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added hasInput funtion to Reader/BuildStep #17

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added hasInput funtion to Reader/BuildStep #17

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2 changes: 2 additions & 0 deletions lib/src/asset/reader.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -8,4 +8,6 @@ import 'id.dart';

abstract class AssetReader {
Future<String> readAsString(AssetId id, {Encoding encoding: UTF8});

Future<bool> hasInput(AssetId id);
}
6 changes: 6 additions & 0 deletions lib/src/builder/build_step.dart
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Expand Up @@ -13,6 +13,12 @@ abstract class BuildStep {
/// The primary input for this build step.
Asset get input;

/// Checks if an [Asset] by [id] exists as an input for this [BuildStep].
///
/// If [trackAsDependency] is true, then [id] will be marked as a dependency
/// of all [expectedOutputs].
Future<bool> hasInput(AssetId id, {bool trackAsDependency: true});
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Is trackAsDependency something we want to expose to users, or should it be an implementation detail?

I feel like you had a use case for it, but I can't remember what it is right now.

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What does it mean if the user passes false for this? Presumable, the caller uses the boolean result of this method to do something that affects their build output. If that boolean were to change without the build step being re-run (because it passed trackAsDependency: false), won't you end up with stale or inconsistent output?

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After some offline discussions I am going to remove this as part of the public api, at least for now, as well as removing the addDependency function. These combined would allow you to write a builder that cheats a bit in terms of marking its dependencies, which specifically when doing resolution would be useful. We may consider adding it back in the future, but for now it doesn't need to be there.

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I will do that in a followup cl though


/// Reads an [Asset] by [id] as a [String] using [encoding].
///
/// If [trackAsDependency] is true, then [id] will be marked as a dependency
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9 changes: 9 additions & 0 deletions lib/src/builder/build_step_impl.dart
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Expand Up @@ -49,6 +49,15 @@ class BuildStepImpl implements BuildStep {
_dependencies.add(input.id);
}

/// Checks if an [Asset] by [id] exists as an input for this [BuildStep].
///
/// If [trackAsDependency] is true, then [id] will be marked as a dependency
/// of all [expectedOutputs].
Future<bool> hasInput(AssetId id, {bool trackAsDependency: true}) {
if (trackAsDependency) _dependencies.add(id);
return _reader.hasInput(id);
}

/// Reads an [Asset] by [id] as a [String] using [encoding].
///
/// If [trackAsDependency] is true, then [id] will be marked as a dependency
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6 changes: 6 additions & 0 deletions lib/src/generate/build.dart
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Expand Up @@ -122,6 +122,12 @@ Stream<Asset> _runBuilder(Builder builder, List<AssetId> inputs) async* {
class _SimpleAssetReader implements AssetReader {
const _SimpleAssetReader();

@override
Future<bool> hasInput(AssetId id) async {
assert(id.package == _localPackageName);
return new File(id.path).exists();
}

@override
Future<String> readAsString(AssetId id, {Encoding encoding: UTF8}) async {
assert(id.package == _localPackageName);
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4 changes: 4 additions & 0 deletions lib/src/transformer/transformer.dart
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Expand Up @@ -89,6 +89,10 @@ class _TransformAssetReader implements AssetReader {

_TransformAssetReader(this.transform);

@override
Future<bool> hasInput(build.AssetId id) =>
transform.hasInput(_toBarbackAssetId(id));

@override
Future<String> readAsString(build.AssetId id, {Encoding encoding: UTF8}) =>
transform.readInputAsString(_toBarbackAssetId(id), encoding: encoding);
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20 changes: 20 additions & 0 deletions test/builder/build_step_impl_test.dart
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Expand Up @@ -35,6 +35,26 @@ main() {
var a2 = makeAssetId();
await buildStep.readAsString(a2);
expect(buildStep.dependencies, [primary.id, a1, a2]);

var a3 = makeAssetId();
await buildStep.readAsString(a3, trackAsDependency: false);
expect(buildStep.dependencies.contains(a3), isFalse);
});

test('tracks dependencies on hasInput', () async {
expect(buildStep.dependencies, [primary.id]);

var a1 = makeAssetId();
await buildStep.hasInput(a1);
expect(buildStep.dependencies, [primary.id, a1]);

var a2 = makeAssetId();
await buildStep.hasInput(a2);
expect(buildStep.dependencies, [primary.id, a1, a2]);

var a3 = makeAssetId();
await buildStep.hasInput(a3, trackAsDependency: false);
expect(buildStep.dependencies.contains(a3), isFalse);
});

test('addDependency adds dependencies', () {
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6 changes: 5 additions & 1 deletion test/common/in_memory_reader.dart
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Expand Up @@ -11,8 +11,12 @@ class InMemoryAssetReader implements AssetReader {

InMemoryAssetReader(this.assets);

Future<bool> hasInput(AssetId id) {
return new Future.value(assets.containsKey(id));
}

Future<String> readAsString(AssetId id, {Encoding encoding: UTF8}) async {
if (!assets.containsKey(id)) throw new AssetNotFoundException(id);
if (!await hasInput(id)) throw new AssetNotFoundException(id);
return assets[id];
}
}
2 changes: 2 additions & 0 deletions test/common/stub_reader.dart
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Expand Up @@ -7,6 +7,8 @@ import 'dart:convert';
import 'package:build/build.dart';

class StubAssetReader implements AssetReader {
Future<bool> hasInput(AssetId id) => new Future.value(null);

Future<String> readAsString(AssetId id, {Encoding encoding: UTF8}) =>
new Future.value(null);
}