Fasta type inference prototype #2

pkg/front_end/lib/src/fasta/builder/shadow_ast.dart

Index: pkg/front_end/lib/src/fasta/builder/shadow_ast.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/shadow_ast.dart b/pkg/front_end/lib/src/fasta/builder/shadow_ast.dart
new file mode 100644
index 0000000000000000000000000000000000000000..2f064e4a34c313e8eb331dab345f412b74872262
--- /dev/null
+++ b/pkg/front_end/lib/src/fasta/builder/shadow_ast.dart
@@ -0,0 +1,195 @@
+import 'package:front_end/src/fasta/type_inference/local_type_inferrer.dart';
+import 'package:kernel/ast.dart' show DartType, InterfaceType;
+import 'package:kernel/core_types.dart';
+
+abstract class Block implements Statement {
+  Iterable<Statement> get shadowStatements;
+
+  @override
+  void shadowInfer(LocalTypeInferrer inferrer, FunctionContext context) {
+    for (var statement in shadowStatements) {
+      statement.shadowInfer(inferrer, context);
+    }
+  }
+}
+
+abstract class Expression {
+  DartType shadowInfer(
+      LocalTypeInferrer inferrer, DartType context, bool typeNeeded);
+}
+
+abstract class FunctionExpression implements Expression {
+  void set shadowInferredReturnType(DartType type);
+
+  Statement get shadowBody;
+
+  bool get shadowIsAsync;
+
+  bool get shadowIsExpressionFunction;
+
+  bool get shadowIsGenerator;
+
+  DartType shadowMakeFunctionType();
+
+  @override
+  DartType shadowInfer(
+      LocalTypeInferrer inferrer, DartType context, bool typeNeeded) {
+    // TODO(paulberry): infer argument types and type parameters.
+    // TODO(paulberry): full support for generators.
+    Statement body = shadowBody;
+    // TODO(paulberry): Dart 1.0 rules say we only need to set the function
+    // node's return type if it uses expression syntax.  Does that make sense
+    // for Dart 2.0?
+    bool needToSetReturnType = shadowIsExpressionFunction;
+    bool returnTypeNeeded = typeNeeded || needToSetReturnType;
+    bool isAsync = shadowIsAsync;
+    var functionContext = new FunctionContext(
+        inferrer, returnTypeNeeded, isAsync, shadowIsGenerator);
+    body.shadowInfer(inferrer, functionContext);
+    DartType inferredReturnType;
+    if (needToSetReturnType || typeNeeded) {
+      inferredReturnType = functionContext.inferredReturnType;
+      if (isAsync) {
+        inferredReturnType = new InterfaceType(
+            inferrer.coreTypes.futureClass, <DartType>[inferredReturnType]);
+      }
+    }
+    if (needToSetReturnType) {
+      this.shadowInferredReturnType = inferredReturnType;
+    }
+    if (typeNeeded) {
+      return shadowMakeFunctionType();
+    } else {
+      return null;
+    }
+  }
+}
+
+abstract class IntLiteral implements Expression {
+  @override
+  DartType shadowInfer(
+      LocalTypeInferrer inferrer, DartType context, bool typeNeeded) {
+    return typeNeeded ? inferrer.coreTypes.intClass.rawType : null;
+  }
+}
+
+abstract class ListLiteral implements Expression {
+  DartType get declaredTypeArgumentForInference;
+
+  Iterable<Expression> get expressionsForInference;
+
+  void set inferredTypeArgument(DartType type);
+
+  @override
+  DartType shadowInfer(
+      LocalTypeInferrer inferrer, DartType context, bool typeNeeded) {
+    DartType declaredTypeArgument = declaredTypeArgumentForInference;
+    DartType typeArgumentContext = declaredTypeArgument;
+    if (typeArgumentContext == null) {
+      if (context is InterfaceType &&
+          context.classNode == inferrer.coreTypes.listClass &&
+          context.typeArguments.length == 1) {
+        typeArgumentContext = context.typeArguments[0];
+      } else if (context != null) {
+        // TODO(paulberry): report an error?
+        throw new UnimplementedError('$context');

[scheglov, 2017/03/24 15:38:10]

If I understand correctly, "context" will be Iterable<String> here.

main() {
  foo(['aaa', 'bbb']);
}
foo(Iterable<String> p) {}

[Paul Berry, 2017/03/24 17:59:50]

You are correct.  This entire method is a hack that I put in place just to get
some simple cases prototyped, and I don't intend to ever land this code.  The
right way to do this is to do something like StaticTypeAnalyzer.inferListType
(pkg/analyzer/lib/src/generated/static_type_analyzer.dart), which sets up the
proper preconditions and then calls inferGenericFunctionOrType, which handles
the "Iterable" case as part of its general-purpose algorithm.

+      }
+    }
+    DartType inferredTypeArgument = typeArgumentContext;
+    bool typeArgumentNeeded = inferredTypeArgument == null;
+    for (Expression e in expressionsForInference) {
+      DartType t =
+          e.shadowInfer(inferrer, typeArgumentContext, typeArgumentNeeded);
+      if (typeArgumentNeeded) {
+        inferredTypeArgument = inferrer.union(inferredTypeArgument, t);
+      }
+    }
+    if (inferredTypeArgument == null) {
+      // Empty list.
+      throw new UnimplementedError();
+    }
+    if (declaredTypeArgument == null) {
+      this.inferredTypeArgument = inferredTypeArgument;
+    }
+    if (typeNeeded) {
+      return new InterfaceType(
+          inferrer.coreTypes.listClass, <DartType>[inferredTypeArgument]);
+    } else {
+      return null;
+    }
+  }
+}
+
+abstract class NullLiteral implements Expression {
+  @override
+  DartType shadowInfer(
+      LocalTypeInferrer inferrer, DartType context, bool typeNeeded) {
+    return typeNeeded ? inferrer.coreTypes.nullClass.rawType : null;
+  }
+}
+
+abstract class ReturnStatement implements Statement {
+  Expression get expressionForInference;
+
+  @override
+  void shadowInfer(LocalTypeInferrer inferrer, FunctionContext context) {
+    DartType expressionContext = null; // TODO(paulberry): probably wrong.
+    bool expressionTypeNeeded =
+        context.returnTypeNeeded && !context.isGenerator;
+    DartType expressionType = expressionForInference.shadowInfer(
+        inferrer, expressionContext, expressionTypeNeeded);
+    if (expressionTypeNeeded) {
+      if (context.isAsync) {
+        expressionType = _unwrapFuture(inferrer.coreTypes, expressionType);
+      }
+      context.recordReturnType(expressionType);
+    }
+  }
+
+  DartType _unwrapFuture(CoreTypes coreTypes, DartType type) {
+    // TODO(paulberry): replace with a full implementation of what's in the spec
+    // (e.g. handle types derived from Future).  Also probably move to Kernel.
+    if (type is InterfaceType && type.classNode == coreTypes.futureClass) {
+      return type.typeArguments[0];
+    } else {
+      return type;
+    }
+  }
+}
+
+abstract class Statement {
+  void shadowInfer(LocalTypeInferrer inferrer, FunctionContext context);
+}
+
+abstract class VariableDeclaration implements Statement {
+  DartType get shadowDeclaredType;
+
+  DartType get shadowInferredType;
+
+  void set shadowInferredType(DartType type);
+
+  Expression get shadowInitializer;
+
+  @override
+  void shadowInfer(LocalTypeInferrer inferrer, FunctionContext context) {
+    Expression initializer = shadowInitializer;
+    if (initializer != null) {
+      DartType type = shadowDeclaredType;
+      DartType inferredType =
+          initializer.shadowInfer(inferrer, type, type == null);
+      if (type == null) {
+        this.shadowInferredType = inferredType;
+      }
+    }
+  }
+}
+
+abstract class VariableGet implements Expression {
+  VariableDeclaration get shadowDeclaration;
+
+  @override
+  DartType shadowInfer(
+      LocalTypeInferrer inferrer, DartType context, bool typeNeeded) {
+    return typeNeeded ? shadowDeclaration.shadowInferredType : null;
+  }
+}