sdk/pkg/kernel/lib/target/targets.dart

// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library kernel.target.targets;

import '../ast.dart';
import '../class_hierarchy.dart';
import '../core_types.dart';
import '../reference_from_index.dart';
import 'changed_structure_notifier.dart';

final List<String> targetNames = targets.keys.toList();

class TargetFlags {
  final bool trackWidgetCreation;
  final int forceLateLoweringsForTesting;
  final bool forceLateLoweringSentinelForTesting;
  final bool forceStaticFieldLoweringForTesting;
  final bool forceNoExplicitGetterCallsForTesting;
  final bool enableNullSafety;

  const TargetFlags(
      {this.trackWidgetCreation = false,
      this.forceLateLoweringsForTesting = LateLowering.none,
      this.forceLateLoweringSentinelForTesting = false,
      this.forceStaticFieldLoweringForTesting = false,
      this.forceNoExplicitGetterCallsForTesting = false,
      this.enableNullSafety = false});

  bool operator ==(other) {
    if (identical(this, other)) return true;
    return other is TargetFlags &&
        trackWidgetCreation == other.trackWidgetCreation &&
        forceLateLoweringsForTesting == other.forceLateLoweringsForTesting &&
        forceLateLoweringSentinelForTesting ==
            other.forceLateLoweringSentinelForTesting &&
        forceStaticFieldLoweringForTesting ==
            other.forceStaticFieldLoweringForTesting &&
        forceNoExplicitGetterCallsForTesting ==
            other.forceNoExplicitGetterCallsForTesting &&
        enableNullSafety == other.enableNullSafety;
  }

  int get hashCode {
    int hash = 485786;
    hash = 0x3fffffff & (hash * 31 + (hash ^ trackWidgetCreation.hashCode));
    hash = 0x3fffffff &
        (hash * 31 + (hash ^ forceLateLoweringsForTesting.hashCode));
    hash = 0x3fffffff &
        (hash * 31 + (hash ^ forceLateLoweringSentinelForTesting.hashCode));
    hash = 0x3fffffff &
        (hash * 31 + (hash ^ forceStaticFieldLoweringForTesting.hashCode));
    hash = 0x3fffffff &
        (hash * 31 + (hash ^ forceNoExplicitGetterCallsForTesting.hashCode));
    hash = 0x3fffffff & (hash * 31 + (hash ^ enableNullSafety.hashCode));
    return hash;
  }
}

typedef Target _TargetBuilder(TargetFlags flags);

final Map<String, _TargetBuilder> targets = <String, _TargetBuilder>{
  'none': (TargetFlags flags) => new NoneTarget(flags),
};

Target? getTarget(String name, TargetFlags flags) {
  _TargetBuilder? builder = targets[name];
  if (builder == null) return null;
  return builder(flags);
}

abstract class DiagnosticReporter<M, C> {
  void report(M message, int charOffset, int length, Uri fileUri,
      {List<C> context});
}

/// The different kinds of number semantics supported by the constant evaluator.
enum NumberSemantics {
  /// Dart VM number semantics.
  vm,

  /// JavaScript (Dart2js and DDC) number semantics.
  js,
}

// Backend specific constant evaluation behavior
class ConstantsBackend {
  const ConstantsBackend();

  /// Lowering of a list constant to a backend-specific representation.
  Constant lowerListConstant(ListConstant constant) => constant;

  /// Returns `true` if [constant] is lowered list constant created by
  /// [lowerListConstant].
  bool isLoweredListConstant(Constant constant) => false;

  /// Calls `f` for each element in the lowered list [constant].
  ///
  /// This assumes that `isLoweredListConstant(constant)` is true.
  void forEachLoweredListConstantElement(
      Constant constant, void Function(Constant element) f) {}

  /// Lowering of a set constant to a backend-specific representation.
  Constant lowerSetConstant(SetConstant constant) => constant;

  /// Returns `true` if [constant] is lowered set constant created by
  /// [lowerSetConstant].
  bool isLoweredSetConstant(Constant constant) => false;

  /// Calls `f` for each element in the lowered set [constant].
  ///
  /// This assumes that `isLoweredSetConstant(constant)` is true.
  void forEachLoweredSetConstantElement(
      Constant constant, void Function(Constant element) f) {}

  /// Lowering of a map constant to a backend-specific representation.
  Constant lowerMapConstant(MapConstant constant) => constant;

  /// Returns `true` if [constant] is lowered map constant created by
  /// [lowerMapConstant].
  bool isLoweredMapConstant(Constant constant) => false;

  /// Calls `f` for each key/value pair in the lowered map [constant].
  ///
  /// This assumes that `lowerMapConstant(constant)` is true.
  void forEachLoweredMapConstantEntry(
      Constant constant, void Function(Constant key, Constant value) f) {}

  /// Number semantics to use for this backend.
  NumberSemantics get numberSemantics => NumberSemantics.vm;

  /// Inline control of constant variables. The given constant expression
  /// is the initializer of a [Field] or [VariableDeclaration] node.
  /// If this method returns `true`, the variable will be inlined at all
  /// points of reference and the variable itself removed (unless overridden
  /// by the `keepFields` or `keepLocals` properties).
  /// This method must be deterministic, i.e. it must always return the same
  /// value for the same constant value and place in the AST.
  bool shouldInlineConstant(ConstantExpression initializer) => true;

  /// Whether this target supports unevaluated constants.
  ///
  /// If not, then trying to perform constant evaluation without an environment
  /// raises an exception.
  ///
  /// This defaults to `false` since it requires additional work for a backend
  /// to support unevaluated constants.
  bool get supportsUnevaluatedConstants => false;

  /// If `true` constant [Field] declarations are not removed from the AST even
  /// when use-sites are inlined.
  ///
  /// All use-sites will be rewritten based on [shouldInlineConstant].
  bool get keepFields => true;

  /// If `true` constant [VariableDeclaration]s are not removed from the AST
  /// even when use-sites are inlined.
  ///
  /// All use-sites will be rewritten based on [shouldInlineConstant].
  bool get keepLocals => false;
}

/// A target provides backend-specific options for generating kernel IR.
abstract class Target {
  TargetFlags get flags;
  String get name;

  /// A list of URIs of required libraries, not including dart:core.
  ///
  /// Libraries will be loaded in order.
  List<String> get extraRequiredLibraries => const <String>[];

  /// A list of URIs of extra required libraries when compiling the platform.
  ///
  /// Libraries will be loaded in order after the [extraRequiredLibraries]
  /// above.
  ///
  /// Normally not needed, but can be useful if removing libraries from the
  /// [extraRequiredLibraries] list so libraries will still be available in the
  /// platform if having a weird mix of current and not-quite-current as can
  /// sometimes be the case.
  List<String> get extraRequiredLibrariesPlatform => const <String>[];

  /// A list of URIs of libraries to be indexed in the CoreTypes index, not
  /// including dart:_internal, dart:async, dart:core and dart:mirrors.
  List<String> get extraIndexedLibraries => const <String>[];

  /// Additional declared variables implied by this target.
  ///
  /// These can also be passed on the command-line of form `-D<name>=<value>`,
  /// and those provided on the command-line take precedence over those defined
  /// by the target.
  Map<String, String> get extraDeclaredVariables => const <String, String>{};

  /// Classes from the SDK whose interface is required for the modular
  /// transformations.
  Map<String, List<String>> get requiredSdkClasses => CoreTypes.requiredClasses;

  /// A derived class may change this to `true` to enable forwarders to
  /// user-defined `noSuchMethod` that are generated for each abstract member
  /// if such `noSuchMethod` is present.
  ///
  /// The forwarders are abstract [Procedure]s with [isNoSuchMethodForwarder]
  /// bit set.  The implementation of the behavior of such forwarders is up
  /// for the target backend.
  bool get enableNoSuchMethodForwarders => false;

  /// A derived class may change this to `true` to enable Flutter specific
  /// "super-mixins" semantics.
  ///
  /// This semantics relaxes a number of constraint previously imposed on
  /// mixins. Importantly it imposes the following change:
  ///
  ///     An abstract class may contain a member with a super-invocation that
  ///     corresponds to a member of the superclass interface, but where the
  ///     actual superclass does not declare or inherit a matching method.
  ///     Since no amount of overriding can change this property, such a class
  ///     cannot be extended to a class that is not abstract, it can only be
  ///     used to derive a mixin from.
  ///
  /// See dartbug.com/31542 for details of the semantics.
  bool get enableSuperMixins => false;

  /// Perform target-specific transformations on the outlines stored in
  /// [Component] when generating summaries.
  ///
  /// This transformation is used to add metadata on outlines and to filter
  /// unnecessary information before generating program summaries. This
  /// transformation is not applied when compiling full kernel programs to
  /// prevent affecting the internal invariants of the compiler and accidentally
  /// slowing down compilation.
  void performOutlineTransformations(Component component) {}

  /// Perform target-specific transformations on the given libraries that must
  /// run before constant evaluation.
  void performPreConstantEvaluationTransformations(
      Component component,
      CoreTypes coreTypes,
      List<Library> libraries,
      DiagnosticReporter diagnosticReporter,
      {void Function(String msg)? logger,
      ChangedStructureNotifier? changedStructureNotifier}) {}

  /// Perform target-specific modular transformations on the given libraries.
  void performModularTransformationsOnLibraries(
      Component component,
      CoreTypes coreTypes,
      ClassHierarchy hierarchy,
      List<Library> libraries,
      // TODO(askesc): Consider how to generally pass compiler options to
      // transformations.
      Map<String, String> environmentDefines,
      DiagnosticReporter diagnosticReporter,
      ReferenceFromIndex referenceFromIndex,
      {void logger(String msg),
      ChangedStructureNotifier changedStructureNotifier});

  /// Perform target-specific modular transformations on the given program.
  ///
  /// This is used when an individual expression is compiled, e.g. for debugging
  /// purposes. It is illegal to modify any of the enclosing nodes of the
  /// procedure.
  void performTransformationsOnProcedure(
      CoreTypes coreTypes, ClassHierarchy hierarchy, Procedure procedure,
      {void Function(String msg)? logger}) {}

  /// Whether a platform library may define a restricted type, such as `bool`,
  /// `int`, `double`, `num`, and `String`.
  ///
  /// By default only `dart:core` may define restricted types, but some target
  /// implementations override this.
  bool mayDefineRestrictedType(Uri uri) =>
      uri.scheme == 'dart' && uri.path == 'core';

  /// Whether a library is allowed to import a platform private library.
  ///
  /// By default only `dart:*` libraries are allowed. May be overridden for
  /// testing purposes.
  bool allowPlatformPrivateLibraryAccess(Uri importer, Uri imported) =>
      imported.scheme != "dart" ||
      !imported.path.startsWith("_") ||
      importer.scheme == "dart" ||
      (importer.scheme == "package" &&
          importer.path.startsWith("dart_internal/"));

  /// Whether the `native` language extension is supported within [library].
  ///
  /// The `native` language extension is not part of the language specification,
  /// it means something else to each target, and it is enabled under different
  /// circumstances for each target implementation. For example, the VM target
  /// enables it everywhere because of existing support for "dart-ext:" native
  /// extensions, but targets like dart2js only enable it on the core libraries.
  bool enableNative(Uri uri) => false;

  /// There are two variants of the `native` language extension. The VM expects
  /// the native token to be followed by string, whereas dart2js and DDC do not.
  // TODO(sigmund, ahe): ideally we should remove the `native` syntax, if not,
  // we should at least unify the VM and non-VM variants.
  bool get nativeExtensionExpectsString => false;

  /// Whether integer literals that cannot be represented exactly on the web
  /// (i.e. in Javascript) should cause an error to be issued.
  /// An example of such a number is `2^53 + 1` where in Javascript - because
  /// integers are represented as doubles
  /// `Math.pow(2, 53) = Math.pow(2, 53) + 1`.
  bool get errorOnUnexactWebIntLiterals => false;

  /// Whether set literals are natively supported by this target. If set
  /// literals are not supported by the target, they will be desugared into
  /// explicit `Set` creation (for non-const set literals) or wrapped map
  /// literals (for const set literals).
  bool get supportsSetLiterals => true;

  /// Bit mask of [LateLowering] values for the late lowerings that should
  /// be performed by the CFE.
  ///
  /// For the selected lowerings, late fields and variables are encoded using
  /// fields, getter, setters etc. in a way that provide equivalent semantics.
  /// See `pkg/kernel/nnbd_api.md` for details.
  int get enabledLateLowerings;

  /// Returns `true` if the CFE should lower a late field given it
  /// [hasInitializer], [isFinal], and [isStatic].
  ///
  /// This is determined by the [enabledLateLowerings] mask.
  bool isLateFieldLoweringEnabled(
      {required bool hasInitializer,
      required bool isFinal,
      required bool isStatic}) {
    // ignore: unnecessary_null_comparison
    assert(hasInitializer != null);
    // ignore: unnecessary_null_comparison
    assert(isFinal != null);
    // ignore: unnecessary_null_comparison
    assert(isStatic != null);
    int mask = LateLowering.getFieldLowering(
        hasInitializer: hasInitializer, isFinal: isFinal, isStatic: isStatic);
    return enabledLateLowerings & mask != 0;
  }

  /// Returns `true` if the CFE should lower a late local variable given it
  /// [hasInitializer], [isFinal], and its type [isPotentiallyNullable].
  ///
  /// This is determined by the [enabledLateLowerings] mask.
  bool isLateLocalLoweringEnabled(
      {required bool hasInitializer,
      required bool isFinal,
      required bool isPotentiallyNullable}) {
    // ignore: unnecessary_null_comparison
    assert(hasInitializer != null);
    // ignore: unnecessary_null_comparison
    assert(isFinal != null);
    // ignore: unnecessary_null_comparison
    assert(isPotentiallyNullable != null);
    int mask = LateLowering.getLocalLowering(
        hasInitializer: hasInitializer,
        isFinal: isFinal,
        isPotentiallyNullable: isPotentiallyNullable);
    return enabledLateLowerings & mask != 0;
  }

  /// If `true`, the backend supports creation and checking of a sentinel value
  /// for uninitialized late fields and variables through the `createSentinel`
  /// and `isSentinel` methods in `dart:_internal`.
  ///
  /// If `true` this is used when [supportsLateFields] is `false`.
  bool get supportsLateLoweringSentinel;

  /// Whether static fields with initializers in nnbd libraries should be
  /// encoded using the late field lowering.
  bool get useStaticFieldLowering;

  /// Whether calls to getters and fields should be encoded as a .call
  /// invocation on a property get.
  ///
  /// If `false`, calls to getters and fields are encoded as method invocations
  /// with the accessed getter or field as the interface target.
  bool get supportsExplicitGetterCalls;

  bool get supportsNewMethodInvocationEncoding;

  /// Builds an expression that instantiates an [Invocation] that can be passed
  /// to [noSuchMethod].
  Expression instantiateInvocation(CoreTypes coreTypes, Expression receiver,
      String name, Arguments arguments, int offset, bool isSuper);

  Expression instantiateNoSuchMethodError(CoreTypes coreTypes,
      Expression receiver, String name, Arguments arguments, int offset,
      {bool isMethod: false,
      bool isGetter: false,
      bool isSetter: false,
      bool isField: false,
      bool isLocalVariable: false,
      bool isDynamic: false,
      bool isSuper: false,
      bool isStatic: false,
      bool isConstructor: false,
      bool isTopLevel: false});

  /// Configure the given [Component] in a target specific way.
  /// Returns the configured component.
  Component configureComponent(Component component) => component;

  // Configure environment defines in a target-specific way.
  Map<String, String> updateEnvironmentDefines(Map<String, String> map) => map;

  String toString() => 'Target($name)';

  Class? concreteListLiteralClass(CoreTypes coreTypes) => null;
  Class? concreteConstListLiteralClass(CoreTypes coreTypes) => null;

  Class? concreteMapLiteralClass(CoreTypes coreTypes) => null;
  Class? concreteConstMapLiteralClass(CoreTypes coreTypes) => null;

  Class? concreteIntLiteralClass(CoreTypes coreTypes, int value) => null;
  Class? concreteDoubleLiteralClass(CoreTypes coreTypes, double value) => null;
  Class? concreteStringLiteralClass(CoreTypes coreTypes, String value) => null;

  ConstantsBackend constantsBackend(CoreTypes coreTypes);
}

class NoneConstantsBackend extends ConstantsBackend {
  @override
  final bool supportsUnevaluatedConstants;

  const NoneConstantsBackend({required this.supportsUnevaluatedConstants});
}

class NoneTarget extends Target {
  final TargetFlags flags;

  NoneTarget(this.flags);

  @override
  int get enabledLateLowerings => flags.forceLateLoweringsForTesting;

  @override
  bool get supportsLateLoweringSentinel =>
      flags.forceLateLoweringSentinelForTesting;

  @override
  bool get useStaticFieldLowering => flags.forceStaticFieldLoweringForTesting;

  @override
  bool get supportsExplicitGetterCalls =>
      !flags.forceNoExplicitGetterCallsForTesting;

  @override
  bool get supportsNewMethodInvocationEncoding => true;

  @override
  String get name => 'none';

  @override
  List<String> get extraRequiredLibraries => <String>[];

  @override
  void performModularTransformationsOnLibraries(
      Component component,
      CoreTypes coreTypes,
      ClassHierarchy hierarchy,
      List<Library> libraries,
      Map<String, String> environmentDefines,
      DiagnosticReporter diagnosticReporter,
      ReferenceFromIndex referenceFromIndex,
      {void Function(String msg)? logger,
      ChangedStructureNotifier? changedStructureNotifier}) {}

  @override
  Expression instantiateInvocation(CoreTypes coreTypes, Expression receiver,
      String name, Arguments arguments, int offset, bool isSuper) {
    return new InvalidExpression(null);
  }

  @override
  Expression instantiateNoSuchMethodError(CoreTypes coreTypes,
      Expression receiver, String name, Arguments arguments, int offset,
      {bool isMethod: false,
      bool isGetter: false,
      bool isSetter: false,
      bool isField: false,
      bool isLocalVariable: false,
      bool isDynamic: false,
      bool isSuper: false,
      bool isStatic: false,
      bool isConstructor: false,
      bool isTopLevel: false}) {
    return new InvalidExpression(null);
  }

  @override
  ConstantsBackend constantsBackend(CoreTypes coreTypes) =>
      // TODO(johnniwinther): Should this vary with the use case?
      const NoneConstantsBackend(supportsUnevaluatedConstants: true);
}

class LateLowering {
  static const int nullableUninitializedNonFinalLocal = 1 << 0;
  static const int nonNullableUninitializedNonFinalLocal = 1 << 1;
  static const int nullableUninitializedFinalLocal = 1 << 2;
  static const int nonNullableUninitializedFinalLocal = 1 << 3;
  static const int nullableInitializedNonFinalLocal = 1 << 4;
  static const int nonNullableInitializedNonFinalLocal = 1 << 5;
  static const int nullableInitializedFinalLocal = 1 << 6;
  static const int nonNullableInitializedFinalLocal = 1 << 7;
  static const int uninitializedNonFinalStaticField = 1 << 8;
  static const int uninitializedFinalStaticField = 1 << 9;
  static const int initializedNonFinalStaticField = 1 << 10;
  static const int initializedFinalStaticField = 1 << 11;
  static const int uninitializedNonFinalInstanceField = 1 << 12;
  static const int uninitializedFinalInstanceField = 1 << 13;
  static const int initializedNonFinalInstanceField = 1 << 14;
  static const int initializedFinalInstanceField = 1 << 15;

  static const int none = 0;
  static const int all = (1 << 16) - 1;

  static int getLocalLowering(
      {required bool hasInitializer,
      required bool isFinal,
      required bool isPotentiallyNullable}) {
    // ignore: unnecessary_null_comparison
    assert(hasInitializer != null);
    // ignore: unnecessary_null_comparison
    assert(isFinal != null);
    // ignore: unnecessary_null_comparison
    assert(isPotentiallyNullable != null);
    if (hasInitializer) {
      if (isFinal) {
        if (isPotentiallyNullable) {
          return nullableInitializedFinalLocal;
        } else {
          return nonNullableInitializedFinalLocal;
        }
      } else {
        if (isPotentiallyNullable) {
          return nullableInitializedNonFinalLocal;
        } else {
          return nonNullableInitializedNonFinalLocal;
        }
      }
    } else {
      if (isFinal) {
        if (isPotentiallyNullable) {
          return nullableUninitializedFinalLocal;
        } else {
          return nonNullableUninitializedFinalLocal;
        }
      } else {
        if (isPotentiallyNullable) {
          return nullableUninitializedNonFinalLocal;
        } else {
          return nonNullableUninitializedNonFinalLocal;
        }
      }
    }
  }

  static int getFieldLowering(
      {required bool hasInitializer,
      required bool isFinal,
      required bool isStatic}) {
    // ignore: unnecessary_null_comparison
    assert(hasInitializer != null);
    // ignore: unnecessary_null_comparison
    assert(isFinal != null);
    // ignore: unnecessary_null_comparison
    assert(isStatic != null);
    if (hasInitializer) {
      if (isFinal) {
        if (isStatic) {
          return initializedFinalStaticField;
        } else {
          return initializedFinalInstanceField;
        }
      } else {
        if (isStatic) {
          return initializedNonFinalStaticField;
        } else {
          return initializedNonFinalInstanceField;
        }
      }
    } else {
      if (isFinal) {
        if (isStatic) {
          return uninitializedFinalStaticField;
        } else {
          return uninitializedFinalInstanceField;
        }
      } else {
        if (isStatic) {
          return uninitializedNonFinalStaticField;
        } else {
          return uninitializedNonFinalInstanceField;
        }
      }
    }
  }
}