errors can be in either channel

extract-errors.pl

@@ -0,0 +1,20 @@
+#!/usr/bin/env perl
+my $new_source = "$ENV{source}.new";
+open my $source_in, "<", $ENV{source};
+open my $source_out, ">", $new_source;
+open my $errors, ">>", $ENV{errors};
+my $found_error=0;
+while (<$source_in>) {
+  if ($found_error) {
+    print $errors $_;
+  } elsif (/^error:/) {
+    $found_error=1;
+    print $errors $_;
+  } else {
+    print $source_out $_;
+  }
+}
+close $source_in;
+close $source_out;
+close $errors;
+rename $new_source, $ENV{source};

run-scalafmt.sh

@@ -31,29 +31,8 @@ report() {
 
 errors=$(mktemp)
 
-if grep -q '^error:' "$output"; then
-  output="$output" errors="$errors" perl -e '
-    my $new_output = "$ENV{output}.new";
-    open my $output_in, "<", $ENV{output};
-    open my $output_out, ">", $new_output;
-    open my $errors, ">", $ENV{errors};
-    my $found_error=0;
-    while (<$output_in>) {
-      if ($found_error) {
-        print $errors $_;
-      } elsif (/^error:/) {
-        $found_error=1;
-        print $errors $_;
-      } else {
-        print $output_out $_;
-      }
-    }
-    close $output_in;
-    close $output_out;
-    close $errors;
-    rename $new_output, $ENV{output};
-  '
-fi
+source="$output" errors="$errors" extract-errors.pl
+source="$warnings" errors="$errors" extract-errors.pl
 
 (
     echo "# scalafmt failed ($result)"