commit: fix patch hunk editing with "commit -p -m"

Don't change git environment: move the GIT_EDITOR=":" override to the
hook command subprocess, like it's already done for GIT_INDEX_FILE.

Signed-off-by: Benoit Pierre <benoit.pierre@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/commit.c b/builtin/commit.c
index 3767478..baf1fc0 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -612,7 +612,7 @@
 	/* This checks and barfs if author is badly specified */
 	determine_author_info(author_ident);
 
-	if (!no_verify && run_hook(index_file, "pre-commit", NULL))
+	if (!no_verify && run_commit_hook(use_editor, index_file, "pre-commit", NULL))
 		return 0;
 
 	if (squash_message) {
@@ -866,8 +866,8 @@
 		return 0;
 	}
 
-	if (run_hook(index_file, "prepare-commit-msg",
-		     git_path(commit_editmsg), hook_arg1, hook_arg2, NULL))
+	if (run_commit_hook(use_editor, index_file, "prepare-commit-msg",
+			    git_path(commit_editmsg), hook_arg1, hook_arg2, NULL))
 		return 0;
 
 	if (use_editor) {
@@ -883,7 +883,7 @@
 	}
 
 	if (!no_verify &&
-	    run_hook(index_file, "commit-msg", git_path(commit_editmsg), NULL)) {
+	    run_commit_hook(use_editor, index_file, "commit-msg", git_path(commit_editmsg), NULL)) {
 		return 0;
 	}
 
@@ -1067,8 +1067,6 @@
 		use_editor = 0;
 	if (0 <= edit_flag)
 		use_editor = edit_flag;
-	if (!use_editor)
-		setenv("GIT_EDITOR", ":", 1);
 
 	/* Sanity check options */
 	if (amend && !current_head)
@@ -1445,6 +1443,29 @@
 	return finish_command(&proc);
 }
 
+int run_commit_hook(int editor_is_used, const char *index_file, const char *name, ...)
+{
+	const char *hook_env[3] =  { NULL };
+	char index[PATH_MAX];
+	va_list args;
+	int ret;
+
+	snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
+	hook_env[0] = index;
+
+	/*
+	 * Let the hook know that no editor will be launched.
+	 */
+	if (!editor_is_used)
+		hook_env[1] = "GIT_EDITOR=:";
+
+	va_start(args, name);
+	ret = run_hook_ve(hook_env, name, args);
+	va_end(args);
+
+	return ret;
+}
+
 int cmd_commit(int argc, const char **argv, const char *prefix)
 {
 	static struct wt_status s;
@@ -1669,7 +1690,7 @@
 		     "not exceeded, and then \"git reset HEAD\" to recover."));
 
 	rerere(0);
-	run_hook(get_index_file(), "post-commit", NULL);
+	run_commit_hook(use_editor, get_index_file(), "post-commit", NULL);
 	if (amend && !no_post_rewrite) {
 		struct notes_rewrite_cfg *cfg;
 		cfg = init_copy_notes_for_rewrite("amend");