Task to infer static variables

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 1d9850e0ebab908e248cdb9fa0551867cc06dfbd..2a0815c95129c49f673bd02319741249d6c2a5ee 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -14,6 +14,7 @@ import 'package:analyzer/src/generated/engine.dart'
     hide AnalysisCache, AnalysisTask;
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/error_verifier.dart';
+import 'package:analyzer/src/generated/incremental_resolver.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/parser.dart';
 import 'package:analyzer/src/generated/resolver.dart';
@@ -185,6 +186,14 @@ final ListResultDescriptor<VariableElement> INFERABLE_STATIC_VARIABLES_IN_UNIT =
         'INFERABLE_STATIC_VARIABLES_IN_UNIT', null);
 
 /**
+ * An inferrable static variable ([VariableElement]) whose type has been
+ * inferred.
+ */
+final ResultDescriptor<VariableElement> INFERRED_STATIC_VARIABLE =
+    new ResultDescriptor<VariableElement>('INFERRED_STATIC_VARIABLE', null,
+        cachingPolicy: ELEMENT_CACHING_POLICY);
+
+/**
  * The partial [LibraryElement] associated with a library.
  *
  * The [LibraryElement] and its [CompilationUnitElement]s are attached to each
@@ -1673,7 +1682,7 @@ class ComputeInferableStaticVariableDependenciesTask
     //
     // Record outputs.
     //
-    outputs[INFERABLE_STATIC_VARIABLE_DEPENDENCIES] = gatherer.results;
+    outputs[INFERABLE_STATIC_VARIABLE_DEPENDENCIES] = gatherer.results.toList();
   }
 
   /**
@@ -2401,6 +2410,227 @@ class GenerateHintsTask extends SourceBasedAnalysisTask {
 }
 
 /**
+ * An abstract class that defines utility methods that are useful for tasks
+ * operating on static variables.
+ */
+abstract class InferStaticVariableTask extends ConstantEvaluationAnalysisTask {
+  InferStaticVariableTask(
+      InternalAnalysisContext context, VariableElement variable)
+      : super(context, variable);
+
+  /**
+   * Return the declaration of the target within the given compilation [unit].
+   * Throw an exception if the declaration cannot be found.
+   */
+  VariableDeclaration getDeclaration(CompilationUnit unit) {
+    VariableElement variable = target;
+    NodeLocator locator = new NodeLocator(variable.nameOffset);
+    AstNode node = locator.searchWithin(unit);
+    VariableDeclaration declaration =
+        node.getAncestor((AstNode ancestor) => ancestor is VariableDeclaration);
+    if (declaration == null || declaration.name != node) {
+      throw new AnalysisException(
+          "Failed to find the declaration of the variable ${variable.displayName} in ${variable.source}");
+    }
+    return declaration;
+  }
+}
+
+/**
+ * A task that ensures that all of the inferrable static variables in a
+ * compilation unit have had their type inferred.
+ */
+class InferStaticVariableTypesInUnitTask extends SourceBasedAnalysisTask {

[Paul Berry, 2015/08/29 01:14:55]

Since this task has dependencies which are other static variable types, it might
result in a circularity.  So this task needs to contain:

  @override
  bool get handlesDependencyCycles => true;

and its implementation of internalPerform() needs to check for a non-null value
of dependencyCycle.

Unlike in ComputeConstantValueTask, which can simply generate an error for
dependency cycles, I believe we need to have well-defined semantics for
dependency cycles.  IIRC, the way we decided to handle this was: infer the type
of each variable in the cycle assuming the other variables in the cycle have
type "dynamic", and then assign the types of all the variables in one go.

[Brian Wilkerson, 2015/08/31 15:08:52]

Sorry, I should have included this in a comment, but I'm aware of the need to
handle circularities and plan on doing so in a follow-on CL.

[Paul Berry, 2015/08/31 15:50:59]

Acknowledged.

+  /**
+   * The name of the input whose value is the [RESOLVED_UNIT5] for the
+   * compilation unit.
+   */
+  static const String UNIT_INPUT = 'UNIT_INPUT';
+
+  /**
+   * The name of the input whose value is a list of the inferrable static
+   * variables whose types have been computed.
+   */
+  static const String INFERRED_VARIABLES_INPUT = 'INFERRED_VARIABLES_INPUT';
+
+  /**
+   * The task descriptor describing this kind of task.
+   */
+  static final TaskDescriptor DESCRIPTOR = new TaskDescriptor(
+      'InferStaticVariableTypesInUnitTask',
+      createTask,
+      buildInputs,
+      <ResultDescriptor>[RESOLVED_UNIT6]);
+
+  /**
+   * Initialize a newly created task to build a library element for the given
+   * [unit] in the given [context].
+   */
+  InferStaticVariableTypesInUnitTask(
+      InternalAnalysisContext context, LibrarySpecificUnit unit)
+      : super(context, unit);
+
+  @override
+  TaskDescriptor get descriptor => DESCRIPTOR;
+
+  @override
+  void internalPerform() {
+    //
+    // Prepare inputs.
+    //
+    CompilationUnit unit = getRequiredInput(UNIT_INPUT);
+    //
+    // Record outputs. There is no additional work to be done at this time
+    // because the work has implicitly been done by virtue of the task model
+    // preparing all of the inputs.
+    //
+    outputs[RESOLVED_UNIT6] = unit;
+  }
+
+  /**
+   * Return a map from the names of the inputs of this kind of task to the task
+   * input descriptors describing those inputs for a task with the given
+   * [libSource].
+   */
+  static Map<String, TaskInput> buildInputs(AnalysisTarget target) {
+    LibrarySpecificUnit unit = target;
+    return <String, TaskInput>{
+      INFERRED_VARIABLES_INPUT: INFERABLE_STATIC_VARIABLES_IN_UNIT
+          .of(unit)
+          .toListOf(INFERRED_STATIC_VARIABLE),
+      UNIT_INPUT: RESOLVED_UNIT5.of(unit)
+    };
+  }
+
+  /**
+   * Create a [InferStaticVariableTypesInUnitTask] based on the given [target] in the
+   * given [context].
+   */
+  static InferStaticVariableTypesInUnitTask createTask(
+      AnalysisContext context, AnalysisTarget target) {
+    return new InferStaticVariableTypesInUnitTask(context, target);
+  }
+}
+
+/**
+ * A task that computes the type of an inferrable static variable and
+ * stores it in the element model.
+ */
+class InferStaticVariableTypeTask extends InferStaticVariableTask {
+  /**
+   * The name of the input which ensures that dependent values have their type
+   * inferred before the target.
+   */
+  static const String DEPENDENCIES_INPUT = 'DEPENDENCIES_INPUT';
+
+  /**
+   * The name of the [TYPE_PROVIDER] input.
+   */
+  static const String TYPE_PROVIDER_INPUT = 'TYPE_PROVIDER_INPUT';
+
+  /**
+   * The name of the [RESOLVED_UNIT5] input.
+   */
+  static const String UNIT_INPUT = 'UNIT_INPUT';
+
+  static final TaskDescriptor DESCRIPTOR = new TaskDescriptor(
+      'InferStaticVariableTypeTask',
+      createTask,
+      buildInputs,
+      <ResultDescriptor>[INFERRED_STATIC_VARIABLE]);
+
+  InferStaticVariableTypeTask(
+      InternalAnalysisContext context, VariableElement variable)
+      : super(context, variable);
+
+  @override
+  TaskDescriptor get descriptor => DESCRIPTOR;
+
+  @override
+  bool get handlesDependencyCycles => true;
+
+  @override
+  void internalPerform() {
+    //
+    // Prepare inputs.
+    //
+    // Note: DEPENDENCIES_INPUT is not needed.  It is merely a bookkeeping
+    // dependency to ensure that the variables that this variable references
+    // have types inferred before inferring the type of this variable.
+    //
+    VariableElementImpl variable = target;
+    CompilationUnit unit = getRequiredInput(UNIT_INPUT);
+    TypeProvider typeProvider = getRequiredInput(TYPE_PROVIDER_INPUT);
+    //
+    // Re-resolve the variable's initializer so that the inferred types of other
+    // variables will be propagated.
+    //
+    NodeLocator locator = new NodeLocator(variable.nameOffset);
+    AstNode node = locator.searchWithin(unit);
+    VariableDeclaration declaration =
+        node.getAncestor((AstNode ancestor) => ancestor is VariableDeclaration);
+    if (declaration == null || declaration.name != node) {
+      throw new AnalysisException(
+          "NodeLocator failed to find a variable's declaration");
+    }
+    RecordingErrorListener errorListener = new RecordingErrorListener();
+    Expression initializer = declaration.initializer;
+    ResolutionContext resolutionContext =
+        ResolutionContextBuilder.contextFor(initializer, errorListener);
+    ResolverVisitor visitor = new ResolverVisitor(
+        variable.library, variable.source, typeProvider, errorListener,
+        nameScope: resolutionContext.scope);
+    if (resolutionContext.enclosingClassDeclaration != null) {
+      visitor.prepareToResolveMembersInClass(
+          resolutionContext.enclosingClassDeclaration);
+    }
+    visitor.initForIncrementalResolution();

[Paul Berry, 2015/08/29 01:14:55]

It seems weird that we both manually initialize the visitor for incremental
resolution (by calling visitor.prepareToResolveMembersInClass()) and tell it to
initialize itself for incremental resolution.  As a future improvement, consider
making resolutionContext a parameter to initForIncrementalResolution() so that
the visitor takes care of all the initialization in one call.

[Brian Wilkerson, 2015/08/31 15:08:52]

The method initForIncrementalResolution() is also called from the incremental
resolver, and I didn't want to re-factor that code as part of this CL, so I left
it as it was. I certainly don't mind if someone wants to look for a cleaner way
to structure these methods at a later time.

+    initializer.accept(visitor);
+    //
+    // Record the type of the variable.
+    //
+    DartType newType = initializer.staticType;
+    variable.type = newType;
+    (variable.initializer as ExecutableElementImpl).returnType = newType;
+    if (variable is PropertyInducingElementImpl) {
+      setReturnType(variable.getter, newType);
+      setParameterType(variable.setter, newType);
+    }
+    //
+    // Record outputs.
+    //
+    outputs[INFERRED_STATIC_VARIABLE] = variable;
+  }
+
+  /**
+   * Return a map from the names of the inputs of this kind of task to the task
+   * input descriptors describing those inputs for a task with the given
+   * [target].
+   */
+  static Map<String, TaskInput> buildInputs(AnalysisTarget target) {
+    VariableElement variable = target;
+    LibrarySpecificUnit unit =
+        new LibrarySpecificUnit(variable.library.source, variable.source);
+    return <String, TaskInput>{
+      DEPENDENCIES_INPUT: INFERABLE_STATIC_VARIABLE_DEPENDENCIES
+          .of(variable)
+          .toListOf(INFERRED_STATIC_VARIABLE),
+      TYPE_PROVIDER_INPUT: TYPE_PROVIDER.of(AnalysisContextTarget.request),
+      UNIT_INPUT: RESOLVED_UNIT5.of(unit)
+    };
+  }
+
+  /**
+   * Create a [InferStaticVariableTypeTask] based on the given [target] in the
+   * given [context].
+   */
+  static InferStaticVariableTypeTask createTask(
+      AnalysisContext context, AnalysisTarget target) {
+    return new InferStaticVariableTypeTask(context, target);
+  }
+}
+
+/**
  * A task computes all of the errors of all of the units for a single
  * library source and sets the [LIBRARY_ERRORS_READY] flag.
  */