1825088 - Add support for final types in GC proposal

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, task, P3)

Description

[Ryan Hunt [:rhunt]]

The GC proposal now supports marking some type definitions as 'final' which means that no type may declare themselves a subtype of that one. [1]

The motivation for this is that when you downcast to a final type, you can just compare the object's type definition directly without doing a full subtype check.

To support this we need:

1. Update wasm-tools to parse and encode a final flag
2. Add a 'isFinal' flag to wasm::TypeDef
3. Don't allow a type to declare a parent type that is final (see TypeDef::canBeSubtypeOf)
4. Decode the 'isFinal' flag while reading type definitions (see DecodeTypeSection)

[1] https://github.com/WebAssembly/gc/blob/main/proposals/gc/MVP.md#type-definitions

Comment 1

[Julien Pages [:jpages]]

See https://github.com/bytecodealliance/wasm-tools/pull/1043

PR for final types is currently a draft and needs some changes in wasm-tools first: https://phabricator.services.mozilla.com/D178384

Comment 2

[Julien Pages [:jpages]]

Attachment: Bug 1825088 - wasm: Add support for final types. r=rhunt

A final type can't have any subtypes. All wasm types
are now final by default unless the sub keyword is used.
To make a type non final use: (type $foo (sub)).
Use final with the following syntax: (type $foo (sub final)).

Comment 3

[Julien Pages [:jpages]]

Attachment: Bug 1825088 - wasm: Bump crate versions for wast and wasm-smith. r=rhunt

Depends on D178384

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c910266f6c42
wasm: Add support for final types. r=rhunt

Comment 5

[Norisz Fay [:noriszfay]]

Backed out for causing SM bustages on br-on-cast.js

Backout link

Push with failures

Failure log

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/7d6d051e0abd
wasm: Add support for final types. r=rhunt

Comment 7

[Cristina Horotan [:chorotan]]

Backed out changeset 7d6d051e0abd (bug 1825088) for causing multiple failures

Backout: https://hg.mozilla.org/integration/autoland/rev/cbbbe12901352ad97e23bfb3d8bc8eb0b142635f

Failure push: https://treeherder.mozilla.org/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&revision=7d6d051e0abde1fbf8a2dfcacb630cedfc7d4a0a

Failure logs:
SM failure: https://treeherder.mozilla.org/logviewer?job_id=420637067&repo=autoland&lineNumber=14177
Jit failure: https://treeherder.mozilla.org/logviewer?job_id=420639027&repo=autoland&lineNumber=45289

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/e6b123be310c
wasm: Add support for final types. r=rhunt
https://hg.mozilla.org/integration/autoland/rev/c40b6292592f
wasm: Bump crate versions for wast and wasm-smith. r=rhunt,supply-chain-reviewers

Comment 9

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/e6b123be310c
https://hg.mozilla.org/mozilla-central/rev/c40b6292592f