Merge branch 'js/maint-merge-use-prepare-commit-msg-hook' into maint

* js/maint-merge-use-prepare-commit-msg-hook:
merge: honor prepare-commit-msg hook

diff --combined builtin/merge.c
index a682043fe5b91317bd7e998fbb95afc9b3ccf368,ca16657d25adde052f728564293294ccca0bfcbe..d534520c3e3e00f148ae3e1267130cd21bdad608
--- 1/builtin/merge.c
--- 2/builtin/merge.c
+++ b/builtin/merge.c
@@@ -194,8 -194,8 +194,8 @@@ static struct option builtin_merge_opti
                "merge strategy to use", option_parse_strategy),
        OPT_CALLBACK('X', "strategy-option", &xopts, "option=value",
                "option for selected merge strategy", option_parse_x),
 -      OPT_CALLBACK('m', "message", &merge_msg, "message",
 -              "message to be used for the merge commit (if any)",
 +      OPT_CALLBACK('m', "message", &merge_msg, "MESSAGE",
 +              "merge commit message (for a non-fast-forward merge)",
                option_parse_message),
        OPT__VERBOSITY(&verbosity),
        OPT_BOOLEAN(0, "abort", &abort_current_merge,
@@@ -795,6 -795,32 +795,32 @@@ static void add_strategies(const char *
  
  }
  
+ static void write_merge_msg(void)
+ {
+       int fd = open(git_path("MERGE_MSG"), O_WRONLY | O_CREAT, 0666);
+       if (fd < 0)
+               die_errno("Could not open '%s' for writing",
+                         git_path("MERGE_MSG"));
+       if (write_in_full(fd, merge_msg.buf, merge_msg.len) != merge_msg.len)
+               die_errno("Could not write to '%s'", git_path("MERGE_MSG"));
+       close(fd);
+ }
+ 
+ static void read_merge_msg(void)
+ {
+       strbuf_reset(&merge_msg);
+       if (strbuf_read_file(&merge_msg, git_path("MERGE_MSG"), 0) < 0)
+               die_errno("Could not read from '%s'", git_path("MERGE_MSG"));
+ }
+ 
+ static void run_prepare_commit_msg(void)
+ {
+       write_merge_msg();
+       run_hook(get_index_file(), "prepare-commit-msg",
+                git_path("MERGE_MSG"), "merge", NULL, NULL);
+       read_merge_msg();
+ }
+ 
  static int merge_trivial(void)
  {
        unsigned char result_tree[20], result_commit[20];
@@@ -806,6 -832,7 +832,7 @@@
        parent->next = xmalloc(sizeof(*parent->next));
        parent->next->item = remoteheads->item;
        parent->next->next = NULL;
+       run_prepare_commit_msg();
        commit_tree(merge_msg.buf, result_tree, parent, result_commit, NULL);
        finish(result_commit, "In-index merge");
        drop_save();
@@@ -835,6 -862,7 +862,7 @@@ static int finish_automerge(struct comm
        }
        free_commit_list(remoteheads);
        strbuf_addch(&merge_msg, '\n');
+       run_prepare_commit_msg();
        commit_tree(merge_msg.buf, result_tree, parents, result_commit, NULL);
        strbuf_addf(&buf, "Merge made by %s.", wt_strategy);
        finish(result_commit, buf.buf);
@@@ -1316,14 -1344,7 +1344,7 @@@ int cmd_merge(int argc, const char **ar
                        die_errno("Could not write to '%s'", git_path("MERGE_HEAD"));
                close(fd);
                strbuf_addch(&merge_msg, '\n');
-               fd = open(git_path("MERGE_MSG"), O_WRONLY | O_CREAT, 0666);
-               if (fd < 0)
-                       die_errno("Could not open '%s' for writing",
-                                 git_path("MERGE_MSG"));
-               if (write_in_full(fd, merge_msg.buf, merge_msg.len) !=
-                       merge_msg.len)
-                       die_errno("Could not write to '%s'", git_path("MERGE_MSG"));
-               close(fd);
+               write_merge_msg();
                fd = open(git_path("MERGE_MODE"), O_WRONLY | O_CREAT | O_TRUNC, 0666);
                if (fd < 0)
                        die_errno("Could not open '%s' for writing",