commit 57a1168875ad9bb0c944d4077ba71b3dac5a1e74
author Tess Strickland <sstrickl@google.com> Thu Jan 04 14:44:29 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Jan 04 14:44:29 2024 +0000
tree 2b28d2f916d46f8fd8f9d6a591be4d8c2a39c050
parent 91d16af92bbd905f95ae7ca6abb59588145f2220

[pkg/vm] Create @pragma("vm:platform-const-if", <cond>) annotation

If a static field or getter is annotated with
@pragma("vm:platform-const-if", <cond>) and <cond> const evaluates
to true, then uses of the static field or getter are const evaluated
when a target operating system is available. If <cond> const evaluates
to any other value, then the annotation is ignored.

For example, when runtime-only code is guarded like the following,
using Flutter's kDebugMode constant, then debug mode Flutter programs
can alter the defaultTargetPlatform for testing, but in release mode,
the defaultTargetPlatform getter is const evaluated and code guarded
with defaultTargetPlatform checks can be eliminated if unreachable:

  @pragma("vm:platform-const-if", !kDebugMode)
  TargetPlatform get defaultTargetPlatform {
   ...
   assert(() {
     if (Platform.environment.containsKey('FLUTTER_TEST')) {
       result = TestPlatform.android;
     }
     return true;
   }());
   if (kDebugMode &&
       platform.debugDefaultTargetPlatformOverride != null) {
     result = platform.debugDefaultTargetPlatformOverride;
   }
   ...
  }

TEST=pkg/vm/test/transformations/vm_constant_evaluator

Change-Id: I55b88502a908c56cf42a761dd06741f15c8a23d9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/333220
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>