async 2.0.0.AssetNode.whenAvailable to be a generic method to fix a new strong mode error.CancelableFuture to match the new Future.then type signature. The onValue parameter now has a return type of FutureOr<S> instead of S.$dart2js).StaticPackageProvider class to more efficiently handle immutable, untransformed packages.collection package.source_maps' Span class to source_span's SourceSpan class.pool package.Add an AggregateTransformer type. Aggregate transformers transform groups of assets for which no single asset is primary. For example, one could be used to merge all images in a directory into a single file.
Add a message getter to TransformerException and AssetLoadException.
Fix a bug where transformers would occasionally emit stale output after their inputs changed.
PackageProvider.getAsset().Breaking change: when an output of a lazy transformer is requested, that transformer will run long enough to generate the output, then become lazy again. Previously, it would become eager as soon as an asset had been requested.
Only run Transformer.isPrimary and Transformer.declareOutputs once for each asset.
Lazy transformers' laziness is preserved when followed by declaring transformers, or by normal transformers for which the lazy outputs aren't primary.
Fix a bug where reading the primary input using Transform.readInputAsString had slightly different behavior than reading it using Transform.primary.readAsString.
Fix a crashing bug when Barback.getAllAssets is called synchronously after creating a new Barback instance.
Don‘t warn if a lazy or declaring transformer doesn’t emit outputs that it has declared. This is valid for transformers like dart2js that need to read their primary input in order to determine whether they should run.
Allow Transformer.isPrimary, Transformer.apply, and DeclaringTransformer.declareOutputs to return non-Future values if they run synchronously.
Fix a deadlock bug when a lazy primary input to a lazy transformer became dirty while the transformer's apply method was running.
Run declaring transformers with lazy inputs eagerly if the inputs become available.
Transformer.isPrimary now takes an AssetId rather than an Asset.
DeclaringTransform now only exposes the primary input's AssetId, rather than the primary Asset object.
DeclaringTransform no longer supports getInput, readInput, readInputAsString, or hasInput.
Add a Transform.logger.fine function that doesn't print its messages by default. When using Barback with pub in verbose mode, these messages will be printed.
Add a Transform.hasInput function that returns whether or not a given secondary input exists.
Transformer.allowedExtensions now supports extensions containing multiple periods, such as .dart.js.
Transforms now pass their primary inputs through to the next phase by default. A transformer may still overwrite its primary input without causing a collision. If a transformer doesn't overwrite its primary input, it may cause it not to be passed through by calling Transform.consumePrimary. The primary input will be consumed by default if a transformer throws an error.
If an input requested with Transform.getInput, Transform.readInput, or Transform.readInputAsString cannot be found, an AssetNotFoundException will be thrown. This was always what the documentation said, but previously a MissingInputException was thrown instead.
If a transformer calls Transform.logger.error, the transformer will now be considered to have failed after it finishes running apply(). This means that its outputs will not be consumed by future transformers and its primary input will not be passed through to the next phase.
If a transform calls Transform.getInput, Transform.readInput, Transform.readInputAsString, or Transform.hasInput on an input that doesn't exist, the transform will be re-run if that input is created in the future.