Add 'async' canonopt and 'task.*' built-ins

Author: lukewagner

README.md

@@ -2,10 +2,10 @@
 
 This repository is where the component model is being standardized. For a more user-focused explanation, take a look at the **[Component Model Documentation]**.
 
-This repository describes the high-level [goals], [use cases], [design choices]
-and [FAQ] of the component model as well as a more-detailed [assembly-level explainer], [IDL],
-[binary format] and [ABI] covering the initial Minimum Viable Product (MVP)
-release.
+This repository contains the high-level [goals], [use cases], [design choices]
+and [FAQ] of the component model as well as a more-detailed, low-level
+[AST explainer], [async explainer], [IDL], [binary format] and [ABI] covering
+the initial Minimum Viable Product (MVP) release.
 
 In the future, this repository will additionally contain a [formal spec],
 reference interpreter and test suite.
@@ -27,7 +27,8 @@ To contribute to any of these repositories, see the Community Group's
 [use cases]: design/high-level/UseCases.md
 [design choices]: design/high-level/Choices.md
 [FAQ]: design/high-level/FAQ.md
-[assembly-level explainer]: design/mvp/Explainer.md
+[AST explainer]: design/mvp/Explainer.md
+[async explainer]: design/mvp/Async.md
 [IDL]: design/mvp/WIT.md
 [binary format]: design/mvp/Binary.md
 [ABI]: design/mvp/CanonicalABI.md

design/mvp/Async.md

@@ -200,6 +200,7 @@ label'        ::= len:<u32> l:<label>                     => l    (if len = |l|)
 valtype       ::= i:<typeidx>                             => i
                 | pvt:<primvaltype>                       => pvt
 resourcetype  ::= 0x3f 0x7f f?:<funcidx>?                 => (resource (rep i32) (dtor f)?)
+                | 0x3e 0x7f f:<funcidx> cb?:<funcidx>?    => (resource (rep i32) (dtor async f (callback cb)?))
 functype      ::= 0x40 ps:<paramlist> rs:<resultlist>     => (func ps rs)
 paramlist     ::= lt*:vec(<labelvaltype>)                 => (param lt)*
 resultlist    ::= 0x00 t:<valtype>                        => (result t)
@@ -270,16 +271,24 @@ canon    ::= 0x00 0x00 f:<core:funcidx> opts:<opts> ft:<typeidx> => (canon lift
            | 0x01 0x00 f:<funcidx> opts:<opts>                   => (canon lower f opts (core func))
            | 0x02 rt:<typeidx>                                   => (canon resource.new rt (core func))
            | 0x03 rt:<typeidx>                                   => (canon resource.drop rt (core func))
+           | 0x07 rt:<typdidx>                                   => (canon resource.drop rt async (core func))
            | 0x04 rt:<typeidx>                                   => (canon resource.rep rt (core func))
            | 0x05 ft:<typeidx>                                   => (canon thread.spawn ft (core func))
            | 0x06                                                => (canon thread.hw_concurrency (core func))
+           | 0x08                                                => (canon task.start (core func))
+           | 0x09                                                => (canon task.return (core func))
+           | 0x0a                                                => (canon task.wait (core func))
+           | 0x0b                                                => (canon task.poll (core func))
+           | 0x0c                                                => (canon task.yield (core func))
 opts     ::= opt*:vec(<canonopt>)                                => opt*
 canonopt ::= 0x00                                                => string-encoding=utf8
            | 0x01                                                => string-encoding=utf16
            | 0x02                                                => string-encoding=latin1+utf16
            | 0x03 m:<core:memidx>                                => (memory m)
            | 0x04 f:<core:funcidx>                               => (realloc f)
            | 0x05 f:<core:funcidx>                               => (post-return f)
+           | 0x06                                                => async
+           | 0x07 f:<core:funcidx>                               => (callback f)
 ```
 Notes:
 * The second `0x00` byte in `canon` stands for the `func` sort and thus the