Removes unused feature target.dependencies and ciYaml.getInitialTargets(). (#4713)

Note that `target.properties.dependencies`, something entirely different, is not affected.

Closes flutter/flutter#169103.

Author: matanlurey

app_dart/lib/src/model/ci_yaml/ci_yaml.dart

@@ -100,16 +100,6 @@ final class CiYamlSet {
   List<String>? totPostsubmitTargetNames({CiType type = CiType.any}) =>
       configs[type]!.totPostsubmitTargetNames;
 
-  /// Filters [targets] to those that should be started immediately.
-  ///
-  /// Targets with a dependency are triggered when there dependency pushes a notification that it has finished.
-  /// This shouldn't be confused for targets that have the property named dependency, which is used by the
-  /// flutter_deps recipe module on LUCI.
-  List<Target> getInitialTargets(
-    List<Target> targets, {
-    CiType type = CiType.any,
-  }) => configs[type]!.getInitialTargets(targets);
-
   /// Get an unfiltered list of all [targets] that are found in the ci.yaml file.
   List<Target> targets({CiType type = CiType.any}) => configs[type]!.targets;
 }
@@ -284,24 +274,6 @@ class CiYaml {
     }).toList();
   }
 
-  /// Filters [targets] to those that should be started immediately.
-  ///
-  /// Targets with a dependency are triggered when there dependency pushes a notification that it has finished.
-  /// This shouldn't be confused for targets that have the property named dependency, which is used by the
-  /// flutter_deps recipe module on LUCI.
-  List<Target> getInitialTargets(List<Target> targets) {
-    Iterable<Target> initialTargets =
-        targets.where((Target target) => target.dependencies.isEmpty).toList();
-    if (branch != Config.defaultBranch(slug)) {
-      // Filter out bringup targets for release branches
-      initialTargets = initialTargets.where(
-        (Target target) => !target.isBringup,
-      );
-    }
-
-    return initialTargets.toList();
-  }
-
   Iterable<Target> get _targets => config.targets.map(
     (pb.Target target) =>
         Target(schedulerConfig: config, value: target, slug: slug),
@@ -420,24 +392,6 @@ class CiYaml {
           continue;
         }
         targetGraph[target.name] = <pb.Target>[];
-        // Add edges
-        if (target.dependencies.isNotEmpty) {
-          if (target.dependencies.length != 1) {
-            exceptions.add(
-              'ERROR: ${target.name} has multiple dependencies which is not supported. Use only one dependency',
-            );
-          } else {
-            if (target.dependencies.first == target.name) {
-              exceptions.add('ERROR: ${target.name} cannot depend on itself');
-            } else if (targetGraph.containsKey(target.dependencies.first)) {
-              targetGraph[target.dependencies.first]!.add(target);
-            } else {
-              exceptions.add(
-                'ERROR: ${target.name} depends on ${target.dependencies.first} which does not exist',
-              );
-            }
-          }
-        }
 
         // To add or change validations that are specific to a repository, such as flutter/flutter,
         // see https://github.com/flutter/flutter/blob/master/dev/bots/test/ci_yaml_validation_test.dart.

app_dart/lib/src/model/ci_yaml/target.dart

@@ -143,11 +143,6 @@ final class Target {
     _value.enabledBranches,
   );
 
-  /// The target's dependencies.
-  ///
-  /// This list is unmodifiable.
-  late final List<String> dependencies = List.unmodifiable(_value.dependencies);
-
   /// The target's `runIf` configuration.
   ///
   /// This list is unmodifiable.

app_dart/lib/src/model/proto/internal/scheduler.pb.dart

@@ -32,7 +32,7 @@ message Target {
     // Unique, human readable identifier.
     optional string name = 1;
     // Names of other targets required to succeed before triggering this target.
-    repeated string dependencies = 2;
+    reserved 2; // dependencies
     // Whether this target is stable and can be used to gate commits.
     // Defaults to false which blocks builds and does not run in presubmit.
     optional bool bringup = 3 [default = false];

app_dart/lib/src/model/proto/internal/scheduler.pbjson.dart

@@ -162,17 +162,13 @@ class Scheduler {
       commit.toRef(),
       postsubmit: true,
     );
-    final targets = ciYaml.getInitialTargets(ciYaml.postsubmitTargets());
+    final targets = ciYaml.postsubmitTargets();
     final isFusion = commit.slug == Config.flutterSlug;
     if (isFusion) {
       final fusionPostTargets = ciYaml.postsubmitTargets(
         type: CiType.fusionEngine,
       );
-      final fusionInitialTargets = ciYaml.getInitialTargets(
-        fusionPostTargets,
-        type: CiType.fusionEngine,
-      );
-      targets.addAll(fusionInitialTargets);
+      targets.addAll(fusionPostTargets);
       // Note on post submit targets: CiYaml filters out release_true for release branches and fusion trees
     }