Issue with Dotless MVC bundling occurring when attempting to import a specific less file multiple times

Trying to achieve a specific structure using dotless:

styles/variables.less - contains all variables like this

@color:green;



styles/component1.less - random component specific style importing variables.less

@import "variables";

body {
   background:@color;
}



styles/component2.less - more styles importing global variables.less file

@import "variables";

a {
    color:@color;
}



BundleConfig.cs - bundle declaration as follows using a bundling addition: https://gist.github.com/benfoster/3924025

bundles.Add(new Bundle("~/styles/css", new LessTransform()).Include("~/styles/component1.less", "~/styles/component2.less"));



Works fine when Debug is true

However, when Debug is false

Only the first file included in the bundle's Include method recognizes @import "variables". The rest fail.

Output when declaring "~/styles/component1.less" first

bundles.Add(new Bundle("~/styles/css", new LessTransform()).Include("~/styles/component1.less", "~/styles/component2.less"));


Output when declaring "~/styles/component2.less" first

bundles.Add(new Bundle("~/styles/css", new LessTransform()).Include("~/styles/component2.less", "~/styles/component1.less"));

Interestingly, it works if different files are imported in component1 and component2

For example, renaming "varibales" to "variables.less" in one file to differentiate the imports.

styles/component1.less

@import "variables.less"; // added extension here

body {
   background:@color;
}

Any ideas? Been working on this for days..

Edit

Reasons for using this structure:

  • To separate less files in debug mode for easier debugging. Line number comments are not very helpful.

  • To concatenate and minify all less files for production.

Adding @import "variables" to every file is not ideal.

Tried including variables.less in .Include("variables.less", file-dependant-on-variables.less, ...) However, it does not work due to scoping issues mentioned here: Dotless - Can't reference less variable in separate file with MVC Bundling

A solution is concatenating the contents of every less file and parsing that concatenated file with Less. Find an example here: https://groups.google.com/forum/?fromgroups#!topic/dotless/j-8OP1dNjUY

However, in that case, a minified version of the parsed file seems unattainable.

Answer №1

As stated in the documentation:

Between versions 1.3.0 and 1.3.3, the @import function imported a file multiple times, with the option to override this behavior using @import-once.

However, in version 1.4.0, @import-once was removed and @import now imports a file only once by default. This can lead to variables being ignored in subsequent imports, potentially causing rules or even the entire Less file to be disregarded.

To address this issue, importing variables at a higher level, as suggested by @Hans, can resolve the problem (+1). Alternatively, reverting to an earlier version of the preprocessor (1.3.0 - 1.3.3) where @import behaves differently may also be a viable solution.

Answer №2

It appears that there may be a solution that I am overlooking as you have not provided the reason behind your aim to achieve this particular structure. However, a simple way to address the issue and reduce the resulting bundle size is by reorganizing your file structure. To do this, create a separate less file containing the following:

@import "variables.less";
@import "component1.less";
@import "component2.less";

Include this new file in the bundler. By doing so, the bundle size will be smaller because variables.less is only included once instead of twice. This approach is compatible with Dotless and should effectively resolve the issue.

Answer №3

It's clear that @o.v. is correct. While parsing the second .less file in the bundle, Dotless encounters the following error:

The variable @color is not defined on line 4 in the file

'..\styles\component2.less':

[3]: a { [4]: color:@color;

   ----------^

If you delve into the Dotless sources, you'll come across the CheckIgnoreImport method within the dotless.Core.Importers.Importer class. This method is invoked for each imported file:

/// <summary>
///  returns true if the import should be ignored because it is a duplicate and import-once was used
/// </summary>
/// <param name="import"></param>
/// <returns></returns>
protected bool CheckIgnoreImport(Import import, string path)
{
    if (_rawImports.Contains(path, StringComparer.InvariantCultureIgnoreCase))
    {
        return import.IsOnce;
    }
    _rawImports.Add(path);

    return false;
}

At present, the value of import.IsOnce is always set to true (refer to the dotless.Core.Parser.Parsers class, line 1080). Unfortunately, there is no way to alter this behavior externally to the Dotless library.

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