Incorporate linkPrefix into webpack's publicPath

[mojodna]

This correctly references asset paths, e.g. FontAwesome, when static sites are targeted at sub-paths.

Prior to this, FontAwesome asset paths would point at the site root.

[KyleAMathews]

@mojodna does this work? @tribou tried this before and ran into problems... #393

Also for a PR like this, you need to check if prefixing links is active similar to what I've done on the 1.0 branch

gatsby/lib/utils/webpack.config.js

Line 47 in bc9f926

publicPath: program.prefixLinks ? `${siteDB().get(`config`).linkPrefix}/` : `/`,

[mojodna]

Err, maybe not. Sounds like I fell into the same trap. Here's my app-land workaround: https://github.com/mojodna/posm-admin-ii/blob/master/gatsby-node.js#L16-L22

[KyleAMathews]

Oh nice! That's perfect. Would love it if you pushed that into the PR. This is a fairly common problem right now so it'd be good to get it fixed.

[mojodna]

Maybe it belongs in the starter packs instead, or in the meantime?

Might be worth documenting it (though maybe the issues suffice), since I expect others may also spend hours trying to understand why things aren't working before realizing that it's actually a webpack configuration problem.

[KyleAMathews]

Why not in core? AFAIK the webpack publicPath should always be / or /my-site-prefix/.

[mojodna]

Oh, core would be ideal, but if it's not feasible...

I'll take another whack at this, but it'll be a few days before I'm able.

[KyleAMathews]

Yeah it should totally be possible. The only problem with your's and @tribou's PR is requiring config.toml doesn't work as that's a Webpack thing. If you do what you did in your site it'll work just fine.

[mojodna]

@KyleAMathews I just pushed a replacement commit that uses toml to load the config and works when linked into a project that uses gatsby.

[KyleAMathews]

Awesome thanks! Will add this to a release in a jiffy.

[jlengstorf]

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