Implement stringref operations

[dcodeIO]

Implements the current state of the Reference-Typed Strings proposal (currently phase 1) as supported by Binaryen, for now as built-ins to enable experimentation. A constant reference-typed string can be created using a string literal in a ref_string context.

Enable with --enable stringref in AS, --experimental-wasm-stringref in V8.

Instruction	Binaryen status
string.const	✔️
string.new_utf8	⏳ Assumes single memory
string.new_utf8_array	✔️
string.new_lossy_utf8	⏳ Assumes single memory
string.new_lossy_utf8_array	✔️
string.new_wtf8	⏳ Assumes single memory
string.new_wtf8_array	✔️
string.new_wtf16	⏳ Assumes single memory
string.new_wtf16_array	✔️
string.from_code_point	✔️
string.hash	✔️
string.measure_utf8	✔️
string.measure_wtf8	✔️
string.measure_wtf16	✔️
string.is_usv_sequence	✔️
string.encode_utf8	⏳ Assumes single memory
string.encode_utf8_array	✔️
string.encode_lossy_utf8	❌
string.encode_lossy_utf8_array	❌
string.encode_wtf8	⏳ Assumes single memory
string.encode_wtf8_array	✔️
string.encode_wtf16	⏳ Assumes single memory
string.encode_wtf16_array	✔️
string.concat	✔️
string.eq	✔️
string.compare	✔️
string.as_wtf8	✔️
string.as_wtf16	✔️
string.as_iter	✔️
stringview_wtf8.advance	✔️
stringview_wtf8.encode_utf8	❌
stringview_wtf8.encode_lossy_utf8	❌
stringview_wtf8.encode_wtf8	❌
stringview_wtf8.slice	✔️
stringview_wtf16.length	✔️
stringview_wtf16.slice	✔️
stringview_wtf16.get_codeunit	✔️
stringview_wtf16.encode	❌
stringview_iter.next	✔️
stringview_iter.advance	✔️
stringview_iter.rewind	✔️
stringview_iter.slice	✔️

✔️ Available   ⏳ Available but incomplete   ❌ Not available

Possible follow-up work in case there is interest: Populate the RefString wrapper class using the instructions to mimic String, so it can eventually replace String. So far this PR implements a few string functions as a POC.

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[dcodeIO]

With #2689 in place, instructions that technically accept but would throw when provided a stringref that is null now take ref_string (non-nullable stringref), effectively eliminating the possibility of such traps statically per the type system. Similarly, instructions that cannot produce null use ref_string as their return type, with tests showing that V8 materializes a non-nullable type there as well, i.e. respective assignments succeeding. One exception is string.eq, as it can deal with null inputs.

[dcodeIO]

There is some proof of concept code now, showing how RefString can be populated with functionality utilizing the stringref instruction set. Basically, in a ref_string type context, a string literal compiles to a string.const, making a reference-typed string. Such a value of type ref_string is backed by the RefString wrapper class (in std/assembly/references.ts) providing the JS-like API that mostly vanishes after optimizations, leaving primarily the string instructions. So the underlying Wasm type in AS is simply (ref string) that can be exchanged with JS and Web APIs by reference.

[dcodeIO]

Quick update: There has been a more general string discussion in CG context meanwhile. Iiuc, an alternative to stringref that instead uses (non-portable?) compile time imports for common string operations has been discussed. Also noteworthy:

The Wasmtime project would prefer not to implement stringref. We don't have a managed host string to expose to Wasm guests, and we don't want to have to implement one. We would rather that Wasm guests implement their own strings on top of the GC proposal, where they can build exactly what they need, which can be very different across languages. As far as interoperability of strings across different languages goes, we believe this should be addressed at the component model and interface types layer. For tight integration with JS strings on the Web, string imports seem like a good solution.

Translated: Our thing that intentionally does not address the thing should be off-label responsible for the thing so we can not address the thing and eventually the Web becomes the special case - it's BusinessWasmtime!

[github-actions]

This PR has been automatically marked as stale because it has not had recent activity. It will be closed in one week if no further activity occurs. Thank you for your contributions!

[github-actions]

This PR has been automatically closed due to lack of recent activity, but feel free to reopen it as long as you merge in the main branch afterwards.

[github-actions]

This PR has been automatically marked as stale because it has not had recent activity. It will be closed in one week if no further activity occurs. Thank you for your contributions!

[github-actions]

This PR has been automatically closed due to lack of recent activity, but feel free to reopen it as long as you merge in the main branch afterwards.