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Split 'use' inside worlds into 'use import' and 'use export' #308

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Split 'use' inside worlds into 'use import' and 'use export' #308

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a4dcbe8
Split 'use' inside worlds into 'use import' and 'use export'
lukewagner Feb 23, 2024
63ad7c1
Add optional 'using' clause to world imports and exports
lukewagner Jul 11, 2024
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68 changes: 57 additions & 11 deletions design/mvp/WIT.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1051,23 +1051,75 @@ world-items ::= gate world-definition

world-definition ::= export-item
| import-item
| use-item
| world-use-item
| typedef-item
| include-item

export-item ::= 'export' id ':' extern-type
| 'export' use-path ';'
| 'export' use-path using-clause? ';'
import-item ::= 'import' id ':' extern-type
| 'import' use-path ';'
| 'import' use-path using-clause? ';'

extern-type ::= func-type ';' | 'interface' '{' interface-items* '}'
extern-type ::= func-type ';' | 'interface' '{' interface-items* '}' using-clause?

using-clause ::= 'using' '{' using-item (',' using-item)* '}'
using-item ::= use-path '=' world-use-path
world-use-path ::= 'import' use-path
| 'export' use-path

world-use-item ::= 'use' world-use-path use-projection ';'
use-projection ::= '.' '{' projection-item (',' projection-item)* '}'
projection-item ::= id
| id 'as' id
```

Note that worlds can import types and define their own types to be exported
from the root of a component and used within functions imported and exported.
The `interface` item here additionally defines the grammar for IDs used to refer
to `interface` items.

The `use` items work just like `use` inside an `interface` except that they can
explicitly prefix the `use-path` with `export` or `import`, allowing a world
to import and export the same interface and independently refer to both. An
unqualified `use-path` may not be used if `use-path` is both imported and
exported. For example:
```wit
interface i {
resource r;
}

world w {
import i;
export i;
use import i.{r as r1};
use export i.{r as r2};
export transform: func(in: r1) -> r2;
}
```

A `using` clause may be added after imports or exports of interfaces to
override the default type-sharing behavior within the imported `interface` and
all `interface`s transitively `use`d by it. For example:
```wit
interface blob-store {
resource blob { ... }
}

interface blob-transform {
use blob-store.{blob};
transform: func(in: blob) -> blob;
}

interface compressed-blob-store {
resource blob { ... }
}

world w {
import compressed-blob-store;
export blob-transform using { blob-store = import compressed-blob-store };
}
```

[`componenttype`]: Explainer.md#type-definitions

## Item: `include`
Expand Down Expand Up @@ -1144,13 +1196,7 @@ use my:dependency/the-interface.{more, names as foo}
Specifically the structure of this is:

```ebnf
use-item ::= 'use' use-path '.' '{' use-names-list '}' ';'

use-names-list ::= use-names-item
| use-names-item ',' use-names-list?

use-names-item ::= id
| id 'as' id
use-item ::= 'use' use-path use-projection ';'
```

Note: Here `use-names-list?` means at least one `use-name-list` term.
Expand Down
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