filter-repo: only set author from committer if author email not set

Some commits may have a valid author email, but no valid author name.
Old versions of git didn't enforce a non-empty name.
Setting the author data from the committer is wrong in this case.

Also add a test case for this to t9390.

Example: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c6295cdf656de63d6d1123def71daba6cd91939c

(en: replaced with a dedicated test instead of tweaking existing ones)

Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Elijah Newren <newren@gmail.com>

git-filter-repo

@@ -1189,13 +1189,14 @@ class FastExportParser(object):
       original_id = self._parse_original_id();
 
     author_name = None
+    author_email = None
     if self._currentline.startswith(b'author'):
       (author_name, author_email, author_date) = self._parse_user(b'author')
 
     (committer_name, committer_email, committer_date) = \
       self._parse_user(b'committer')
 
-    if not author_name:
+    if not author_name and not author_email:
       (author_name, author_email, author_date) = \
         (committer_name, committer_email, committer_date)
 

t/t9390-filter-repo.sh

@@ -1649,4 +1649,37 @@ test_expect_success '--version' '
 	test_cmp expect actual
 '
 
+test_expect_success 'empty author ident' '
+	test_create_repo empty_author_ident &&
+	(
+		cd empty_author_ident &&
+
+		git init &&
+		cat <<-EOF | git fast-import --quiet &&
+			feature done
+			blob
+			mark :1
+			data 8
+			initial
+
+			reset refs/heads/develop
+			commit refs/heads/develop
+			mark :2
+			author <empty@ident.ity> 1535228562 -0700
+			committer Full Name <email@add.ress> 1535228562 -0700
+			data 8
+			Initial
+			M 100644 :1 filename
+
+			done
+			EOF
+
+		git filter-repo --force --path-rename filename:stuff &&
+
+		git log --format=%an develop >actual &&
+		echo >expect &&
+		test_cmp expect actual
+	)
+'
+
 test_done