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Ensure the 0th slot of anyref table is undefined

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This is currently required by our ABI for wasm-bindgen where `None` js
values going out have an index of 0 and are intended to be `undefined`.
This also refactors initialization a bit to be slightly more generic
over the constants we already have defined in this module.
This commit is contained in:
Alex Crichton
2019-08-01 11:59:05 -07:00
parent 5aee2f9c6a
commit 6cc7e3dadf
1 changed files with 14 additions and 7 deletions
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21
crates/cli-support/src/js/mod.rs
View File

@ -2641,16 +2641,23 @@ impl<'a> Context<'a> {
Intrinsic::InitAnyrefTable => {
self.expose_anyref_table();
String::from(
// Grow the table to insert our initial values, and then also
// set the 0th slot to `undefined` since that's what we've
// historically used for our ABI which is that the index of 0
// returns `undefined` for types like `None` going out.
let mut base = format!(
"
const table = wasm.__wbg_anyref_table;
const offset = table.grow(4);
table.set(offset + 0, undefined);
table.set(offset + 1, null);
table.set(offset + 2, true);
table.set(offset + 3, false);
const offset = table.grow({});
table.set(0, undefined);
",
)
INITIAL_HEAP_VALUES.len(),
);
for (i, value) in INITIAL_HEAP_VALUES.iter().enumerate() {
base.push_str(&format!("table.set(offset + {}, {});\n", i, value));
}
base
}
};
Ok(expr)