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Auto merge of #12982 - jridgewell:into_future, r=Veykril

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Implement IntoFuture type inference

One of my projects is using [IntoFuture](https://doc.rust-lang.org/std/future/trait.IntoFuture.html) to make our async code a little less verbose. However, rust-analyzer can't infer the output type of an await expression if the value uses `IntoFuture` to convert into another type. So we're getting `{unknown}` types everywhere since switching.

`foo.await` itself [desugars](e4417cf020/compiler/rustc_ast_lowering/src/expr.rs (L644-L658)) into a `match into_future(foo) {}`, with every `Future` impl getting a [default](e4417cf020/library/core/src/future/into_future.rs (L131-L139)) `IntoFuture` implementation. I'm not sure if we want to disable the old `future_trait` paths, since this only recently [stabilize](https://github.com/rust-lang/rust/pull/98718).
This commit is contained in:
bors 2022-08-18 07:37:47 +00:00
commit 1da9156b0d
11 changed files with 178 additions and 35 deletions
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32
crates/hir/src/source_analyzer.rs
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@ -27,6 +27,7 @@ use hir_def::{
use hir_expand::{
builtin_fn_macro::BuiltinFnLikeExpander,
hygiene::Hygiene,
mod_path::path,
name,
name::{AsName, Name},
HirFileId, InFile,
@ -269,14 +270,35 @@ impl SourceAnalyzer {
db: &dyn HirDatabase,
await_expr: &ast::AwaitExpr,
) -> Option<FunctionId> {
let ty = self.ty_of_expr(db, &await_expr.expr()?.into())?;
let mut ty = self.ty_of_expr(db, &await_expr.expr()?.into())?.clone();
let op_fn = db
let into_future_trait = self
.resolver
.resolve_known_trait(db.upcast(), &path![core::future::IntoFuture])
.map(Trait::from);
if let Some(into_future_trait) = into_future_trait {
let type_ = Type::new_with_resolver(db, &self.resolver, ty.clone());
if type_.impls_trait(db, into_future_trait, &[]) {
let items = into_future_trait.items(db);
let into_future_type = items.into_iter().find_map(|item| match item {
AssocItem::TypeAlias(alias)
if alias.name(db) == hir_expand::name![IntoFuture] =>
{
Some(alias)
}
_ => None,
})?;
let future_trait = type_.normalize_trait_assoc_type(db, &[], into_future_type)?;
ty = future_trait.ty;
}
}
let poll_fn = db
.lang_item(self.resolver.krate(), hir_expand::name![poll].to_smol_str())?
.as_function()?;
let substs = hir_ty::TyBuilder::subst_for_def(db, op_fn).push(ty.clone()).build();
Some(self.resolve_impl_method_or_trait_def(db, op_fn, &substs))
let substs = hir_ty::TyBuilder::subst_for_def(db, poll_fn).push(ty.clone()).build();
Some(self.resolve_impl_method_or_trait_def(db, poll_fn, &substs))
}
pub(crate) fn resolve_prefix_expr(