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Adjust binary encoding of import/export names #623

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28 changes: 16 additions & 12 deletions design/mvp/Binary.md
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Original file line number Diff line number Diff line change
Expand Up @@ -228,8 +228,8 @@ instancedecl ::= 0x00 t:<core:type> => t
| 0x01 t:<type> => t
| 0x02 a:<alias> => a
| 0x04 ed:<exportdecl> => ed
importdecl ::= in:<importname'> ed:<externdesc> => (import in ed)
exportdecl ::= en:<exportname'> ed:<externdesc> => (export en ed)
importdecl ::= in:<importname> ed:<externdesc> => (import in ed)
exportdecl ::= en:<exportname> ed:<externdesc> => (export en ed)
externdesc ::= 0x00 0x11 i:<core:typeidx> => (core module (type i))
| 0x01 i:<typeidx> => (func (type i))
| 0x02 b:<valuebound> => (value b) 🪙
Expand Down Expand Up @@ -386,13 +386,15 @@ flags are set.
(See [Import and Export Definitions](Explainer.md#import-and-export-definitions)
in the explainer.)
```ebnf
import ::= in:<importname'> ed:<externdesc> => (import in ed)
export ::= en:<exportname'> si:<sortidx> ed?:<externdesc>? => (export en si ed?)
importname' ::= 0x00 len:<u32> in:<importname> => in (if len = |in|)
| 0x01 len:<u32> in:<importname> vs:<versionsuffix'> => in vs (if len = |in|) 🔗
exportname' ::= 0x00 len:<u32> en:<exportname> => en (if len = |en|)
| 0x01 len:<u32> en:<exportname> vs:<versionsuffix'> => in vs (if len = |in|) 🔗
versionsuffix' ::= len:<u32> vs:<semversuffix> => (versionsuffix vs) (if len = |vs|) 🔗
import ::= in:<importname> ed:<externdesc> => (import in ed)
export ::= en:<exportname> si:<sortidx> ed?:<externdesc>? => (export en si ed?)
importname ::= 0x00 len:<u32> in:<importname> => in (if len = |in|)
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@lukewagner lukewagner Mar 23, 2026

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The goal of importname'/exportname' was avoid the confusion in this line, which otherwise looks recursive. One alternative idea is to say <text:importname> (and then update the bullet below which establishes the link of importname to the text format).

| 0x01 len:<u32> in:<importname> => in (if len = |in|)
| 0x02 len:<u32> in:<importname> vs:<versionsuffix> => in vs (if len = |in|) 🔗
exoprtname ::= 0x00 len:<u32> in:<exoprtname> => in (if len = |in|)
| 0x01 len:<u32> in:<exoprtname> => in (if len = |in|)
| 0x02 len:<u32> in:<exoprtname> vs:<versionsuffix> => in vs (if len = |in|) 🔗
Comment on lines +394 to +396
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@lukewagner lukewagner Mar 23, 2026

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Suggested change
exoprtname ::= 0x00 len:<u32> in:<exoprtname> => in (if len = |in|)
| 0x01 len:<u32> in:<exoprtname> => in (if len = |in|)
| 0x02 len:<u32> in:<exoprtname> vs:<versionsuffix> => in vs (if len = |in|) 🔗
exportname ::= 0x00 len:<u32> in:<exportname> => in (if len = |in|)
| 0x01 len:<u32> in:<exportname> => in (if len = |in|)
| 0x02 len:<u32> in:<exportname> vs:<versionsuffix> => in vs (if len = |in|) 🔗

versionsuffix ::= len:<u32> vs:<semversuffix> => (versionsuffix vs) (if len = |vs|) 🔗
```

Notes:
Expand All @@ -406,6 +408,8 @@ Notes:
of the inferred `externdesc` of the `sortidx`.
* `<importname>` and `<exportname>` refer to the productions defined in the
[text format](Explainer.md#import-and-export-definitions).
* `<importname>` and `<exportname>` will [be cleaned up for a 1.0
release](##binary-format-warts-to-fix-in-a-10-release).
* The `<importname>`s of a component must all be [strongly-unique]. Separately,
the `<exportname>`s of a component must also all be [strongly-unique].
* Validation requires that annotated `plainname`s only occur on `func` imports
Expand Down Expand Up @@ -519,9 +523,9 @@ named once.
* The two `depname` cases should be merged into one (`dep=<...>`)
* The two `list` type codes should be merged into one with an optional immediate
and similarly for `func`.
* The `0x00` variant of `importname'` and `exportname'` will be removed. Any
remaining variant(s) will be renumbered or the prefix byte will be removed or
repurposed.
* The `0x00` and `0x01` variant of `importname` and `exportname` will be
removed. Any remaining variant(s) will be renumbered or the prefix byte will
be removed or repurposed.
* Most built-ins should have a `<canonopt>*` immediate instead of an ad hoc
subset of `canonopt`s.
* Add optional `shared` immediate to all canonical definitions (explicitly or
Expand Down
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