fix(#1490): if post_asset_folder is set, restrict renderable files to default file extension

[kristofzerbe]

What does it do?

It alleviates the problem on the rendering asset files as posts, if post_asset_folder is set to true, by restricting the rendered file types to the default new post type (new_post_name).

Caveat: Doesn't work with MD files as assets, when your default file type is MD.

It is not a final solution, as it would be better to identify to subfolder as asset folder in this stage of code execution.

How to test

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

1. Set post_asset_folder to true in _config.yml
2. Create new post
3. Create subfolder (without leading underscore!) in newly created asset folder for the post
4. Copy a HTML, JS or CSS file into the subfolder
5. run hexo generate

None of the subfolders files should be rendered as post, as it will be in the current version. They will be treated as real assets.

[SukkaW]

LGTM!

Would you mind adding unit test cases for the changes as well?

[tomap]

@SukkaW maybe we could add the unit tests ourselves (@hexojs/core ) and fix the linting issue to move forward faster?

[SukkaW]

@SukkaW maybe we could add the unit tests ourselves (@hexojs/core ) and fix the linting issue to move forward faster?

Yeah, that would be fine.

[yoshinorin]

@kristofzerbe
Thank you :)

@hexojs/core
I wrote the test code & fix lint.
Would you please review again?

Thank you :)

[kristofzerbe]

Thank you for the test and lint... Happy New Year