Check if we can read assets before asking for their digests (#3566)

build_resolvers/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 2.3.1
+
+- Fix a bug in the transitive digest builder, ensure we check if assets are
+ readable before asking for their digest.
+
 ## 2.3.0
 
 - Improve performance for resolves by adding a builder which serializes

build_resolvers/lib/builder.dart

@@ -37,11 +37,8 @@ class _TransitiveDigestsBuilder extends Builder {
  continue;
  }
 
- // Otherwise, add its digest and queue all its dependencies to crawl.
- byteSink.add((await buildStep.digest(next)).bytes);
- final deps = await dependenciesOf(next, buildStep);
- if (deps == null) {
- // We warn here but do not fail, the downside is slower builds.
+ // We warn here but do not fail, the downside is slower builds.
+ if (!(await buildStep.canRead(next))) {
  log.warning('''
 Unable to read asset, could not compute transitive deps: $next
 
@@ -50,6 +47,12 @@ https://github.com/dart-lang/build/blob/master/docs/faq.md#unable-to-read-asset-
  return;
  }
 
+ // Otherwise, add its digest and queue all its dependencies to crawl.
+ byteSink.add((await buildStep.digest(next)).bytes);
+
+ // We know this isn't null since we already checked if we can read `next`.
+ final deps = (await dependenciesOf(next, buildStep))!;
+
  // Add all previously unseen deps to the queue.
  for (final dep in deps) {
  if (seen.add(dep)) queue.add(dep);

build_resolvers/pubspec.yaml

@@ -1,5 +1,5 @@
 name: build_resolvers
-version: 2.3.0
+version: 2.3.1
 description: Resolve Dart code in a Builder
 repository: https://github.com/dart-lang/build/tree/master/build_resolvers