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[ddc] Avoid weak mode warning in FutureOr casts

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This is not intended to change the result of the cast in any mode.

An optimization for casting null in weak mode accidentally added
warnings when casting to a FutureOr (non-nullable) of a legacy
type.

Also moves the `is` and `as` methods for FutureOr types from being
hard-coded in the compiler to the runtime method that builds the
type.

Tested on golem and found no attributable performance regressions:
https://golem.corp.goog/Comparison?team=dartdevc#targetA%3Ddartdevc-null%3BmachineTypeA%3Dlinux-x64%3BrevisionA%3D88970%3BpatchA%3Dnshahan-FutureOr-Fix%3BtargetB%3Ddartdevc-null%3BmachineTypeB%3Dlinux-x64%3BrevisionB%3D88964%3BpatchB%3DNone

Change-Id: I44a23c7e2e1d15bc6c383fc95b19f99b584a3f7a
Fixes: https://github.com/dart-lang/sdk/issues/43990
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/170001
Reviewed-by: Mark Zhou <markzipan@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>
This commit is contained in:
Nicholas Shahan 2020-11-02 21:45:09 +00:00 committed by commit-bot@chromium.org
parent 53c82cbc4b
commit ab7dc265d7
2 changed files with 25 additions and 23 deletions
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25
pkg/dev_compiler/lib/src/kernel/compiler.dart
View file

@ -1082,29 +1082,8 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
}
if (c == _coreTypes.deprecatedFutureOrClass) {
// These methods are difficult to place in the runtime or patch files.
// * They need to be callable from the class but they can't be static
// methods on the FutureOr class in Dart because they reference the
// generic type parameter.
// * There isn't an obvious place in dart:_runtime were we could place a
// method that adds these type tests (similar to addTypeTests()) because
// in the bootstrap ordering the Future class hasn't been defined yet.
var typeParam =
TypeParameterType(c.typeParameters[0], Nullability.undetermined);
var typeT = visitTypeParameterType(typeParam);
var futureOfT = visitInterfaceType(InterfaceType(
_coreTypes.futureClass, currentLibrary.nonNullable, [typeParam]));
body.add(js.statement('''
#.is = function is_FutureOr(o) {
return #.is(o) || #.is(o);
}
''', [className, typeT, futureOfT]));
body.add(js.statement('''
#.as = function as_FutureOr(o) {
if (#.is(o) || #.is(o)) return o;
return #.as(o, this);
}
''', [className, typeT, futureOfT, runtimeModule]));
// Custom type tests for FutureOr types are attached when the type is
// constructed in the runtime normalizeFutureOr method.
return null;
}

23
sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/classes.dart
View file

@ -164,6 +164,29 @@ normalizeFutureOr(typeConstructor, setBaseClass) {
// as a FutureOr because it is equal to 'async.FutureOr` (in the JS).
JS('!', '#[#] = #', genericType, _originalDeclaration, normalize);
JS('!', '#(#)', addTypeCaches, genericType);
// Add FutureOr specific is and as methods.
is_FutureOr(obj) =>
JS<bool>('!', '#.is(#)', typeArg, obj) ||
JS<bool>('!', '#(#).is(#)', getGenericClass(Future), typeArg, obj);
JS('!', '#.is = #', genericType, is_FutureOr);
as_FutureOr(obj) {
// Special test to handle case for mixed mode non-nullable FutureOr of a
// legacy type. This allows casts like `null as FutureOr<int*>` to work
// in weak and sound mode.
if (obj == null && _jsInstanceOf(typeArg, LegacyType)) {
return obj;
}
if (JS<bool>('!', '#.is(#)', typeArg, obj) ||
JS<bool>('!', '#(#).is(#)', getGenericClass(Future), typeArg, obj)) {
return obj;
}
return cast(obj, JS('!', '#(#)', getGenericClass(FutureOr), typeArg));
}
JS('!', '#.as = #', genericType, as_FutureOr);
return genericType;
}