feat: bring up config.updated_option

[SukkaW]

What does it do?

Continuation of #3235, specifically #3235 (comment). #3887 (comment)

Quote from #3887

User may prefer to have full control on value of post.updated and not use file modification time. Currently for my blog, I have to use a new variable lastUpdated as a workaround; since that variable is not recognized by many plugins, I have to fork many plugins.

With this PR, config.optional_updated can be enabled (disabled by default), to leave post.updated to be empty if updated: is not set in the front-matter.

This PR introduced a new option updated_option which accept:

• mtime: This is the default behavior of hexo, use file's mtime as data.updated when not set in front-matter.
• date: Use data.date as data.updated when not set in front-matter.
• empty: Completely remove data.updated when not set in front-matter. This shouldn't be used by common users as it will break many themes (like NexT) and plugins (like hexo-generator-feed)

The use_date_for_updated introduced in hexo v4 is still retained, and still has higher priority than updated_option (That's mean when use_date_for_updated is set to true, updated_option will be ignored).

Breaking changes

See #3887 for more details.

How to test

git clone -b BRANCH https://github.com/USER/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[coveralls]

Coverage increased (+0.08%) to 97.822% when pulling db55fc7 on SukkaW:feat-updated_option into c51b87e on hexojs:master.

[SukkaW]

Without default: moment defined in Post model, the page.updated will no longer exist by default, causing open_graph test case (which is rely on page.updated) to fail.

[curbengh]

Without default: moment defined in Post model, the page.updated will no longer exist by default, causing open_graph test case (which is rely on page.updated) to fail.

Comment out that line and mention this PR.

---

Since the default behavior is still retained, no breaking change then?

[SukkaW]

@curbengh Done.

The PR is now ready for reivew.

[curbengh]

Tested working.

[curbengh]

I re-label this as breaking change due to https://github.com/hexojs/hexo/pull/4278/files#diff-a17a4a3f711955a771f0f61a61525fd9L30, post.updated no longer has a default value and it could be a breaking change for dev that uses Hexo API.