builtin/mv: refactor to use struct strvec

Memory allocation patterns in git-mv(1) are extremely hard to follow:
We copy around string pointers into manually-managed arrays, some of
which alias each other, but only sometimes, while we also drop some of
those strings at other times without ever daring to free them.

While this may be my own subjective feeling, it seems like others have
given up as the code has multiple calls to `UNLEAK()`. These are not
sufficient though, and git-mv(1) is still leaking all over the place
even with them.

Refactor the code to instead track strings in `struct strvec`. While
this has the effect of effectively duplicating some of the strings
without an actual need, it is way easier to reason about and fixes all
of the aliasing of memory that has been going on. It allows us to get
rid of the `UNLEAK()` calls and also fixes leaks that those calls did
not paper over.

Mark tests which are now leak-free accordingly.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/mv.c

@@ -20,6 +20,7 @@
 #include "read-cache-ll.h"
 #include "repository.h"
 #include "setup.h"
+#include "strvec.h"
 #include "submodule.h"
 #include "entry.h"
 
@@ -38,42 +39,32 @@ enum update_mode {
 #define DUP_BASENAME 1
 #define KEEP_TRAILING_SLASH 2
 
-static const char **internal_prefix_pathspec(const char *prefix,
-					     const char **pathspec,
-					     int count, unsigned flags)
+static void internal_prefix_pathspec(struct strvec *out,
+				     const char *prefix,
+				     const char **pathspec,
+				     int count, unsigned flags)
 {
-	int i;
-	const char **result;
 	int prefixlen = prefix ? strlen(prefix) : 0;
-	ALLOC_ARRAY(result, count + 1);
 
 	/* Create an intermediate copy of the pathspec based on the flags */
-	for (i = 0; i < count; i++) {
-		int length = strlen(pathspec[i]);
-		int to_copy = length;
-		char *it;
+	for (int i = 0; i < count; i++) {
+		size_t length = strlen(pathspec[i]);
+		size_t to_copy = length;
+		const char *maybe_basename;
+		char *trimmed, *prefixed_path;
+
 		while (!(flags & KEEP_TRAILING_SLASH) &&
 		       to_copy > 0 && is_dir_sep(pathspec[i][to_copy - 1]))
 			to_copy--;
 
-		it = xmemdupz(pathspec[i], to_copy);
-		if (flags & DUP_BASENAME) {
-			result[i] = xstrdup(basename(it));
-			free(it);
-		} else {
-			result[i] = it;
-		}
-	}
-	result[count] = NULL;
+		trimmed = xmemdupz(pathspec[i], to_copy);
+		maybe_basename = (flags & DUP_BASENAME) ? basename(trimmed) : trimmed;
+		prefixed_path = prefix_path(prefix, prefixlen, maybe_basename);
+		strvec_push(out, prefixed_path);
 
-	/* Prefix the pathspec and free the old intermediate strings */
-	for (i = 0; i < count; i++) {
-		const char *match = prefix_path(prefix, prefixlen, result[i]);
-		free((char *) result[i]);
-		result[i] = match;
+		free(prefixed_path);
+		free(trimmed);
 	}
-
-	return result;
 }
 
 static char *add_slash(const char *path)
@@ -176,7 +167,10 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 		OPT_BOOL(0, "sparse", &ignore_sparse, N_("allow updating entries outside of the sparse-checkout cone")),
 		OPT_END(),
 	};
-	const char **source, **destination, **dest_path, **submodule_gitfile;
+	struct strvec sources = STRVEC_INIT;
+	struct strvec dest_paths = STRVEC_INIT;
+	struct strvec destinations = STRVEC_INIT;
+	const char **submodule_gitfile;
 	char *dst_w_slash = NULL;
 	const char **src_dir = NULL;
 	int src_dir_nr = 0, src_dir_alloc = 0;
@@ -201,7 +195,7 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 	if (repo_read_index(the_repository) < 0)
 		die(_("index file corrupt"));
 
-	source = internal_prefix_pathspec(prefix, argv, argc, 0);
+	internal_prefix_pathspec(&sources, prefix, argv, argc, 0);
 	CALLOC_ARRAY(modes, argc);
 
 	/*
@@ -212,41 +206,39 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 	flags = KEEP_TRAILING_SLASH;
 	if (argc == 1 && is_directory(argv[0]) && !is_directory(argv[1]))
 		flags = 0;
-	dest_path = internal_prefix_pathspec(prefix, argv + argc, 1, flags);
-	dst_w_slash = add_slash(dest_path[0]);
+	internal_prefix_pathspec(&dest_paths, prefix, argv + argc, 1, flags);
+	dst_w_slash = add_slash(dest_paths.v[0]);
 	submodule_gitfile = xcalloc(argc, sizeof(char *));
 
-	if (dest_path[0][0] == '\0')
+	if (dest_paths.v[0][0] == '\0')
 		/* special case: "." was normalized to "" */
-		destination = internal_prefix_pathspec(dest_path[0], argv, argc, DUP_BASENAME);
-	else if (!lstat(dest_path[0], &st) &&
-			S_ISDIR(st.st_mode)) {
-		destination = internal_prefix_pathspec(dst_w_slash, argv, argc, DUP_BASENAME);
+		internal_prefix_pathspec(&destinations, dest_paths.v[0], argv, argc, DUP_BASENAME);
+	else if (!lstat(dest_paths.v[0], &st) && S_ISDIR(st.st_mode)) {
+		internal_prefix_pathspec(&destinations, dst_w_slash, argv, argc, DUP_BASENAME);
+	} else if (!path_in_sparse_checkout(dst_w_slash, the_repository->index) &&
+		   empty_dir_has_sparse_contents(dst_w_slash)) {
+		internal_prefix_pathspec(&destinations, dst_w_slash, argv, argc, DUP_BASENAME);
+		dst_mode = SKIP_WORKTREE_DIR;
+	} else if (argc != 1) {
+		die(_("destination '%s' is not a directory"), dest_paths.v[0]);
 	} else {
-		if (!path_in_sparse_checkout(dst_w_slash, the_repository->index) &&
-		    empty_dir_has_sparse_contents(dst_w_slash)) {
-			destination = internal_prefix_pathspec(dst_w_slash, argv, argc, DUP_BASENAME);
-			dst_mode = SKIP_WORKTREE_DIR;
-		} else if (argc != 1) {
-			die(_("destination '%s' is not a directory"), dest_path[0]);
-		} else {
-			destination = dest_path;
-			/*
-			 * <destination> is a file outside of sparse-checkout
-			 * cone. Insist on cone mode here for backward
-			 * compatibility. We don't want dst_mode to be assigned
-			 * for a file when the repo is using no-cone mode (which
-			 * is deprecated at this point) sparse-checkout. As
-			 * SPARSE here is only considering cone-mode situation.
-			 */
-			if (!path_in_cone_mode_sparse_checkout(destination[0], the_repository->index))
-				dst_mode = SPARSE;
-		}
+		strvec_pushv(&destinations, dest_paths.v);
+
+		/*
+		 * <destination> is a file outside of sparse-checkout
+		 * cone. Insist on cone mode here for backward
+		 * compatibility. We don't want dst_mode to be assigned
+		 * for a file when the repo is using no-cone mode (which
+		 * is deprecated at this point) sparse-checkout. As
+		 * SPARSE here is only considering cone-mode situation.
+		 */
+		if (!path_in_cone_mode_sparse_checkout(destinations.v[0], the_repository->index))
+			dst_mode = SPARSE;
 	}
 
 	/* Checking */
 	for (i = 0; i < argc; i++) {
-		const char *src = source[i], *dst = destination[i];
+		const char *src = sources.v[i], *dst = destinations.v[i];
 		int length;
 		const char *bad = NULL;
 		int skip_sparse = 0;
@@ -330,8 +322,6 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 			src_dir[src_dir_nr++] = src;
 
 			n = argc + last - first;
-			REALLOC_ARRAY(source, n);
-			REALLOC_ARRAY(destination, n);
 			REALLOC_ARRAY(modes, n);
 			REALLOC_ARRAY(submodule_gitfile, n);
 
@@ -341,12 +331,16 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 			for (j = 0; j < last - first; j++) {
 				const struct cache_entry *ce = the_repository->index->cache[first + j];
 				const char *path = ce->name;
-				source[argc + j] = path;
-				destination[argc + j] =
-					prefix_path(dst_with_slash, dst_with_slash_len, path + length + 1);
+				char *prefixed_path = prefix_path(dst_with_slash, dst_with_slash_len, path + length + 1);
+
+				strvec_push(&sources, path);
+				strvec_push(&destinations, prefixed_path);
+
 				memset(modes + argc + j, 0, sizeof(enum update_mode));
 				modes[argc + j] |= ce_skip_worktree(ce) ? SPARSE : INDEX;
 				submodule_gitfile[argc + j] = NULL;
+
+				free(prefixed_path);
 			}
 
 			free(dst_with_slash);
@@ -430,8 +424,8 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 remove_entry:
 		if (--argc > 0) {
 			int n = argc - i;
-			MOVE_ARRAY(source + i, source + i + 1, n);
-			MOVE_ARRAY(destination + i, destination + i + 1, n);
+			strvec_remove(&sources, i);
+			strvec_remove(&destinations, i);
 			MOVE_ARRAY(modes + i, modes + i + 1, n);
 			MOVE_ARRAY(submodule_gitfile + i,
 				   submodule_gitfile + i + 1, n);
@@ -448,7 +442,7 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 	}
 
 	for (i = 0; i < argc; i++) {
-		const char *src = source[i], *dst = destination[i];
+		const char *src = sources.v[i], *dst = destinations.v[i];
 		enum update_mode mode = modes[i];
 		int pos;
 		int sparse_and_dirty = 0;
@@ -576,8 +570,9 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 	string_list_clear(&src_for_dst, 0);
 	string_list_clear(&dirty_paths, 0);
 	string_list_clear(&only_match_skip_worktree, 0);
-	UNLEAK(source);
-	UNLEAK(dest_path);
+	strvec_clear(&sources);
+	strvec_clear(&dest_paths);
+	strvec_clear(&destinations);
 	free(submodule_gitfile);
 	free(modes);
 	return ret;

t/t4001-diff-rename.sh

@@ -3,9 +3,9 @@
 # Copyright (c) 2005 Junio C Hamano
 #
 
-test_description='Test rename detection in diff engine.
+test_description='Test rename detection in diff engine.'
 
-'
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-diff.sh
 

t/t4043-diff-rename-binary.sh

@@ -5,6 +5,7 @@
 
 test_description='Move a binary file'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 

t/t4120-apply-popt.sh

@@ -5,6 +5,7 @@
 
 test_description='git apply -p handling.'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success setup '

t/t6400-merge-df.sh

@@ -7,6 +7,7 @@ test_description='Test merge with directory/file conflicts'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'prepare repository' '

t/t6412-merge-large-rename.sh

@@ -4,6 +4,7 @@ test_description='merging with large rename matrix'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 count() {

t/t6426-merge-skip-unneeded-updates.sh

@@ -22,6 +22,7 @@ test_description="merge cases"
 #                     underscore notation is to differentiate different
 #                     files that might be renamed into each other's paths.)
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-merge.sh
 

t/t6429-merge-sequence-rename-caching.sh

@@ -2,6 +2,7 @@
 
 test_description="remember regular & dir renames in sequence of merges"
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 #