dart/sdk/lib/_internal/compiler/js_lib/foreign_helper.dart

// Copyright (c) 2012, 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 _foreign_helper;

import 'dart:_js_embedded_names' show JsGetName;

/**
 * Emits a JavaScript code fragment parameterized by arguments.
 *
 * Hash characters `#` in the [codeTemplate] are replaced in left-to-right order
 * with expressions that contain the values of, or evaluate to, the arguments.
 * The number of hash marks must match the number or arguments.  Although
 * declared with arguments [arg0] through [arg2], the form actually has no limit
 * on the number of arguments.
 *
 * The [typeDescription] argument is interpreted as a description of the
 * behavior of the JavaScript code.  Currently it describes the side effects
 * types that may be returned by the expression, with the additional behavior
 * that the returned values may be fresh instances of the types.  The type
 * information must be correct as it is trusted by the compiler in
 * optimizations, and it must be precise as possible since it is used for native
 * live type analysis to tree-shake large parts of the DOM libraries.  If poorly
 * written, the [typeDescription] will cause unnecessarily bloated programs.
 * (You can check for this by compiling with `--verbose`; there is an info
 * message describing the number of native (DOM) types that can be removed,
 * which usually should be greater than zero.)
 *
 * The [typeDescription] must be a [String]. Two forms of it are supported:
 *
 * 1) a union of types separated by vertical bar `|` symbols, e.g.
 *    `"num|String"` describes the union of numbers and Strings.  There is no
 *    type in Dart that is this precise.  The Dart alternative would be `Object`
 *    or `dynamic`, but these types imply that the JS-code might also be
 *    creating instances of all the DOM types.
 *
 *    If `null` is possible, it must be specified explicitly, e.g.
 *    `"String|Null"`. [typeDescription] has several extensions to help describe
 *    the behavior more accurately.  In addition to the union type already
 *    described:
 *
 *    + `=Object` is a plain JavaScript object.  Some DOM methods return
 *       instances that have no corresponing Dart type (e.g. cross-frame
 *       documents), `=Object` can be used to describe these untyped' values.
 *
 *    + `var` (or empty string).  If the entire [typeDescription] is `var` (or
 *      empty string) then the type is `dynamic` but the code is known to not
 *      create any instances.
 *
 *   Examples:
 *
 *       // Parent window might be an opaque cross-frame window.
 *       var thing = JS('=Object|Window', '#.parent', myWindow);
 *
 * 2) a sequence of the form `<tag>:<value>;` where `<tag>` is one of
 *    `creates`, `returns`, `effects` or `depends`.
 *
 *    The first two tags are used to specify the created and returned types of
 *    the expression. The value of `creates` and `returns` is a type string as
 *    defined in 1).
 *
 *    The tags `effects` and `depends` encode the side effects of this call.
 *    They can be omitted, in which case the expression is parsed and a safe
 *    conservative side-effect estimation is computed.
 *
 *    The values of `effects` and `depends` may be 'all', 'none' or a
 *    comma-separated list of 'no-index', 'no-instance' and 'no-static'.
 *
 *    The value 'all' indicates that the call affects/depends on every
 *    side-effect. The flag 'none' signals that the call does not affect
 *    (resp. depends on) anything.
 *
 *    The value 'no-index' indicates that the call does *not* do (resp. depends
 *    on) any array index-store. The flag 'no-instance' indicates that the call
 *    does not modify (resp. depends on) any instance variable. Similarly,
 *    the 'no-static' value indicates that the call does not modify (resp.
 *    depends on) any static variable.
 *
 *    The `effects` and `depends` flag must be used in tandem. Either both are
 *    specified or none is.
 *
 *    Each tag (including the type tags) may only occur once in the sequence.
 *
 * Guidelines:
 *
 *  + Do not use any parameter, local, method or field names in the
 *    [codeTemplate].  These names are all subject to arbitrary renaming by the
 *    compiler.  Pass the values in via `#` substition, and test with the
 *    `--minify` dart2js command-line option.
 *
 *  + The substituted expressions are values, not locations.
 *
 *        JS('void', '# += "x"', this.field);
 *
 *    `this.field` might not be a substituted as a reference to the field.  The
 *    generated code might accidentally work as intended, but it also might be
 *
 *        var t1 = this.field;
 *        t1 += "x";
 *
 *    or
 *
 *        this.get$field() += "x";
 *
 *    The remedy in this case is to expand the `+=` operator, leaving all
 *    references to the Dart field as Dart code:
 *
 *        this.field = JS('String', '# + "x"', this.field);
 *
 *  + Never use `#` in function bodies.
 *
 *    This is a variation on the previous guideline.  Since `#` is replaced with
 *    an *expression* and the expression is only valid in the immediate context,
 *    `#` should never appear in a function body.  Doing so might defer the
 *    evaluation of the expression, and its side effects, until the function is
 *    called.
 *
 *    For example,
 *
 *        var value = foo();
 *        var f = JS('', 'function(){return #}', value)
 *
 *    might result in no immediate call to `foo` and a call to `foo` on every
 *    call to the JavaScript function bound to `f`.  This is better:
 *
 *        var f = JS('',
 *            '(function(val) { return function(){return val}; })(#)', value);
 *
 *    Since `#` occurs in the immediately evaluated expression, the expression
 *    is immediately evaluated and bound to `val` in the immediate call.
 *
 *
 * Additional notes.
 *
 * In the future we may extend [typeDescription] to include other aspects of the
 * behavior, for example, separating the returned types from the instantiated
 * types to allow the compiler to perform more optimizations around the code.
 *
 * This might be an extension of [JS] or a new function similar to [JS] with
 * additional arguments for the new information.
 */
// Add additional optional arguments if needed. The method is treated internally
// as a variable argument method.
JS(String typeDescription, String codeTemplate,
    [arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11])
{}

/**
 * Returns the isolate in which this code is running.
 */
IsolateContext JS_CURRENT_ISOLATE_CONTEXT() {}

abstract class IsolateContext {
  /// Holds a (native) JavaScript instance of Isolate, see
  /// finishIsolateConstructorFunction in emitter.dart.
  get isolateStatics;
}

/**
 * Invokes [function] in the context of [isolate].
 */
JS_CALL_IN_ISOLATE(isolate, Function function) {}

/**
 * Converts the Dart closure [function] into a JavaScript closure.
 *
 * Warning: This is no different from [RAW_DART_FUNCTION_REF] which means care
 * must be taken to store the current isolate.
 */
DART_CLOSURE_TO_JS(Function function) {}

/**
 * Returns a raw reference to the JavaScript function which implements
 * [function].
 *
 * Warning: this is dangerous, you should probably use
 * [DART_CLOSURE_TO_JS] instead. The returned object is not a valid
 * Dart closure, does not store the isolate context or arity.
 *
 * A valid example of where this can be used is as the second argument
 * to V8's Error.captureStackTrace. See
 * https://code.google.com/p/v8/wiki/JavaScriptStackTraceApi.
 */
RAW_DART_FUNCTION_REF(Function function) {}

/**
 * Sets the current isolate to [isolate].
 */
void JS_SET_CURRENT_ISOLATE(isolate) {}

/**
 * Returns the JavaScript constructor function for Dart's Object class.
 * This can be used for type tests, as in
 *
 *     if (JS('bool', '# instanceof #', obj, JS_DART_OBJECT_CONSTRUCTOR()))
 *       ...
 */
JS_DART_OBJECT_CONSTRUCTOR() {}

/**
 * Returns the interceptor for class [type].  The interceptor is the type's
 * constructor's `prototype` property.  [type] will typically be the class, not
 * an interface, e.g. `JS_INTERCEPTOR_CONSTANT(JSInt)`, not
 * `JS_INTERCEPTOR_CONSTANT(int)`.
 */
JS_INTERCEPTOR_CONSTANT(Type type) {}

/**
 * Returns the prefix used for generated is checks on classes.
 */
String JS_OPERATOR_IS_PREFIX() {}

/**
 * Returns the prefix used for generated type argument substitutions on classes.
 */
String JS_OPERATOR_AS_PREFIX() {}

/// Returns the name of the class `Object` in the generated code.
String JS_OBJECT_CLASS_NAME() {}

/// Returns the name of the class `Null` in the generated code.
String JS_NULL_CLASS_NAME() {}

/// Returns the name of the class `Function` in the generated code.
String JS_FUNCTION_CLASS_NAME() {}

/**
 * Returns the field name used for determining if an object or its
 * interceptor has JavaScript indexing behavior.
 */
String JS_IS_INDEXABLE_FIELD_NAME() {}

/**
 * Returns the object corresponding to Namer.CURRENT_ISOLATE.
 */
JS_CURRENT_ISOLATE() {}

/// Returns the name used for generated function types on classes and methods.
String JS_SIGNATURE_NAME() {}

/// Returns the name used to tag typedefs.
String JS_TYPEDEF_TAG() {}

/// Returns the name used to tag function type representations in JavaScript.
String JS_FUNCTION_TYPE_TAG() {}

/**
 * Returns the name used to tag void return in function type representations
 * in JavaScript.
 */
String JS_FUNCTION_TYPE_VOID_RETURN_TAG() {}

/**
 * Returns the name used to tag return types in function type representations
 * in JavaScript.
 */
String JS_FUNCTION_TYPE_RETURN_TYPE_TAG() {}

/**
 * Returns the name used to tag required parameters in function type
 * representations in JavaScript.
 */
String JS_FUNCTION_TYPE_REQUIRED_PARAMETERS_TAG() {}

/**
 * Returns the name used to tag optional parameters in function type
 * representations in JavaScript.
 */
String JS_FUNCTION_TYPE_OPTIONAL_PARAMETERS_TAG() {}

/**
 * Returns the name used to tag named parameters in function type
 * representations in JavaScript.
 */
String JS_FUNCTION_TYPE_NAMED_PARAMETERS_TAG() {}

/// Returns the JS name for [name] from the Namer.
String JS_GET_NAME(JsGetName name) {}

/// Reads an embedded global.
///
/// The [name] should be a constant defined in the `_embedded_names` library.
JS_EMBEDDED_GLOBAL(String typeDescription, String name) {}

/// Returns the state of a flag that is determined by the state of the compiler
/// when the program has been analyzed.
bool JS_GET_FLAG(String name) {}

/**
 * Pretend [code] is executed.  Generates no executable code.  This is used to
 * model effects at some other point in external code.  For example, the
 * following models an assignment to foo with an unknown value.
 *
 *     var foo;
 *
 *     main() {
 *       JS_EFFECT((_){ foo = _; })
 *     }
 *
 * TODO(sra): Replace this hack with something to mark the volatile or
 * externally initialized elements.
 */
void JS_EFFECT(Function code) { code(null); }

/**
 * Use this class for creating constants that hold JavaScript code.
 * For example:
 *
 * const constant = JS_CONST('typeof window != "undefined");
 *
 * This code will generate:
 * $.JS_CONST_1 = typeof window != "undefined";
 */
class JS_CONST {
  final String code;
  const JS_CONST(this.code);
}

/**
 * JavaScript string concatenation. Inputs must be Strings.  Corresponds to the
 * HStringConcat SSA instruction and may be constant-folded.
 */
String JS_STRING_CONCAT(String a, String b) {
  // This body is unused, only here for type analysis.
  return JS('String', '# + #', a, b);
}