feat(load_theme_config): support alternate theme config

[SukkaW]

What does it do?

The part of #3890

theme_config in _config.yml looks good, but it is better to have a separate theme config. We could introduce _config.[name].yml. Currently, theme_config has higher priority than _config.yml under theme directories. After bring up _config.[name].yml, I suggest the theme_config in _config.yml > _config.[name].yml > _config.yml under theme directories which will retain highest priority for theme_config.

How to test

git clone -b theme-config-dedicated https://github.com/sukkaw/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

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

[yoshinorin]

Is this feature will allow other than YAML format?

[SukkaW]

Since I just port the feature from load_config, if Hexo support _config.json, then _config.test_theme.json should be supported as well (That's why I include this in test cases)

[stevenjoezhang]

Currently theme_config only affects template local

hexo/lib/hexo/index.js

Line 360 in 6d29793

theme.config = deepMerge(theme.config, config.theme_config);

Which means something like

hexo.extend.filter.register('', () => {
  let { key } = hexo.theme.config;
  // If the key is defined in `theme_config`, it would be null here
}, 0);

does not work.

Is it possible to merge config.theme_config into theme.config after ctx.theme loads?

See also iissnan/hexo-theme-next#328 ink-zone/fexo#157

Update: #4360