= ~GIT_DIFF_FLAG__TO_SPLIT;
  				num_rewrites--;
  
  				num_updates++;
  			} else {
  				GIT_ASSERT(delta_is_split(src));
  
  				if (best_match->similarity < opts.rename_from_rewrite_threshold)
  					continue;
  
  				memcpy(&swap, &tgt->old_file, sizeof(swap));
  
  				delta_make_rename(tgt, src, best_match->similarity);
  				num_rewrites--;
  				num_updates++;
  
  				memcpy(&src->old_file, &swap, sizeof(src->old_file));
  
  				/* if we've just swapped the new element into the correct
  				 * place, clear the SPLIT and RENAME_TARGET flags
  				 */
  				if (tgt2src[s].idx == t &&
  					tgt2src[s].similarity >
  					opts.rename_from_rewrite_threshold) {
  					src->status     = GIT_DELTA_RENAMED;
  					src->similarity = tgt2src[s].similarity;
  					tgt2src[s].similarity = 0;
  					src->flags &= ~(GIT_DIFF_FLAG__TO_SPLIT | GIT_DIFF_FLAG__IS_RENAME_TARGET);
  					num_rewrites--;
  				}
  				/* otherwise, if we just overwrote a source, update mapping */
  				else if (src2tgt[t].similarity > 0 && src2tgt[t].idx > t) {
  					/* what used to be at src t is now at src s */
  					tgt2src[src2tgt[t].idx].idx = s;
  				}
  
  				num_updates++;
  			}
  		}
  
  		else if (FLAG_SET(&opts, GIT_DIFF_FIND_COPIES)) {
  			if (tgt2src_copy[t].similarity < opts.copy_threshold)
  				continue;
  
  			/* always use best possible source for copy */
  			best_match = &tgt2src_copy[t];
  			src = GIT_VECTOR_GET(&diff->deltas, best_match->idx);
  
  			if (delta_is_split(tgt)) {
  				error = insert_delete_side_of_split(diff, &diff->deltas, tgt);
  				if (error < 0)
  					goto cleanup;
  				num_rewrites--;
  			}
  
  			if (!delta_is_split(tgt) && !delta_is_new_only(tgt))
  				continue;
  
  			tgt->status     = GIT_DELTA_COPIED;
  			tgt->similarity = best_match->similarity;
  			tgt->nfiles     = 2;
  			memcpy(&tgt->old_file, &src->old_file, sizeof(tgt->old_file));
  			tgt->flags &= ~GIT_DIFF_FLAG__TO_SPLIT;
  
  			num_updates++;
  		}
  	}
  
  	/*
  	 * Actually split and delete entries as needed
  	 */
  
  	if (num_rewrites > 0 || num_updates > 0)
  		error = apply_splits_and_deletes(
  			diff, diff->deltas.length - num_rewrites,
  			FLAG_SET(&opts, GIT_DIFF_BREAK_REWRITES) &&
  			!FLAG_SET(&opts, GIT_DIFF_BREAK_REWRITES_FOR_RENAMES_ONLY));
  
  cleanup:
  	git__free(tgt2src);
  	git__free(src2tgt);
  	git__free(tgt2src_copy);
  
  	if (sigcache) {
  		for (t = 0; t < num_deltas * 2; ++t) {
  			if (sigcache[t] != NULL)
  				opts.metric->free_signature(sigcache[t], opts.metric->payload);
  		}
  		git__free(sigcache);
  	}
  
  	if (!given_opts || !given_opts->metric)
  		git__free(opts.metric);
  
  	return error;
  }
  
  #undef FLAG_SET
  

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