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Rollup merge of #92381 - ThePuzzlemaker:issue-92308, r=estebank

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Suggest `return`ing tail expressions in async functions

This PR fixes #92308.

Previously, the suggestion to `return` tail expressions (introduced in #81769) did not apply to `async` functions, as the suggestion checked whether the types were equal disregarding `impl Future<Output = T>` syntax sugar for `async` functions. This PR changes that in order to fix a potential papercut.

I'm not sure if this is the "right" way to do this, so if there is a better way then please let me know.

I amended an existing test introduced in #81769 to add a regression test for this, if you think I should make a separate test I will.
This commit is contained in:
Matthias Krüger 2022-01-14 07:47:32 +01:00 • committed by GitHub
commit 347c744fe0
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3 changed files with 54 additions and 3 deletions
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13
compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
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@ -9,7 +9,7 @@ use rustc_hir as hir;
use rustc_hir::def::{CtorOf, DefKind};
use rustc_hir::lang_items::LangItem;
use rustc_hir::{Expr, ExprKind, ItemKind, Node, Path, QPath, Stmt, StmtKind, TyKind};
use rustc_infer::infer;
use rustc_infer::infer::{self, TyCtxtInferExt};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::{self, Binder, Ty};
use rustc_span::symbol::{kw, sym};
@ -608,6 +608,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
let bound_vars = self.tcx.late_bound_vars(fn_id);
let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
let ty = self.normalize_associated_types_in(expr.span, ty);
let ty = match self.tcx.asyncness(fn_id.owner) {
hir::IsAsync::Async => self.tcx.infer_ctxt().enter(|infcx| {
infcx.get_impl_future_output_ty(ty).unwrap_or_else(|| {
span_bug!(
fn_decl.output.span(),
"failed to get output type of async function"
)
})
}),
hir::IsAsync::NotAsync => ty,
};
if self.can_coerce(found, ty) {
err.multipart_suggestion(
"you might have meant to return this value",