Metadata file parse errors cause silent failure?

[wlupton]

Apologies if this is known and has already been fixed. It seems that if there are errors in supplied metadata files then the errors aren't reported, the metadata in the file is ignored (or perhaps only that as-yet unparsed; not sure) and processing proceeds.

In the example below, you can see that title must be being ignored in the first case.

lewa:pandoc% pandoc --version
pandoc 2.9.2.1

lewa:pandoc% cat bad.yaml 
var: This: has: colons:
title: This should be the title

lewa:pandoc% cat good.yaml 
var: 'This: has: colons:'
title: This should be the title

lewa:pandoc% cat document.md
This is a document.

lewa:pandoc% pandoc --standalone --metadata-file bad.yaml document.md --output document.html
[WARNING] This document format requires a nonempty <title> element.
  Defaulting to 'document' as the title.
  To specify a title, use 'title' in metadata or --metadata title="...".

lewa:pandoc% pandoc --standalone --metadata-file good.yaml document.md --output document.html