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Support Option with custom enums in JS

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Find a hole automatically to use a sentinel value for `None`, and then
just wire everything up!

Closes #1198
This commit is contained in:
Alex Crichton
2019-01-28 14:12:02 -08:00
parent 03e52c7045
commit 9224455077
8 changed files with 119 additions and 5 deletions
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34
crates/macro-support/src/parser.rs
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@ -953,6 +953,12 @@ impl MacroParse<()> for syn::ItemEnum {
_ => bail_span!(self, "only public enums are allowed with #[wasm_bindgen]"),
}
if self.variants.len() == 0 {
bail_span!(self, "cannot export empty enums to JS");
}
let has_discriminant = self.variants[0].discriminant.is_some();
let variants = self
.variants
.iter()
@ -962,6 +968,14 @@ impl MacroParse<()> for syn::ItemEnum {
syn::Fields::Unit => (),
_ => bail_span!(v.fields, "only C-Style enums allowed with #[wasm_bindgen]"),
}
// Require that everything either has a discriminant or doesn't.
// We don't really want to get in the business of emulating how
// rustc assigns values to enums.
if v.discriminant.is_some() != has_discriminant {
bail_span!(v, "must either annotate discriminant of all variants or none");
}
let value = match v.discriminant {
Some((
_,
@ -992,12 +1006,30 @@ impl MacroParse<()> for syn::ItemEnum {
value,
})
})
.collect::<Result<_, Diagnostic>>()?;
.collect::<Result<Vec<_>, Diagnostic>>()?;
let mut values = variants.iter().map(|v| v.value).collect::<Vec<_>>();
values.sort();
let hole = values.windows(2)
.filter_map(|window| {
if window[0] + 1 != window[1] {
Some(window[0] + 1)
} else {
None
}
})
.next()
.unwrap_or(*values.last().unwrap() + 1);
for value in values {
assert!(hole != value);
}
let comments = extract_doc_comments(&self.attrs);
program.enums.push(ast::Enum {
name: self.ident,
variants,
comments,
hole,
});
Ok(())
}