fix: compatibility with existing theme

[curbengh]

Fixes #112

Existing theme expects feed.path to be a string, but previous PR #96 converts it to array. This PR prevents the conversion.

cc @mikolaje @yrpang @AlynxZhou @stevenjoezhang

[coveralls]

Coverage remained the same at 100.0% when pulling 0314e98 on curbengh:theme-compat into 9f1f7b0 on hexojs:master.

[SukkaW]

Should we fix #115 in this PR as well? We could create a ctx instead of writing new syntax of config back to hexo.

[curbengh]

This PR also fixes #115.

This plugin needs to write back to user config to ensure consistency. If it is not consistent, it can break this feature especially this line.

[curbengh]

Whether or not this plugin should write back to user config actually doesn't matter, because a theme still need

    <% if (config.feed) { %>
      <% if (config.feed.type.length && config.feed.path.length) { %>
        <% if (typeof config.feed.type === 'string' )) { %>
          <link rel="alternate" type="application/<%- config.feed.type.replace(/2$/, '') %>+xml" title="<%= config.title %>" href="<%- url_for(config.feed.path) %>">
        <% } else { %>
          <% for (const i in config.feed.type) { %>
            <link rel="alternate" type="application/<%- config.feed.type[i].replace(/2$/, '') %>+xml" title="<%= config.title %>" href="<%- url_for(config.feed.path[i]) %>">
          <% } %>
        <% } %>
      <% } %>
    <% } %>

to be compatible with both #100 (released in 2.1) and older versions of this plugin.

[stevenjoezhang]

We have noticed this problem about the type of feed.path: theme-next/hexo-theme-next@c78f3ab
This Pull Request will be very helpful, thanks!

[curbengh]

We have noticed this problem about the type of feed.path: theme-next/hexo-theme-next@c78f3ab

cc @mikolaje

---

@stevenjoezhang
But theme-next/hexo-theme-next@c78f3ab is still not compatible with #100 though.

I also noticed the theme doesn't support RSS2 format. Relevant PR yscoder/hexo-theme-indigo#489.

[stevenjoezhang]

I will do some research. Compatibility with these core plugins of Hexo is critical to a theme.

[curbengh]

@hexojs/core this is an urgent fix.