🪙 Value text encoding ambiguities / quirks

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
38/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
wasm
Domain
compilers

Research direction

Start with the value definitions section in design/mvp/Explainer.md and compare its val rules with the WAVE mapping and the referenced value definitions. Trace the char, float, handle, and integer cases, then determine the intended grammar and validation behavior for each ambiguity. Done means the specification has an agreed, unambiguous treatment of the reported cases.

Written by the indexing model from the issue text.

Description

In looking at WAVE mapping to value defs (ref https://github.com/WebAssembly/component-model/pull/639#issuecomment-4292311870) I found some quirks in the val rules:

  • char
    • Allows unescaped single quote (value char '''), which is unambiguous in context but seems awkward to parse and confusing to read (especially if you're used to Python!).
    • Rejects unescaped double-quote ('"'), which is slightly annoying to me, personally. 🙂
  • floats
    • f32 is encoded as core:f64 which leaves rounding and overflow ambiguous, e.g. core:f64 accepts 1e99 which will overflow an f32.
    • f64canon rejects nan:0x but not -nan
  • Handles in variants:
    • Currently this would seem to be valid: (value (option (future)) none), which is at least surprising if not actually wrong.
  • Ints:
    • Depending on how I squint it looks like (value u64 -1) might be valid via core:i64 (wrapping to u64::MAX).

Separately: the bottom of the value definitions section describes value imports/exports but the import/export defs are missing matching rules. Nope, I was looking in the wrong place.

Dominant language
WebAssembly
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