Mini-css-extract-plugin: Asset links broken when extracting CSS and assets to different folders

[andyhall]

• Operating System: OSX
• Node Version: v14.15.4
• NPM Version: 6.14.10
• webpack Version: 5.15.0
• mini-css-extract-plugin Version: ^1.3.5

Expected Behavior

I'm using MiniCssExtractPlugin to extract CSS, and with default settings everything works fine. However I want to export the CSS to its own folder, separate from image assets, like this:

build/styles/bundle.css
build/assets/image.png

Per the docs, I'm doing this by passing a filename option to the plugin with the desired folder name.

Actual Behavior

When I pass in an option like: filename: 'styles/[name].css, the CSS file itself gets exported to the correct directory. However, url(..) asset links inside the CSS aren't adjusted, and wind up broken as a result.

Specifically, styles/bundle.css winds up containing references like url(assets/image.png), causing the browser to request styles/assets/image.png.

Code

The relevant code snippets look like this:

/* webpack.config.js */
    output: {
        filename: 'js/[name].[contenthash:8].js',
        path: path.resolve('.', 'build'),
        publicPath: '',
    },
    plugins: [
        new VueLoaderPlugin(),
        new HtmlWebpackPlugin({ /* .. */ }),
        new MiniCssExtractPlugin({
            filename: 'styles/[name].css' }
        ),
    ],
    module: {
        rules: [
            // ...
            {
                test: /\.png$/,
                type: 'asset/resource',
                generator: { filename: 'assets/[name][ext]' },
            },
            {
                test: /\.css$/,
                use: [ MiniCssExtractPlugin.loader, 'css-loader' ],
            },

/* /src/foo/bar.css */
.whatever {
    background-image: url('~path/to/image.png');
}

After running webpack, the CSS winds up with broken asset links:

/* styles/bundle.css */
.whatever {
    background-image: url('assets/image.png');
        /* should be: url('../assets/image.png') or similar */
}

How Do We Reproduce?

By building a project with configuration as described above (in production mode).

---

Is there some setting or workaround supporting this use case?

Thanks!

[alexander-akait]

Please do not ignore how we can reproduce, sorry won't fix without it, I don't know your output options and how CSS handles, maybe bug in vue-loader, maybe bug in code and resolving options, do you use dev server or just build, I don't know, I will reopen and help you when you fill out ### How Do We Reproduce?

[andyhall]

Hi, I didn't "ignore" the option, I just couldn't think of anything to say there that wasn't already in the other sections. I'll add the info you asked. I'm building normally - I don't know if the issue happens when serving via dev-server, as (per the docs) I don't use CSS extraction in that case.

[alexander-akait]

@andyhall So please provide full configuration and part of code, or better minimum reproducible test repo, I am really want to help, but many issues without good examples and I can't help

[alexander-akait]

Feel free to ping me when it will be ready

[andyhall]

@alexander-akait Sorry, I don't know what you're asking for. The config I posted is already as minimal as I can make it, and it took a fair bit of effort. Are you saying you want the full config I'm using, including everything that isn't related to this issue?

[alexander-akait]

@andyhall I can't reproduce problem with your configuration, so yes, I need fully, you can just create simple reproducible test repo and include part of configuration where the problem reproduced

[alexander-akait]

Why you have publicPath: '',? I think you want publicPath: '/',

[andyhall]

@alexander-akait

Why you have publicPath: '',? I think you want publicPath: '/',

Wouldn't that mean the generated resources will all have hard paths relative to server root? I'm using '' so that resources are linked relative from the html file.

you can just create simple reproducible test repo and include part of configuration where the problem reproduced

For a closed issue?

[alexander-akait]

For a closed issue?

It was closed, because you don't provide enough information to help, if we will keep opened all issues where developers doesn't provide enough formation, here will be trash and will be hard for developers found real problem(s), I will help and/or reopen it if you provide steps to reproduce

[andyhall]

I'm trying in good faith to report an issue. There's no call to be referring to it as trash or not a real problem.

Here is a minimal repro. Config, code, and steps to reproduce are same as posted previously.

[alexander-akait]

I'm trying in good faith to report an issue. There's no call to be referring to it as trash or not a real problem.

I understand you, but try to understand me too, I got very many issues every day and when developer provide only part of code, it requires me to spend efforts on recreating configuration and code to reproduce the problem and most of times not problems (from my experience it is 99% of problems), so other developers won't get help or fixes/features because I will spend most of the time trying to reproduce the problem

[andyhall]

I understand how maintaining works. But if policy for this module is to close any issue without a repo, just say that in the readme or the issue template.

[alexander-akait]

Yep, I will update

[alexander-akait]

I need think about it more, now you can use publicPath: '../', as workaround

[andyhall]

Setting publicPath: '../' only fixes the paths affected by this issue - it breaks the other paths in my project.

[alexander-akait]

@andyhall Yes, in ideal we should https://github.com/webpack/webpack/blob/f9a2c275855027e828983e731ce98189fb7b6d81/lib/util/identifier.js#L311, but we have url only after building, don't have good idea how we can fix it, I need think about it...

Note for me:
Other example https://github.com/xenobytezero/sass-loader-github-bug

[andyhall]

@alexander-akait Take your time, there's no rush. I'm already working around the issue myself; I only posted this issue for others who might encounter it.

[karlvr]

I believe I am having the same issue... I am including .less files in a JavaScript component; the .less file is in a path ./js/components/less/example.less and it references the image as url(../../../img/example.jpg). My publicPath option to the MiniCssExtractPlugin loader is return path.relative(path.dirname(resourcePath), context) + '/', and I end up url(../../../img/example.jpg) in the output CSS.

However, because the component that's including the less is getting included from a file in ./js/example.js, that relative path is no longer accurate. It seems that MiniCssExtractPlugin knows the filename of the eventual output (using the filename option). I am going to look into this issue as well to see if it's something I can improve.

[karlvr]

It seems that we should be able to compute a relative path in renderContentAsset based on the context of the CssModule and the path that we're rendering the chunk to... by passing that info for each url out to a helper function, like the publicPath one...

[alexander-akait]

If somebody have solutions right now, feel free to send a PR

[karlvr]

Working on it. I must say it's hard to get ones head around publicPath in all its ways!

I have something that works for me... I'm wondering if it will do the trick for everyone.

MiniCSSExtractPlugin currently supports the publicPath = "auto" by simply setting publicPath = "". I wonder if that's intentional or because there was no better solution. The docs suggest that "auto" means that publicPath will be automatically determined. I'm hoping that setting it to "" means we have ¯_(ツ)_/¯ed here, and therefore my solution co-opts "auto" in the hopes that it then also becomes default behaviour and just does the right thing!

My solution sets publicPath = "'/__MINI_CSS_EXTRACT_PLUGIN__/'" when the publicPath option is set to "auto", and then we replace that in the plugin at which point we know the context-relative path of the output file.

In renderContentAsset(compiler, compilation, chunk, modules, requestShortener) we add:

const publicPath = path.relative(path.dirname(chunk.name), "");
content = content.replace(/\/__MINI_CSS_EXTRACT_PLUGIN__/g, publicPath);

So now the "auto" mode means that we compute a relative path from our output file to the publicPath / root and then use that for each asset in our output CSS.

I'm going to prepare a PR. I'd love some feedback if this approach seems suitable.

[karlvr]

I've also published a test module that we're using internally at https://npmjs.com/@cactuslab/mini-css-extract-plugin that might be the easiest way to test if this resolves your issue @andyhall

[andyhall]

@karlvr I tried your plugin in my reproducing repo, but webpack's output didn't change at all. Was I supposed to do something besides swapping the main plugin for yours?

[karlvr]

@andyhall do you have publicPath set to anything? And what version of Webpack are you using? I am using 5. If you're using 4, please try setting publicPath to "auto" in the loader options for mini-css-extract-plugin.

[andyhall]

@karlvr I'm building the minimal-reproduction repo linked up-thread. Versions and settings are in the repo.

Edit: in that repo I swapped the plugin module to yours, and tried building with and without the publicPath: 'auto' setting, but webpack's CSS output didn't change.

[karlvr]

@andyhall thanks Andy... I have reproduced the fault in your minimal repo. I made some assumptions about the chunk name and that it would reflect where the output was going. It does in my case as I use a relative filename for my outputs...

So, all we need to know is where we're planning to write the file that we're outputting. Is that possible?

[karlvr]

@andyhall OK, please upgrade to 1.3.10 of @cactuslab/mini-css-extract-plugin. This now looks at the output filename template to work out any additional relative paths to consider. In your case, that is styles/[name].css so we get an extra ../ which is what we need.

In order to make it work with your repo I removed the publicPath line from webpack.config.js (as "auto" is the default), upgraded the plugin, and updated the require statement in webpack.config.js, then ran npm run build.

I am really straying into an area of interacting with the webpack API that I'm not at all familiar with. I hope there's a function to render a filename template given a chunk... I've just regexed the name into the template in case the name contains path components!

[andyhall]

@karlvr Is removing publicPath required for your fix to work?

I tried the steps you suggested and they fix the CSS link, but per the original post, publicPath: '' is part of the repro steps for this issue. Removing it breaks other stuff in my actual project.

(I could be missing something, I don't know anything about webpack internals and wasn't able to follow what your fix is doing.)

[karlvr]

@andyhall Good question. Removing publicPath (which sets it to its default in Webpack 5, which is now "auto") is what my patch currently uses to activate its changes. But I guess the same fix is required for any relative publicPath.

What is the intended meaning of setting publicPath to ""? Could you detail what breaks in your project when projectPath is "auto" instead?

Anyway… it would be possible to activate this patch on _any_ relative publicPath including "". We know where the .css file is output so we can always compute a relative path to the root of the context. In fact we don't _ever_ even _need_ publicPath. Maybe our thinking changes to "we'll use publicPath only if it's absolute, otherwise we can compute a relative path easily thank you very much, and relative paths _always_ work consistently in CSS files, relative to the CSS file itself"

Super easy to change the patch to this way of thinking. Is it too much or flawed @alexander-akait? I'm starting to think it's actually essential.

[alexander-akait]

Anyway… it would be possible to activate this patch on any relative publicPath including "". We know where the .css file is output so we can always compute a relative path to the root of the context. In fact we don't ever even need publicPath. Maybe our thinking changes to "we'll use publicPath only if it's absolute, otherwise we can compute a relative path easily thank you very much, and relative paths always work consistently in CSS files, relative to the CSS file itself"

You are right here, in long term we should avoid using publicPath, you need specify it only when you need absolute urls, like CDN or specific env.

[karlvr]

@alexander-akait Perhaps a good first step is to take publicPath values "auto" and "" and "take over" and compute the relative URL ourselves, and see where that leads? I think that's what I've done in the PR... I'll try to improve the applying of the template this week.

[andyhall]

What is the intended meaning of setting publicPath to ""?

you need specify it only when you need absolute urls, like CDN or specific env

Hi, just to clarify here I'm using publicPath: '' to mean that linked assets should be linked relative to the location of the html file loading them, not from a CDN/etc. The intention is that if you build the repo I posted, the contents of the build folder could then be copied into any directory on a server.

[alexander-akait]

publicPath: '' and publicPath: 'auto' is not the same, publicPath: 'auto' should do relative assets, publicPath: '' is just empty publicPath

[karlvr]

@andyhall removing publicPath or setting it to auto will achieve what you want to achieve. We have to do _something_ in order to make the uris to assets correct in the CSS we output, so I've just pushed a patch that treats publicPath '' in the same way, and I believe it will achieve what you want to achieve.

@andyhall you mention that removing publicPath (effectively setting it to 'auto' on webpack 5) breaks other things. Would you be able to provide details of the other things it breaks? I think that would help me, at least, understand how best to resolve it here.

Also, please upgrade to @cactuslab/[email protected] as I have included the patch to handle the '', and please let me know if this now has your whole webpack project working.

[andyhall]

Hi @karlvr , regarding "removing publicPath will achieve what you want to achieve", I don't know what you mean. Having publicPath: '' is part of the config for my project, separate from the issue we're talking about here.

However with that said, using the 1.3.11 version with my current config appears to fix the issue for me. I can extract the CSS output into a folder, and url(..) links in the CSS are no longer broken. I have no idea about the inner workings, but outwardly LGTM!

[alexander-akait]

Yep, it is good fix, need couple test and we can merge it

[karlvr]

publicPath: '' and publicPath: 'auto' is not the same, publicPath: 'auto' should do relative assets, publicPath: '' is just empty publicPath

Yes, that's literally absolutely correct, however I think the intention of the two is the same. I think webpack 5 just made it explicit. The default was empty; the default is now auto.

An empty publicPath is broken for CSS when the CSS is located out of the root. But people expect it to work as I think they want it to mean "use relative paths and make it work", which I think is synonymous with auto.

That's why I'm curious what breaks by adopting publicPath auto (or removing publicPath and thus using the default value of auto). My expectation is that everything just works, and where it doesn't there lie more bugs to fix!

[alexander-akait]

Anyway, can you add couple tests for your PR?

[devthiagocaetano]

@andyhall OK, please upgrade to 1.3.10 of @cactuslab/mini-css-extract-plugin. This now looks at the output filename template to work out any additional relative paths to consider. In your case, that is styles/[name].css so we get an extra ../ which is what we need.

In order to make it work with your repo I removed the publicPath line from webpack.config.js (as "auto" is the default), upgraded the plugin, and updated the require statement in webpack.config.js, then ran npm run build.

This worked for me!! Thanks a lot 🇧🇷
obs: I never used publicPath, so just installed the npm package and changed the require.

@karlvr When I added filename: 'assets/css/[name].css', in MiniCssExtractPlugin (wich refers to yours), my dist css looses the images again. Is there a way to work around this??
I can give u more infos, but you guys have done a great job so far, and I don't want to waste your time on this if would be unnecessary