Merge branch 'jk/format-patch-from' into maint

"format-patch --from=<whom>" forgot to omit unnecessary in-body from
line, i.e. when <whom> is the same as the real author.

* jk/format-patch-from:
  format-patch: print in-body "From" only when needed

cache.h

@@ -966,6 +966,15 @@ struct ident_split {
  */
 extern int split_ident_line(struct ident_split *, const char *, int);
 
+/*
+ * Compare split idents for equality or strict ordering. Note that we
+ * compare only the ident part of the line, ignoring any timestamp.
+ *
+ * Because there are two fields, we must choose one as the primary key; we
+ * currently arbitrarily pick the email.
+ */
+extern int ident_cmp(const struct ident_split *, const struct ident_split *);
+
 struct checkout {
 	const char *base_dir;
 	int base_dir_len;

ident.c

@@ -402,3 +402,32 @@ int git_ident_config(const char *var, const char *value, void *data)
 
 	return 0;
 }
+
+static int buf_cmp(const char *a_begin, const char *a_end,
+		   const char *b_begin, const char *b_end)
+{
+	int a_len = a_end - a_begin;
+	int b_len = b_end - b_begin;
+	int min = a_len < b_len ? a_len : b_len;
+	int cmp;
+
+	cmp = memcmp(a_begin, b_begin, min);
+	if (cmp)
+		return cmp;
+
+	return a_len - b_len;
+}
+
+int ident_cmp(const struct ident_split *a,
+	      const struct ident_split *b)
+{
+	int cmp;
+
+	cmp = buf_cmp(a->mail_begin, a->mail_end,
+		      b->mail_begin, b->mail_end);
+	if (cmp)
+		return cmp;
+
+	return buf_cmp(a->name_begin, a->name_end,
+		       b->name_begin, b->name_end);
+}

pretty.c

@@ -432,7 +432,7 @@ void pp_user_info(struct pretty_print_context *pp,
 		map_user(pp->mailmap, &mailbuf, &maillen, &namebuf, &namelen);
 
 	if (pp->fmt == CMIT_FMT_EMAIL) {
-		if (pp->from_ident) {
+		if (pp->from_ident && ident_cmp(pp->from_ident, &ident)) {
 			struct strbuf buf = STRBUF_INIT;
 
 			strbuf_addstr(&buf, "From: ");

t/t4014-format-patch.sh

@@ -1000,6 +1000,16 @@ test_expect_success '--from uses committer ident' '
 	test_cmp expect patch.head
 '
 
+test_expect_success '--from omits redundant in-body header' '
+	git format-patch -1 --stdout --from="A U Thor <author@example.com>" >patch &&
+	cat >expect <<-\EOF &&
+	From: A U Thor <author@example.com>
+
+	EOF
+	sed -ne "/^From:/p; /^$/p; /^---$/q" <patch >patch.head &&
+	test_cmp expect patch.head
+'
+
 test_expect_success 'in-body headers trigger content encoding' '
 	GIT_AUTHOR_NAME="éxötìc" test_commit exotic &&
 	test_when_finished "git reset --hard HEAD^" &&