sdk/lib/_internal/js_runtime/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, JsBuiltin;
import 'dart:_rti' show Rti;

/// Emits a JavaScript code fragment parametrized 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 corresponding 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.
///
///
/// Type argument.
///
/// In Dart 2.0, the type argument additionally constrains the returned type.
/// So, with type inference filling in the type argumemnt,
///
///     String s = JS('', 'JSON.stringify(#)', x);
///
/// will be the same as the current meaning of
///
///     var s = JS('String|Null', 'JSON.stringify(#)', x);
///
///
/// 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.
external T JS<T>(String typeDescription, String codeTemplate,
    [arg0,
    arg1,
    arg2,
    arg3,
    arg4,
    arg5,
    arg6,
    arg7,
    arg8,
    arg9,
    arg10,
    arg11,
    arg12,
    arg13,
    arg14,
    arg51,
    arg16,
    arg17,
    arg18,
    arg19]);

/// 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.
external 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.
external RAW_DART_FUNCTION_REF(Function function);

/// 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)`.
external JS_INTERCEPTOR_CONSTANT(Type type);

/// Returns the interceptor for [object].
///
/// Calls are replaced with the [HInterceptor] SSA instruction.
external getInterceptor(object);

/// Returns the Rti object for the type for JavaScript arrays via JS-interop.
///
/// Calls are replaced with a [HLoadType] SSA instruction.
external Object getJSArrayInteropRti();

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

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

/// Instructs the compiler to execute the [builtinName] action at the call-site.
///
/// The [builtin] should be a constant defined in the `_embedded_names`
/// library.
// Add additional optional arguments if needed. The method is treated internally
// as a variable argument method.
external JS_BUILTIN(String typeDescription, JsBuiltin builtin,
    [arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11]);

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

/// Returns a TypeReference to [T].
external Rti TYPE_REF<T>();

/// Returns a TypeReference to [T]*.
external Rti LEGACY_TYPE_REF<T>();

/// 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);
}

/// Creates a JavaScript value that can be used as a sentinel for uninitialized
/// late fields and variables.
external T createJsSentinel<T>();

/// Returns `true` if [value] is the sentinel JavaScript value created through
/// [createJsSentinel].
external bool isJsSentinel(dynamic value);