问题

I am facing a problem in Webpack regarding Relative Path. Let me try to explain the scenario :

I have 2 separate project in Workspace directory :

Project-A [Bundling using Gulp] : Stable & Working
Project-B [Bundling using Webpack] : New project

As both the projects are using same Styling, so I wanted to reuse the SCSS files [consisting of standard variables, predefined layouts, modals, classes etc] of Project A into Project B.

Now, if I am trying to import Project-A index.scss in Project-B index.scss as another partial [Commenting out the Background Image URL Depency], webpack is able to generate the required CSS output file.

// Import Project A SCSS [Common Varibles, Classes, Styling etc] 
@import "../../../../Project_A/assets/stylesheets/index";

But as Project-A's index.scss is further referring background images from the respective Relative-Path, the webpack build is throwing error

'File / dir not found in XYZ/Project-B/Source/Stylesheets'.

Exact Error Block :

ERROR in ./src/assets/stylesheets/index.scss Module build failed: ModuleNotFoundError: Module not found: Error: Cannot resolve 'file' or 'diWorkSpace\Project_B\src\assets\stylesheets

screenshot :

I am not able to understand, why Webpack is not able to resolve the Relative path of assets inside Project-A and still looking inside 'Project B'.

Here is the Code-Repo URL for the simulated issue : https://github.com/raviroshan/webpack-build-issue/tree/master/WorkSpace

Steps to reproduce.

Download the Repo.
Browse inside Project_B folder, and do a NPM install.
Run 'webpack'. It would build correctly as Relative Image URL code is commented out.
Now put back the commented line of code : https://github.com/raviroshan/webpack-build-issue/blob/master/WorkSpace/Project_A/assets/stylesheets/index.scss#L27

回答1:

So, finally after so much struggle, got a proper SOLUTION.

It turns out to be an issue with CSS-loader i.e it is not able to resolve the URL with respective to current file.

Using resolve-url-loader solved this problem. https://www.npmjs.com/package/resolve-url-loader

 // Old Loader Config in Webpack-entry
 loader: ExtractTextPlugin.extract('style-loader', 'css-loader?sourceMap!sass-loader?sourceMap')

 // New [Fixed] Loader Config in Webpack-entry
 loader: ExtractTextPlugin.extract('style-loader', 'css-loader?sourceMap!resolve-url-loader!sass-loader?sourceMap')

Here is updated Code-Repo with solution : https://github.com/raviroshan/webpack-build-issue

Note : Don't omit -loader Your Webpack.config.js should always use the long-form of the loader name (i.e. the -loader suffix).

There is another package called resolve-url which Webpack can confuse with resolve-url-loader.

回答2:

It seems like it's css-loader fault and the way it resolves paths in @import and url(). It tries to resolve all paths — even those from imported stylesheets — relative to the main CSS file — which in your case is /Project_B/src/assets/stylesheets/index.scss.

Don't cry! There's a solution!

Maybe it's not perfect, but it's the best one I came with so far.

Create a global variable $assetsPath holding a path to assets relative to the current stylesheet. Then prepend this variable to all your url() values.

In your /Project_A/assets/stylesheets/index.scss you'd write:

/*/ Using !default we can override this variable even before the following line: /*/
$assetsPath: '../' !default;

.container {
    /*/ ... /*/
    .content-wrapper {
        /*/ ... /*/
        background-image: url($assetsPath + "images/content-bg.jpg");
    }
}

In your /Project_B/src/assets/stylesheets/index.scss you'd write:

/*/ The following variable will override $assetsPath defined in the imported file: /*/
$assetsPath: '../../../../Project_A/assets/';

/*/ Import Project A SCSS [Common Varibles, Classes, Styling etc] /*/
@import "../../../../Project_A/assets/stylesheets/index";

The Aftermath

If you bundle Project-A with Gulp it's gonna see Project-A's code as:

        /*/ ... /*/
        background-image: url("../images/content-bg.jpg");

Although, when you bundle Project-B with Webpack it's gonna see Project-A's code as:

        /*/ ... /*/
        background-image: url("../../../../Project_A/assets/images/content-bg.jpg");

Therefore, you are saved.

Most definitely I'll look closer at this issue. All of this could be avoided if url-loader would respect a path in the @import statement and apply it to referenced assets accordingly. Either I'm missing something or it should be considered as a bug.

I hope you have a wonderful day!
~Wiktor