"`feed_filename` for default language is specified twice" even though it's not

[Yaroslav-95]

Bug Report

Environment

Zola version: 0.17.2 and master

Expected Behavior

I have set feed_filename to a custom name "feed.xml" in my config.toml at the base or top section of the file, and haven't set it in my default language's section.

On Zola <= 0.17.1 this configuration works and generates a "feed.xml" file under each of the sections where I have generate_feed = true.

Current Behavior

Zola fails to serve or build the site with the following message:

Warning: config.toml contains both default language specific information at base and under section `[languages.en]`, which may cause merge conflicts. Please use only one to specify language specific information
Error: Failed to serve the site
Error: `feed_filename` for default language is specified twice, as "feed.xml" and "atom.xml".

Step to reproduce

Try to build a site with a custom feed_filename set at the top section with multiple languages with no feed_filename in the default language's section.

For an example of such a config.toml: https://git.yaroslavps.com/yaroslavps.com/tree/config.toml

[Keats]

Duplicate of #2360, the issue is the same afaik.

[Yaroslav-95]

I saw that issue but I thought it wasn't related because that one talks about generate_feed and it only results in a warning. I also set generate_feed in my config.toml and there's no problems with it. However, feed_filename generates an error that prevents the site from building.
They do seem quite similar, so most probably you're right they are the same. I'll follow that issue, maybe even try to fix it myself if I find the time.

[Keats]

Re-opening in the meantime until i look at the cause

[SumDonkuS]

Hi,
I saw the other issue was listed as a "good first issue". I'd be excited to help out. I'll just put together a PR here. Please let me know if I am missing anything since this will be my first PR for this project. Thank you again for the great project.