refactor(@angular/build): support external runtime component stylesheets in application builder #28330
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…ets in application builder To support automatic component style HMR, `application` builder in development mode now provides support for generating external runtime component stylesheets. This capability leverages the upcoming support within the AOT -compiler to emit components that generate `link` elements instead of embedding the stylesheet contents for file-based styles (e.g., `styleUrl`). In combination with support within the development server to handle requests for component stylesheets, file-based component stylesheets will be able to be replaced without a full page reload. The implementation leverages the AOT compiler option `externalRuntimeStyles` which uses the result of the resource handler's resolution and emits new external stylesheet metadata within the component output code. This new metadata works in concert with the Angular runtime to generate `link` elements which can then leverage existing global stylesheet HMR capabilities. This capability is current disabled by default while all elements are integrated across the CLI and framework and can be controlled via the `NG_HMR_CSTYLES=1` environment variable. Once fully integrated the environment variable will unneeded. This feature is only intended for use with the development server. Component styles within in built code including production are not affected by this feature. NOTE: Rebuild times have not yet been optimized. Future improvements will reduce the component stylesheet only rebuild time case.
…component styles The build system will now transform inline styles into a corresponding external runtime style with a URL for the Angular AOT compiler when the development server has enabled component HMR for styles. This allows both file-based and inline component styles to be eligible for component style HMR. The inline styles are provided to the development server in an equivalent form to the file-based styles which the Angular runtime will request via `link` elements during development. A unique identifier is produced for each inline style that combines the containing file and order of the style within the containing file to represent the location of the style. This provides an equivalent unique identifier to the full path used by file-based styles.
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To support automatic component style HMR,
applicationbuilder in development mode now provides support for generating external runtime component stylesheets. This capability leverages the upcoming support within the AOT -compiler to emit components that generatelinkelements instead of embedding the stylesheet contents for file-based styles (e.g.,styleUrl). In combination with support within the development server to handle requests for component stylesheets, file-based component stylesheets will be able to be replaced without a full page reload.The implementation leverages the AOT compiler option
externalRuntimeStyleswhich uses the result of the resource handler's resolution and emits new external stylesheet metadata within the component output code. This new metadata works in concert with the Angular runtime to generatelinkelements which can then leverage existing global stylesheet HMR capabilities.This capability is current disabled by default while all elements are integrated across the CLI and framework and can be controlled via the
NG_HMR_CSTYLES=1environment variable. Once fully integrated the environment variable will unneeded.This feature is only intended for use with the development server. Component styles within built code including production are not affected by this feature.
NOTE: Rebuild times have not yet been optimized. Future improvements will reduce the component stylesheet only rebuild time case.