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Get rid of the wasm interface types return pointer hacks

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Now that using standard Wasm interface types implies multi-value support, we
don't need these return pointer hacks anymore.
This commit is contained in:
Nick Fitzgerald
2019-10-03 13:24:50 -07:00
parent 311ae1941f
commit 25dd84c503
2 changed files with 22 additions and 95 deletions
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62
crates/cli-support/src/webidl/standard.rs
View File

@ -16,39 +16,6 @@
//! generating any JS glue. Any JS glue currently generated is also invalid if
//! the module contains the wasm bindings section and it's actually respected.
// NB: Returning strings is weird
//
// This module has what is currently a pretty gross hack for dealing with
// returning strings. One of the banner features of WebIDL bindings is not
// requiring any language-specific glue to use wasm files and you get all sorts
// of types like integers and strings by default. Note that strings are a huge
// thing here.
//
// Dealing with *incoming* strings is easy enough in that the binding expression
// has an allocator function to call and it's filled in and passed as two
// pointers. Outgoing strings are a little harder, however, for two reasons:
//
// * One is that we need to return two values, which requires multi-value
// * Another is that someone's got to free the string at some point
//
// Rust/wasm-bindgen don't support multi-value, and WebIDL bindings as literally
// spec'd right this red hot second don't support freeing strings that we pass
// out. These both have obvious fixes (supporting multi-value and extending the
// bindings spec to support freeing) but we also want something working right
// this red-hot second.
//
// To get things working we employ a terrible hack where the first bindign
// expression of the result a function may indicate "use a thing that's way off
// in the ether" and that's actually a sentinel for "oh ignore everything else
// and the string is returned through an out-ptr as the first argument". This
// manifests in all sorts of special hacks all over the place to handle this,
// and it's a real bummer.
//
// This is in general just an explainer for the current state of things and
// also a preemptive apology for writing the code to handle this in so many
// places. I, like you, look forward to actually fixing this for real as the
// spec continues to evolve and we implement more in wasm-bindgen.
use crate::descriptor::VectorKind;
use crate::webidl::{AuxExportKind, AuxImport, AuxValue, JsImport, JsImportName};
use crate::webidl::{NonstandardIncoming, NonstandardOutgoing};
@ -240,7 +207,7 @@ pub fn add_section(
name
)
})?;
let mut result = extract_outgoing(&binding.outgoing).with_context(|_| {
let result = extract_outgoing(&binding.outgoing).with_context(|_| {
format!(
"failed to map return value for export `{}` to standard \
binding expressions",
@ -248,18 +215,7 @@ pub fn add_section(
)
})?;
// see comment at top of this module about returning strings for what
// this is doing and why it's weird
if binding.return_via_outptr.is_some() {
result.insert(
0,
ast::OutgoingBindingExpressionAs {
idx: u32::max_value(),
ty: ast::WebidlScalarType::Long.into(),
}
.into(),
);
}
assert!(binding.return_via_outptr.is_none());
let binding = section.bindings.insert(ast::ExportBinding {
wasm_ty: binding.wasm_ty,
webidl_ty: copy_ty(
@ -293,24 +249,14 @@ pub fn add_section(
module_name, name,
)
})?;
let mut result = extract_incoming(&binding.incoming).with_context(|_| {
let result = extract_incoming(&binding.incoming).with_context(|_| {
format!(
"failed to map return value of import `{}::{}` to standard \
binding expressions",
module_name, name,
)
})?;
// see comment at top of this module about returning strings for what
// this is doing and why it's weird
if binding.return_via_outptr.is_some() {
result.insert(
0,
ast::IncomingBindingExpressionGet {
idx: u32::max_value(),
}
.into(),
);
}
assert!(binding.return_via_outptr.is_none());
let binding = section.bindings.insert(ast::ImportBinding {
wasm_ty: binding.wasm_ty,
webidl_ty: copy_ty(