Merge branch 'nd/maint-branch-desc-doc'

Teach various forms of "format-patch" command line to identify what
branch the patches are taken from, so that the branch description
is picked up in more cases.

* nd/maint-branch-desc-doc:
  format-patch: pick up branch description when no ref is specified
  format-patch: pick up correct branch name from symbolic ref
  t4014: a few more tests on cover letter using branch description
  branch: delete branch description if it's empty
  config.txt: a few lines about branch.<name>.description

Documentation/config.txt

@@ -739,6 +739,12 @@ branch.<name>.rebase::
 it unless you understand the implications (see linkgit:git-rebase[1]
 for details).
 
+branch.<name>.description::
+	Branch description, can be edited with
+	`git branch --edit-description`. Branch description is
+	automatically added in the format-patch cover letter or
+	request-pull summary.
+
 browser.<tool>.cmd::
 	Specify the command to invoke the specified browser. The
 	specified command is evaluated in shell with the URLs passed

builtin/branch.c

@@ -725,7 +725,7 @@ static int edit_branch_description(const char *branch_name)
 	stripspace(&buf, 1);
 
 	strbuf_addf(&name, "branch.%s.description", branch_name);
-	status = git_config_set(name.buf, buf.buf);
+	status = git_config_set(name.buf, buf.len ? buf.buf : NULL);
 	strbuf_release(&name);
 	strbuf_release(&buf);
 

builtin/log.c

@@ -1016,8 +1016,9 @@ static char *find_branch_name(struct rev_info *rev)
 {
 	int i, positive = -1;
 	unsigned char branch_sha1[20];
-	struct strbuf buf = STRBUF_INIT;
-	const char *branch;
+	const unsigned char *tip_sha1;
+	const char *ref;
+	char *full_ref, *branch = NULL;
 
 	for (i = 0; i < rev->cmdline.nr; i++) {
 		if (rev->cmdline.rev[i].flags & UNINTERESTING)
@@ -1027,18 +1028,27 @@ static char *find_branch_name(struct rev_info *rev)
 		else
 			return NULL;
 	}
-	if (positive < 0)
+	if (0 <= positive) {
+		ref = rev->cmdline.rev[positive].name;
+		tip_sha1 = rev->cmdline.rev[positive].item->sha1;
+	} else if (!rev->cmdline.nr && rev->pending.nr == 1 &&
+		   !strcmp(rev->pending.objects[0].name, "HEAD")) {
+		/*
+		 * No actual ref from command line, but "HEAD" from
+		 * rev->def was added in setup_revisions()
+		 * e.g. format-patch --cover-letter -12
+		 */
+		ref = "HEAD";
+		tip_sha1 = rev->pending.objects[0].item->sha1;
+	} else {
 		return NULL;
-	strbuf_addf(&buf, "refs/heads/%s", rev->cmdline.rev[positive].name);
-	branch = resolve_ref_unsafe(buf.buf, branch_sha1, 1, NULL);
-	if (!branch ||
-	    prefixcmp(branch, "refs/heads/") ||
-	    hashcmp(rev->cmdline.rev[positive].item->sha1, branch_sha1))
-		branch = NULL;
-	strbuf_release(&buf);
-	if (branch)
-		return xstrdup(rev->cmdline.rev[positive].name);
-	return NULL;
+	}
+	if (dwim_ref(ref, strlen(ref), branch_sha1, &full_ref) &&
+	    !prefixcmp(full_ref, "refs/heads/") &&
+	    !hashcmp(tip_sha1, branch_sha1))
+		branch = xstrdup(full_ref + strlen("refs/heads/"));
+	free(full_ref);
+	return branch;
 }
 
 int cmd_format_patch(int argc, const char **argv, const char *prefix)

t/t4014-format-patch.sh

@@ -963,4 +963,46 @@ test_expect_success 'format patch ignores color.ui' '
 	test_cmp expect actual
 '
 
+test_expect_success 'cover letter using branch description (1)' '
+	git checkout rebuild-1 &&
+	test_config branch.rebuild-1.description hello &&
+	git format-patch --stdout --cover-letter master >actual &&
+	grep hello actual >/dev/null
+'
+
+test_expect_success 'cover letter using branch description (2)' '
+	git checkout rebuild-1 &&
+	test_config branch.rebuild-1.description hello &&
+	git format-patch --stdout --cover-letter rebuild-1~2..rebuild-1 >actual &&
+	grep hello actual >/dev/null
+'
+
+test_expect_success 'cover letter using branch description (3)' '
+	git checkout rebuild-1 &&
+	test_config branch.rebuild-1.description hello &&
+	git format-patch --stdout --cover-letter ^master rebuild-1 >actual &&
+	grep hello actual >/dev/null
+'
+
+test_expect_success 'cover letter using branch description (4)' '
+	git checkout rebuild-1 &&
+	test_config branch.rebuild-1.description hello &&
+	git format-patch --stdout --cover-letter master.. >actual &&
+	grep hello actual >/dev/null
+'
+
+test_expect_success 'cover letter using branch description (5)' '
+	git checkout rebuild-1 &&
+	test_config branch.rebuild-1.description hello &&
+	git format-patch --stdout --cover-letter -2 HEAD >actual &&
+	grep hello actual >/dev/null
+'
+
+test_expect_success 'cover letter using branch description (6)' '
+	git checkout rebuild-1 &&
+	test_config branch.rebuild-1.description hello &&
+	git format-patch --stdout --cover-letter -2 >actual &&
+	grep hello actual >/dev/null
+'
+
 test_done