Add canonical interface name

Author: lann

design/mvp/Explainer.md

@@ -33,6 +33,7 @@ more user-focused explanation, take a look at the
   * [Start definitions](#-start-definitions)
   * [Import and export definitions](#import-and-export-definitions)
     * [Name uniqueness](#name-uniqueness)
+    * [Canonical interface name](#canonical-interface-name)
 * [Component invariants](#component-invariants)
 * [JavaScript embedding](#JavaScript-embedding)
   * [JS API](#JS-API)
@@ -294,7 +295,7 @@ sort           ::= core <core:sort>
                  | type
                  | component
                  | instance
-inlineexport   ::= (export <exportname> <sortidx>)
+inlineexport   ::= (export "<exportname>" <versionsuffix>? <sortidx>)
 ```
 Because component-level function, type and instance definitions are different
 than core-level function, type and instance definitions, they are put into
@@ -574,8 +575,8 @@ instancedecl  ::= core-prefix(<core:type>)
                 | <alias>
                 | <exportdecl>
                 | <value> 🪙
-importdecl    ::= (import <importname> bind-id(<externdesc>))
-exportdecl    ::= (export <exportname> bind-id(<externdesc>))
+importdecl    ::= (import "<importname>" <versionsuffix>? bind-id(<externdesc>))
+exportdecl    ::= (export "<exportname>" <versionsuffix>? bind-id(<externdesc>))
 externdesc    ::= (<sort> (type <u32>) )
                 | core-prefix(<core:moduletype>)
                 | <functype>
@@ -2242,8 +2243,9 @@ the identifier `$x`). In the case of exports, the `<id>?` right after the
 preceding definition being exported (e.g., `(export $x "x" (func $f))` binds a
 new identifier `$x`).
 ```ebnf
-import ::= (import "<importname>" bind-id(<externdesc>))
-export ::= (export <id>? "<exportname>" <sortidx> <externdesc>?)
+import        ::= (import "<importname>" <versionsuffix>? bind-id(<externdesc>))
+export        ::= (export <id>? "<exportname>" <versionsuffix>? <sortidx> <externdesc>?)
+versionsuffix ::= (versionsuffix "<semver suffix>")
 ```
 All import names are required to be [strongly-unique]. Separately, all export
 names are also required to be [strongly-unique]. The rest of the grammar for
@@ -2276,17 +2278,23 @@ fragment      ::= <word>
                 | <acronym>
 word          ::= [a-z] [0-9a-z]*
 acronym       ::= [A-Z] [0-9A-Z]*
-interfacename ::= <namespace> <label> <projection> <version>?
-                | <namespace>+ <label> <projection>+ <version>? 🪺
+interfacename ::= <namespace> <label> <projection> <interfaceversion>?
+                | <namespace>+ <label> <projection>+ <interfaceversion>? 🪺
 namespace     ::= <words> ':'
 words         ::= <word>
                 | <words> '-' <word>
 projection    ::= '/' <label>
-version       ::= '@' <valid semver>
+# FIXME: surrounding alignment
+interfaceversion ::= '@' <valid semver>
+                   | '@' <canonversion>
+canonversion     ::= [1-9] [0-9]*
+                   | '0.' [1-9] [0-9]*
+                   | '0.0.' [1-9] [0-9]*
 depname       ::= 'unlocked-dep=<' <pkgnamequery> '>'
                 | 'locked-dep=<' <pkgname> '>' ( ',' <hashname> )?
 pkgnamequery  ::= <pkgpath> <verrange>?
-pkgname       ::= <pkgpath> <version>?
+pkgname       ::= <pkgpath> <pkgversion>?
+pkgversion    ::= '@' <valid semver>
 pkgpath       ::= <namespace> <words>
                 | <namespace>+ <words> <projection>* 🪺
 verrange      ::= '@*'
@@ -2539,6 +2547,42 @@ annotations. For example, the validation rules for `[constructor]foo` require
 for details.
 
 
+### Canonical Interface Name
+
+An `interfacename` (as defined above) is **canonical** iff it either:
+
+- has no `interfaceversion`
+- has an `interfaceversion` matching the `canonversion` production
+
+The purpose of `canonversion` is to simplify the matching of compatible import
+and export versions. For example, if a guest imports some interface from
+`wasi:http/[email protected]` and a host provides the (subtype-compatible) interface
+`wasi:http/[email protected]`, we'd like to make it easy for the host to link with the
+guest. The `canonversion` for both of these interfaces would be `0.2`, so this
+linking could be done by matching the interface names literally.
+
+A `valid semver` (as used in WIT) can be canonicalized by splitting it into two
+parts - the `canonversion` prefix and the remaining `semver suffix`. Using the
+`<major>.<minor>.<patch>` syntax of [Semantic Versioning 2.0]:
+
+- if `major` > 0, split immediately after `major`
+  - `1.2.3` &rarr; `1` / `.2.3`
+- otherwise if `minor` > 0, split immediately after `minor`
+  - `0.2.6-rc.1` &rarr; `0.2` / `.6-rc.1`
+- otherwise, split immediately after `patch`
+  - `0.0.1-alpha` &rarr; `0.0.1` / `-alpha`
+
+When component tooling canonicalizes a version, any `semver suffix` portion of the interface
+name removed should be preserved in imports / exports in the `versionsuffix`
+field. This gives component runtimes and other tools access to the original
+version for error messages, documentation, and other development purposes.
+
+For compatibility with older versions of this spec, non-canonical
+`interfacename`s (with `interfaceversion`s matching any `valid semver`) are
+temporarily permitted. These non-canonical names may trigger warnings and will
+start being rejected some time after after [WASI Preview 3] is released.
+
+
 ## Component Invariants
 
 As a consequence of the shared-nothing design described above, all calls into
@@ -2894,6 +2938,7 @@ For some use-case-focused, worked examples, see:
 [`rectype`]: https://webassembly.github.io/gc/core/text/types.html#text-rectype
 [shared-everything-threads]: https://github.com/WebAssembly/shared-everything-threads
 [WASI Preview 2]: https://github.com/WebAssembly/WASI/tree/main/wasip2#readme
+[WASI Preview 3]: https://github.com/WebAssembly/WASI/tree/main/wasip2#looking-forward-to-preview-3
 [reference types]: https://github.com/WebAssembly/reference-types/blob/master/proposals/reference-types/Overview.md
 
 [Strongly-unique]: #name-uniqueness