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Update core type explainer text to match implementation #350

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May 11, 2024
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Update core type explainer text to match implementation #350

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3 changes: 0 additions & 3 deletions design/mvp/Binary.md
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Expand Up @@ -160,9 +160,6 @@ Notes:
initially-empty type index space.
* `alias` declarators currently only allow `outer` `type` aliases but
would add `export` aliases when core wasm adds type exports.
* Validation of `outer` aliases cannot see beyond the enclosing core type index
space. Since core modules and core module types cannot nest in the MVP, this
means that the maximum `ct` in an MVP `alias` declarator is `1`.

```ebnf
type ::= dt:<deftype> => (type dt)
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14 changes: 5 additions & 9 deletions design/mvp/Explainer.md
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Expand Up @@ -493,17 +493,13 @@ implicitly-created `func` type referring to both.
Lastly, the `core:alias` module declarator allows a module type definition to
reuse (rather than redefine) type definitions in the enclosing component's core
type index space via `outer` `type` alias. In the MVP, validation restricts
`core:alias` module declarators to *only* allow `outer` `type` aliases but,
in the future, more kinds of aliases would be meaningful and allowed.
`core:alias` module declarators to *only* allow `outer` `type` aliases (into an
enclosing component's or component-type's core type index space). In the
future, more kinds of aliases would be meaningful and allowed.

As an example, the following component defines two semantically-equivalent
module types, where the former defines the function type via `type` declarator
and the latter refers via `alias` declarator. Note that, since core type
definitions are validated in a Core WebAssembly context that doesn't "know"
anything about components, the module type `$C2` can't name `$C` directly in
the text format but must instead use the appropriate [de Bruijn] index (`1`).
In both cases, the defined/aliased function type is given index `0` since
module types always start with an empty type index space.
and the latter refers via `alias` declarator.
```wasm
(component $C
(core type $C1 (module
Expand All @@ -513,7 +509,7 @@ module types always start with an empty type index space.
))
(core type $F (func (param i32) (result i32)))
(core type $C2 (module
(alias outer 1 $F (type))
(alias outer $C $F (type))
(import "a" "b" (func (type 0)))
(export "c" (func (type 0)))
))
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