inject_assets_builder 1.0.0+1

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A builder that makes it possible for a package to access files from packages depending on it.

inject assets builder #

Build Status

This package contains a builder that makes it possible for a package to access files from packages depending on it.

The build package uses the syntax pkg|lib/foo.txt to refer to the file foo.txt in the lib/ directory of package pkg. In this document, I'll use the same syntax for all references to files to avoid ambiguity.

Example use case #

I'll use this example to illustrate how the builder works, but the injection mechanism is not limited to SASS files, as explained below. In this document, I'll refer to a package that is used as a dependency as dep, and to a package consuming dep and injecting assets into it as app.

I work on a package that contains Angular components, and a couple of web apps that use these components. Each app has a different design, so I need to set some CSS properties of the components from within the app packages. The component styles are compiled from SASS, so the most convenient solution (for a consumer of dep) would be if dep read these values from a file in app. I want that file to be app|lib/_variables.scss.

dep can't simply import a file from app, because SASS import paths must be statically known, and dep could be used by multiple apps. That's where this builder comes into play.

This package contains a builder inject_scss_files that looks for a provisional dep|lib/_variables.default.scss file and creates the final dep|lib/_variables.scss file. The contents of dep|lib/_variables.scss are copied from app|lib/_variables.scss, but the source file is configurable in the build configuration. This way, a package app2 could set app2|lib/_variables.scss as the source.

Now, components in dep can use the statically known import path dep|lib/_variables.scss, but will access the file contents from app at build time.

Injecting SASS files #

These are all the required steps to implement this use case. In dep, add this package to the dependencies. Also add a dependency on build_config to ensure compatibility with consumers of your package. Then, create a dep|build.yaml file with the following content:

  # When a package depending on `dep` is built, this build target is
  # automatically built too.
        enabled: true

In app|build.yaml, specify which assets should be injected for the .default assets:

        'dep|lib/_variables.default.scss': 'app|lib/_variables.scss'

If you don't specify a source for a .default asset, the asset itself will be used as the final file. This means that a consumer doesn't have to configure anything if they are satisfied with the default contents.

Side note on SASS files: app|lib/_variables.scss can import the default file with @import 'package:dep/variables.default';. Then, you only need to assign those variables you actually want to change.

Injecting assets with other extensions #

The Dart build system requires that builders statically declare all the file extensions they run on. This makes it impossible to process all .default.* files in a single builder. If you need to inject assets that don't end in .scss or .sass, you need to declare your own builder. You can use inject_asset_builder|build.yaml as a template; you should only need to change the build_extensions and file_extensions configuration and the builder name. Then reference it with $yourPackage|$builderName in builders and global_options.

pub points

A builder that makes it possible for a package to access files from packages depending on it.

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build, build_config, meta


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