Merge branch 'rs/unpack-trees-plug-leak'

* rs/unpack-trees-plug-leak:
  unpack-trees: free cache_entry array members for merges
  diff-lib, read-tree, unpack-trees: mark cache_entry array paramters const
  diff-lib, read-tree, unpack-trees: mark cache_entry pointers const
  unpack-trees: create working copy of merge entry in merged_entry
  unpack-trees: factor out dup_entry
  read-cache: mark cache_entry pointers const
  cache: mark cache_entry pointers const

6 files changed, 133 insertions, 88 deletions

diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 042ac1b84f..0f5d7fe23f 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -66,7 +66,7 @@ static int exclude_per_directory_cb(const struct option *opt, const char *arg,
 	return 0;
 }
 
-static void debug_stage(const char *label, struct cache_entry *ce,
+static void debug_stage(const char *label, const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	printf("%s ", label);
@@ -80,7 +80,8 @@ static void debug_stage(const char *label, struct cache_entry *ce,
 		       sha1_to_hex(ce->sha1));
 }
 
-static int debug_merge(struct cache_entry **stages, struct unpack_trees_options *o)
+static int debug_merge(const struct cache_entry * const *stages,
+		       struct unpack_trees_options *o)
 {
 	int i;
 
diff --git a/cache.h b/cache.h
index df532f8e4a..820aa05c7a 100644
--- a/cache.h
+++ b/cache.h
@@ -190,7 +190,8 @@ struct cache_entry {
  * another. But we never change the name, or the hash state!
  */
 #define CE_STATE_MASK (CE_HASHED | CE_UNHASHED)
-static inline void copy_cache_entry(struct cache_entry *dst, struct cache_entry *src)
+static inline void copy_cache_entry(struct cache_entry *dst,
+				    const struct cache_entry *src)
 {
 	unsigned int state = dst->ce_flags & CE_STATE_MASK;
 
@@ -222,7 +223,8 @@ static inline unsigned int create_ce_mode(unsigned int mode)
 		return S_IFGITLINK;
 	return S_IFREG | ce_permissions(mode);
 }
-static inline unsigned int ce_mode_from_stat(struct cache_entry *ce, unsigned int mode)
+static inline unsigned int ce_mode_from_stat(const struct cache_entry *ce,
+					     unsigned int mode)
 {
 	extern int trust_executable_bit, has_symlinks;
 	if (!has_symlinks && S_ISREG(mode) &&
@@ -480,8 +482,8 @@ extern void *read_blob_data_from_index(struct index_state *, const char *, unsig
 #define CE_MATCH_RACY_IS_DIRTY		02
 /* do stat comparison even if CE_SKIP_WORKTREE is true */
 #define CE_MATCH_IGNORE_SKIP_WORKTREE	04
-extern int ie_match_stat(const struct index_state *, struct cache_entry *, struct stat *, unsigned int);
-extern int ie_modified(const struct index_state *, struct cache_entry *, struct stat *, unsigned int);
+extern int ie_match_stat(const struct index_state *, const struct cache_entry *, struct stat *, unsigned int);
+extern int ie_modified(const struct index_state *, const struct cache_entry *, struct stat *, unsigned int);
 
 #define PATHSPEC_ONESTAR 1	/* the pathspec pattern sastisfies GFNM_ONESTAR */
 
diff --git a/diff-lib.c b/diff-lib.c
index f35de0ffa0..b6f4b21637 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -64,8 +64,9 @@ static int check_removed(const struct cache_entry *ce, struct stat *st)
  * commits, untracked content and/or modified content).
  */
 static int match_stat_with_submodule(struct diff_options *diffopt,
-				      struct cache_entry *ce, struct stat *st,
-				      unsigned ce_option, unsigned *dirty_submodule)
+				     const struct cache_entry *ce,
+				     struct stat *st, unsigned ce_option,
+				     unsigned *dirty_submodule)
 {
 	int changed = ce_match_stat(ce, st, ce_option);
 	if (S_ISGITLINK(ce->ce_mode)) {
@@ -237,7 +238,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 /* A file entry went away or appeared */
 static void diff_index_show_file(struct rev_info *revs,
 				 const char *prefix,
-				 struct cache_entry *ce,
+				 const struct cache_entry *ce,
 				 const unsigned char *sha1, int sha1_valid,
 				 unsigned int mode,
 				 unsigned dirty_submodule)
@@ -246,7 +247,7 @@ static void diff_index_show_file(struct rev_info *revs,
 		       sha1, sha1_valid, ce->name, dirty_submodule);
 }
 
-static int get_stat_data(struct cache_entry *ce,
+static int get_stat_data(const struct cache_entry *ce,
 			 const unsigned char **sha1p,
 			 unsigned int *modep,
 			 int cached, int match_missing,
@@ -283,7 +284,7 @@ static int get_stat_data(struct cache_entry *ce,
 }
 
 static void show_new_file(struct rev_info *revs,
-			  struct cache_entry *new,
+			  const struct cache_entry *new,
 			  int cached, int match_missing)
 {
 	const unsigned char *sha1;
@@ -302,8 +303,8 @@ static void show_new_file(struct rev_info *revs,
 }
 
 static int show_modified(struct rev_info *revs,
-			 struct cache_entry *old,
-			 struct cache_entry *new,
+			 const struct cache_entry *old,
+			 const struct cache_entry *new,
 			 int report_missing,
 			 int cached, int match_missing)
 {
@@ -362,8 +363,8 @@ static int show_modified(struct rev_info *revs,
  * give you the position and number of entries in the index).
  */
 static void do_oneway_diff(struct unpack_trees_options *o,
-	struct cache_entry *idx,
-	struct cache_entry *tree)
+			   const struct cache_entry *idx,
+			   const struct cache_entry *tree)
 {
 	struct rev_info *revs = o->unpack_data;
 	int match_missing, cached;
@@ -423,10 +424,11 @@ static void do_oneway_diff(struct unpack_trees_options *o,
  * the fairly complex unpack_trees() semantic requirements, including
  * the skipping, the path matching, the type conflict cases etc.
  */
-static int oneway_diff(struct cache_entry **src, struct unpack_trees_options *o)
+static int oneway_diff(const struct cache_entry * const *src,
+		       struct unpack_trees_options *o)
 {
-	struct cache_entry *idx = src[0];
-	struct cache_entry *tree = src[1];
+	const struct cache_entry *idx = src[0];
+	const struct cache_entry *tree = src[1];
 	struct rev_info *revs = o->unpack_data;
 
 	/*
diff --git a/read-cache.c b/read-cache.c
index 04ed561bfe..e6e046687e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -91,7 +91,7 @@ void fill_stat_cache_info(struct cache_entry *ce, struct stat *st)
 		ce_mark_uptodate(ce);
 }
 
-static int ce_compare_data(struct cache_entry *ce, struct stat *st)
+static int ce_compare_data(const struct cache_entry *ce, struct stat *st)
 {
 	int match = -1;
 	int fd = open(ce->name, O_RDONLY);
@@ -105,7 +105,7 @@ static int ce_compare_data(struct cache_entry *ce, struct stat *st)
 	return match;
 }
 
-static int ce_compare_link(struct cache_entry *ce, size_t expected_size)
+static int ce_compare_link(const struct cache_entry *ce, size_t expected_size)
 {
 	int match = -1;
 	void *buffer;
@@ -126,7 +126,7 @@ static int ce_compare_link(struct cache_entry *ce, size_t expected_size)
 	return match;
 }
 
-static int ce_compare_gitlink(struct cache_entry *ce)
+static int ce_compare_gitlink(const struct cache_entry *ce)
 {
 	unsigned char sha1[20];
 
@@ -143,7 +143,7 @@ static int ce_compare_gitlink(struct cache_entry *ce)
 	return hashcmp(sha1, ce->sha1);
 }
 
-static int ce_modified_check_fs(struct cache_entry *ce, struct stat *st)
+static int ce_modified_check_fs(const struct cache_entry *ce, struct stat *st)
 {
 	switch (st->st_mode & S_IFMT) {
 	case S_IFREG:
@@ -163,7 +163,7 @@ static int ce_modified_check_fs(struct cache_entry *ce, struct stat *st)
 	return 0;
 }
 
-static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
+static int ce_match_stat_basic(const struct cache_entry *ce, struct stat *st)
 {
 	unsigned int changed = 0;
 
@@ -239,7 +239,8 @@ static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
 	return changed;
 }
 
-static int is_racy_timestamp(const struct index_state *istate, struct cache_entry *ce)
+static int is_racy_timestamp(const struct index_state *istate,
+			     const struct cache_entry *ce)
 {
 	return (!S_ISGITLINK(ce->ce_mode) &&
 		istate->timestamp.sec &&
@@ -255,7 +256,7 @@ static int is_racy_timestamp(const struct index_state *istate, struct cache_entr
 }
 
 int ie_match_stat(const struct index_state *istate,
-		  struct cache_entry *ce, struct stat *st,
+		  const struct cache_entry *ce, struct stat *st,
 		  unsigned int options)
 {
 	unsigned int changed;
@@ -311,7 +312,8 @@ int ie_match_stat(const struct index_state *istate,
 }
 
 int ie_modified(const struct index_state *istate,
-		struct cache_entry *ce, struct stat *st, unsigned int options)
+		const struct cache_entry *ce,
+		struct stat *st, unsigned int options)
 {
 	int changed, changed_fs;
 
diff --git a/unpack-trees.c b/unpack-trees.c
index ede4299b83..57b40743a1 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -116,14 +116,20 @@ static void do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static void add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
-	unsigned int set, unsigned int clear)
+static struct cache_entry *dup_entry(const struct cache_entry *ce)
 {
 	unsigned int size = ce_size(ce);
 	struct cache_entry *new = xmalloc(size);
 
 	memcpy(new, ce, size);
-	do_add_entry(o, new, set, clear);
+	return new;
+}
+
+static void add_entry(struct unpack_trees_options *o,
+		      const struct cache_entry *ce,
+		      unsigned int set, unsigned int clear)
+{
+	do_add_entry(o, dup_entry(ce), set, clear);
 }
 
 /*
@@ -235,8 +241,11 @@ static int check_updates(struct unpack_trees_options *o)
 	return errs != 0;
 }
 
-static int verify_uptodate_sparse(struct cache_entry *ce, struct unpack_trees_options *o);
-static int verify_absent_sparse(struct cache_entry *ce, enum unpack_trees_error_types, struct unpack_trees_options *o);
+static int verify_uptodate_sparse(const struct cache_entry *ce,
+				  struct unpack_trees_options *o);
+static int verify_absent_sparse(const struct cache_entry *ce,
+				enum unpack_trees_error_types,
+				struct unpack_trees_options *o);
 
 static int apply_sparse_checkout(struct cache_entry *ce, struct unpack_trees_options *o)
 {
@@ -291,7 +300,8 @@ static int apply_sparse_checkout(struct cache_entry *ce, struct unpack_trees_opt
 	return 0;
 }
 
-static inline int call_unpack_fn(struct cache_entry **src, struct unpack_trees_options *o)
+static inline int call_unpack_fn(const struct cache_entry * const *src,
+				 struct unpack_trees_options *o)
 {
 	int ret = o->fn(src, o);
 	if (ret > 0)
@@ -320,7 +330,7 @@ static void mark_all_ce_unused(struct index_state *index)
 		index->cache[i]->ce_flags &= ~(CE_UNPACKED | CE_ADDED | CE_NEW_SKIP_WORKTREE);
 }
 
-static int locate_in_src_index(struct cache_entry *ce,
+static int locate_in_src_index(const struct cache_entry *ce,
 			       struct unpack_trees_options *o)
 {
 	struct index_state *index = o->src_index;
@@ -388,7 +398,7 @@ static void add_same_unmerged(struct cache_entry *ce,
 static int unpack_index_entry(struct cache_entry *ce,
 			      struct unpack_trees_options *o)
 {
-	struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
+	const struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
 	int ret;
 
 	src[0] = ce;
@@ -590,8 +600,16 @@ static int unpack_nondirectories(int n, unsigned long mask,
 		src[i + o->merge] = create_ce_entry(info, names + i, stage);
 	}
 
-	if (o->merge)
-		return call_unpack_fn(src, o);
+	if (o->merge) {
+		int rc = call_unpack_fn((const struct cache_entry * const *)src,
+					o);
+		for (i = 0; i < n; i++) {
+			struct cache_entry *ce = src[i + o->merge];
+			if (ce != o->df_conflict_entry)
+				free(ce);
+		}
+		return rc;
+	}
 
 	for (i = 0; i < n; i++)
 		if (src[i] && src[i] != o->df_conflict_entry)
@@ -995,7 +1013,9 @@ static void mark_new_skip_worktree(struct exclude_list *el,
 		       select_flag, skip_wt_flag, el);
 }
 
-static int verify_absent(struct cache_entry *, enum unpack_trees_error_types, struct unpack_trees_options *);
+static int verify_absent(const struct cache_entry *,
+			 enum unpack_trees_error_types,
+			 struct unpack_trees_options *);
 /*
  * N-way merge "len" trees.  Returns 0 on success, -1 on failure to manipulate the
  * resulting index, -2 on failure to reflect the changes to the work tree.
@@ -1165,12 +1185,13 @@ return_failed:
 
 /* Here come the merge functions */
 
-static int reject_merge(struct cache_entry *ce, struct unpack_trees_options *o)
+static int reject_merge(const struct cache_entry *ce,
+			struct unpack_trees_options *o)
 {
 	return add_rejected_path(o, ERROR_WOULD_OVERWRITE, ce->name);
 }
 
-static int same(struct cache_entry *a, struct cache_entry *b)
+static int same(const struct cache_entry *a, const struct cache_entry *b)
 {
 	if (!!a != !!b)
 		return 0;
@@ -1187,9 +1208,9 @@ static int same(struct cache_entry *a, struct cache_entry *b)
  * When a CE gets turned into an unmerged entry, we
  * want it to be up-to-date
  */
-static int verify_uptodate_1(struct cache_entry *ce,
-				   struct unpack_trees_options *o,
-				   enum unpack_trees_error_types error_type)
+static int verify_uptodate_1(const struct cache_entry *ce,
+			     struct unpack_trees_options *o,
+			     enum unpack_trees_error_types error_type)
 {
 	struct stat st;
 
@@ -1228,7 +1249,7 @@ static int verify_uptodate_1(struct cache_entry *ce,
 		add_rejected_path(o, error_type, ce->name);
 }
 
-static int verify_uptodate(struct cache_entry *ce,
+static int verify_uptodate(const struct cache_entry *ce,
 			   struct unpack_trees_options *o)
 {
 	if (!o->skip_sparse_checkout && (ce->ce_flags & CE_NEW_SKIP_WORKTREE))
@@ -1236,13 +1257,14 @@ static int verify_uptodate(struct cache_entry *ce,
 	return verify_uptodate_1(ce, o, ERROR_NOT_UPTODATE_FILE);
 }
 
-static int verify_uptodate_sparse(struct cache_entry *ce,
+static int verify_uptodate_sparse(const struct cache_entry *ce,
 				  struct unpack_trees_options *o)
 {
 	return verify_uptodate_1(ce, o, ERROR_SPARSE_NOT_UPTODATE_FILE);
 }
 
-static void invalidate_ce_path(struct cache_entry *ce, struct unpack_trees_options *o)
+static void invalidate_ce_path(const struct cache_entry *ce,
+			       struct unpack_trees_options *o)
 {
 	if (ce)
 		cache_tree_invalidate_path(o->src_index->cache_tree, ce->name);
@@ -1255,16 +1277,16 @@ static void invalidate_ce_path(struct cache_entry *ce, struct unpack_trees_optio
  * Currently, git does not checkout subprojects during a superproject
  * checkout, so it is not going to overwrite anything.
  */
-static int verify_clean_submodule(struct cache_entry *ce,
-				      enum unpack_trees_error_types error_type,
-				      struct unpack_trees_options *o)
+static int verify_clean_submodule(const struct cache_entry *ce,
+				  enum unpack_trees_error_types error_type,
+				  struct unpack_trees_options *o)
 {
 	return 0;
 }
 
-static int verify_clean_subdirectory(struct cache_entry *ce,
-				      enum unpack_trees_error_types error_type,
-				      struct unpack_trees_options *o)
+static int verify_clean_subdirectory(const struct cache_entry *ce,
+				     enum unpack_trees_error_types error_type,
+				     struct unpack_trees_options *o)
 {
 	/*
 	 * we are about to extract "ce->name"; we would not want to lose
@@ -1350,7 +1372,7 @@ static int icase_exists(struct unpack_trees_options *o, const char *name, int le
 }
 
 static int check_ok_to_remove(const char *name, int len, int dtype,
-			      struct cache_entry *ce, struct stat *st,
+			      const struct cache_entry *ce, struct stat *st,
 			      enum unpack_trees_error_types error_type,
 			      struct unpack_trees_options *o)
 {
@@ -1405,9 +1427,9 @@ static int check_ok_to_remove(const char *name, int len, int dtype,
  * We do not want to remove or overwrite a working tree file that
  * is not tracked, unless it is ignored.
  */
-static int verify_absent_1(struct cache_entry *ce,
-				 enum unpack_trees_error_types error_type,
-				 struct unpack_trees_options *o)
+static int verify_absent_1(const struct cache_entry *ce,
+			   enum unpack_trees_error_types error_type,
+			   struct unpack_trees_options *o)
 {
 	int len;
 	struct stat st;
@@ -1440,7 +1462,7 @@ static int verify_absent_1(struct cache_entry *ce,
 	}
 }
 
-static int verify_absent(struct cache_entry *ce,
+static int verify_absent(const struct cache_entry *ce,
 			 enum unpack_trees_error_types error_type,
 			 struct unpack_trees_options *o)
 {
@@ -1449,9 +1471,9 @@ static int verify_absent(struct cache_entry *ce,
 	return verify_absent_1(ce, error_type, o);
 }
 
-static int verify_absent_sparse(struct cache_entry *ce,
-			 enum unpack_trees_error_types error_type,
-			 struct unpack_trees_options *o)
+static int verify_absent_sparse(const struct cache_entry *ce,
+				enum unpack_trees_error_types error_type,
+				struct unpack_trees_options *o)
 {
 	enum unpack_trees_error_types orphaned_error = error_type;
 	if (orphaned_error == ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN)
@@ -1460,10 +1482,12 @@ static int verify_absent_sparse(struct cache_entry *ce,
 	return verify_absent_1(ce, orphaned_error, o);
 }
 
-static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
-		struct unpack_trees_options *o)
+static int merged_entry(const struct cache_entry *ce,
+			const struct cache_entry *old,
+			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
+	struct cache_entry *merge = dup_entry(ce);
 
 	if (!old) {
 		/*
@@ -1481,8 +1505,11 @@ static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 		update |= CE_ADDED;
 		merge->ce_flags |= CE_NEW_SKIP_WORKTREE;
 
-		if (verify_absent(merge, ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o))
+		if (verify_absent(merge,
+				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
+			free(merge);
 			return -1;
+		}
 		invalidate_ce_path(merge, o);
 	} else if (!(old->ce_flags & CE_CONFLICTED)) {
 		/*
@@ -1496,8 +1523,10 @@ static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 			copy_cache_entry(merge, old);
 			update = 0;
 		} else {
-			if (verify_uptodate(old, o))
+			if (verify_uptodate(old, o)) {
+				free(merge);
 				return -1;
+			}
 			/* Migrate old flags over */
 			update |= old->ce_flags & (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
 			invalidate_ce_path(old, o);
@@ -1510,12 +1539,13 @@ static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 		invalidate_ce_path(old, o);
 	}
 
-	add_entry(o, merge, update, CE_STAGEMASK);
+	do_add_entry(o, merge, update, CE_STAGEMASK);
 	return 1;
 }
 
-static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
-		struct unpack_trees_options *o)
+static int deleted_entry(const struct cache_entry *ce,
+			 const struct cache_entry *old,
+			 struct unpack_trees_options *o)
 {
 	/* Did it exist in the index? */
 	if (!old) {
@@ -1530,7 +1560,8 @@ static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
 	return 1;
 }
 
-static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
+static int keep_entry(const struct cache_entry *ce,
+		      struct unpack_trees_options *o)
 {
 	add_entry(o, ce, 0, 0);
 	return 1;
@@ -1552,11 +1583,12 @@ static void show_stage_entry(FILE *o,
 }
 #endif
 
-int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
+int threeway_merge(const struct cache_entry * const *stages,
+		   struct unpack_trees_options *o)
 {
-	struct cache_entry *index;
-	struct cache_entry *head;
-	struct cache_entry *remote = stages[o->head_idx + 1];
+	const struct cache_entry *index;
+	const struct cache_entry *head;
+	const struct cache_entry *remote = stages[o->head_idx + 1];
 	int count;
 	int head_match = 0;
 	int remote_match = 0;
@@ -1641,7 +1673,7 @@ int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
 	if (o->aggressive) {
 		int head_deleted = !head;
 		int remote_deleted = !remote;
-		struct cache_entry *ce = NULL;
+		const struct cache_entry *ce = NULL;
 
 		if (index)
 			ce = index;
@@ -1724,11 +1756,12 @@ int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
  *
  */
-int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o)
+int twoway_merge(const struct cache_entry * const *src,
+		 struct unpack_trees_options *o)
 {
-	struct cache_entry *current = src[0];
-	struct cache_entry *oldtree = src[1];
-	struct cache_entry *newtree = src[2];
+	const struct cache_entry *current = src[0];
+	const struct cache_entry *oldtree = src[1];
+	const struct cache_entry *newtree = src[2];
 
 	if (o->merge_size != 2)
 		return error("Cannot do a twoway merge of %d trees",
@@ -1790,11 +1823,11 @@ int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o)
  * Keep the index entries at stage0, collapse stage1 but make sure
  * stage0 does not have anything there.
  */
-int bind_merge(struct cache_entry **src,
-		struct unpack_trees_options *o)
+int bind_merge(const struct cache_entry * const *src,
+	       struct unpack_trees_options *o)
 {
-	struct cache_entry *old = src[0];
-	struct cache_entry *a = src[1];
+	const struct cache_entry *old = src[0];
+	const struct cache_entry *a = src[1];
 
 	if (o->merge_size != 1)
 		return error("Cannot do a bind merge of %d trees",
@@ -1814,10 +1847,11 @@ int bind_merge(struct cache_entry **src,
  * The rule is:
  * - take the stat information from stage0, take the data from stage1
  */
-int oneway_merge(struct cache_entry **src, struct unpack_trees_options *o)
+int oneway_merge(const struct cache_entry * const *src,
+		 struct unpack_trees_options *o)
 {
-	struct cache_entry *old = src[0];
-	struct cache_entry *a = src[1];
+	const struct cache_entry *old = src[0];
+	const struct cache_entry *a = src[1];
 
 	if (o->merge_size != 1)
 		return error("Cannot do a oneway merge of %d trees",
diff --git a/unpack-trees.h b/unpack-trees.h
index 5e432f576e..36a73a6d00 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -8,7 +8,7 @@
 struct unpack_trees_options;
 struct exclude_list;
 
-typedef int (*merge_fn_t)(struct cache_entry **src,
+typedef int (*merge_fn_t)(const struct cache_entry * const *src,
 		struct unpack_trees_options *options);
 
 enum unpack_trees_error_types {
@@ -77,9 +77,13 @@ struct unpack_trees_options {
 extern int unpack_trees(unsigned n, struct tree_desc *t,
 		struct unpack_trees_options *options);
 
-int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o);
-int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o);
-int bind_merge(struct cache_entry **src, struct unpack_trees_options *o);
-int oneway_merge(struct cache_entry **src, struct unpack_trees_options *o);
+int threeway_merge(const struct cache_entry * const *stages,
+		   struct unpack_trees_options *o);
+int twoway_merge(const struct cache_entry * const *src,
+		 struct unpack_trees_options *o);
+int bind_merge(const struct cache_entry * const *src,
+	       struct unpack_trees_options *o);
+int oneway_merge(const struct cache_entry * const *src,
+		 struct unpack_trees_options *o);
 
 #endif