commit 8de00e213755d358ef5322af6f5ca97fe711776b
author Daco Harkes <dacoharkes@google.com> Thu Mar 07 18:33:58 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Mar 07 18:33:58 2024 +0000
tree 15ea5b6d58db2c83fc58d71baead6ce0dd8d8bbc
parent 094202bb91f881e7a4a3b44246842dfed9370fce

[vm] Introduce pragma `vm:deeply-immutable`

This CL introduces a way to mark all instances of a class as deeply
immutable.

In order to statically verify that all instances of a deeply immutable
class are immutable, a deeply immutable classes must have the following
properties:

1. All instance fields must
   1. have a deeply immutable type,
   2. be final, and
   3. be non-late.
2. The class must be `final` or `sealed`. This ensures no
   non-deeply-immutable subtypes are added by external code.
3. All subtypes must be deeply immutable. This ensures 1.1 can be
   trusted.
4. The super type must be deeply immutable (except for Object).

Note that instances of some classes in the VM are deeply immutable
while their class cannot be marked immutable.

* SendPort, Capability, RegExp, and StackTrace are not `final` and
  can be implemented by external code.
* UnmodifiableTypedDataViews do not have a public type. (It was
  recently deprecated.)

See runtime/docs/deeply_immutable.md for more details.

Use case:

This enables attaching a `Dart_FinalizableHandle` to a deeply immutable
object and the deeply immutable object with other isolates in the same
isolate group.

(Note that `NativeFinalizer`s live in an isolate, and not an isolate
group. So this should currently _not_ be used with `NativeFinalizer`s.
See https://github.com/dart-lang/sdk/issues/55062 for making a
`NativeFinalizer.shared(` that would live in an isolate group instead
of in an isolate.)

Implementation details:

Before this CL, the `ImmutableBit` in the object header was only ever
set to true for predefined class ids (and for const objects). After
this CL, the bit can also be set to true for non const instances of
user-defined classes. The object allocation and initialization code has
been changed to deal with this new case. The immutability of a class is
saved in the class state bits. On object allocation and initialization
the immutability bit is read from the class for non-predefined class
ids.

TEST=runtime/tests/vm/dart/isolates/fast_object_copy2_test.dart
TEST=runtime/vm/isolate_reload_test.cc
TEST=tests/lib/isolate/deeply_immutable_*

Bug: https://github.com/dart-lang/sdk/issues/55120
Bug: https://github.com/dart-lang/sdk/issues/54885
Change-Id: Ib97fe589cb4f81673cb928c93e3093838d82132d
Cq-Include-Trybots: luci.dart.try:vm-aot-android-release-arm64c-try,vm-aot-android-release-arm_x64-try,vm-aot-linux-debug-x64-try,vm-aot-linux-debug-x64c-try,vm-aot-mac-release-arm64-try,vm-aot-mac-release-x64-try,vm-aot-obfuscate-linux-release-x64-try,vm-aot-optimization-level-linux-release-x64-try,vm-appjit-linux-debug-x64-try,vm-asan-linux-release-x64-try,vm-checked-mac-release-arm64-try,vm-eager-optimization-linux-release-ia32-try,vm-eager-optimization-linux-release-x64-try,vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64c-try,vm-ffi-qemu-linux-release-arm-try,vm-ffi-qemu-linux-release-riscv64-try,vm-fuchsia-release-x64-try,vm-kernel-linux-debug-x64-try,vm-kernel-precomp-linux-release-x64-try,vm-linux-debug-ia32-try,vm-linux-debug-x64-try,vm-linux-debug-x64c-try,vm-mac-debug-arm64-try,vm-mac-debug-x64-try,vm-msan-linux-release-x64-try,vm-reload-linux-debug-x64-try,vm-reload-rollback-linux-debug-x64-try,vm-ubsan-linux-release-x64-try
Cq-Include-Trybots: dart-internal/g3.dart-internal.try:g3-cbuild-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/354902
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>