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Make the error message better
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16cbdd0321
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@ -206,6 +206,9 @@ hir_analysis_manual_implementation =
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.label = manual implementations of `{$trait_name}` are experimental
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.help = add `#![feature(unboxed_closures)]` to the crate attributes to enable
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hir_analysis_method_should_return_future = method should be `async` or return a future, but it is synchronous
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.note = this method is `async` so it expects a future to be returned
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hir_analysis_missing_one_of_trait_item = not all trait items implemented, missing one of: `{$missing_items_msg}`
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.label = missing one of `{$missing_items_msg}` in implementation
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.note = required because of this annotation
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@ -1,5 +1,5 @@
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use super::potentially_plural_count;
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use crate::errors::LifetimesOrBoundsMismatchOnTrait;
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use crate::errors::{LifetimesOrBoundsMismatchOnTrait, MethodShouldReturnFuture};
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use hir::def_id::{DefId, DefIdMap, LocalDefId};
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use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
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use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, ErrorGuaranteed};
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@ -10,7 +10,7 @@ use rustc_hir::{GenericParamKind, ImplItemKind};
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use rustc_infer::infer::outlives::env::OutlivesEnvironment;
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use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
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use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
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use rustc_infer::traits::util;
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use rustc_infer::traits::{util, FulfillmentError};
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use rustc_middle::ty::error::{ExpectedFound, TypeError};
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use rustc_middle::ty::fold::BottomUpFolder;
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use rustc_middle::ty::util::ExplicitSelf;
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@ -664,8 +664,13 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
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// RPITs.
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let errors = ocx.select_all_or_error();
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if !errors.is_empty() {
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let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
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return Err(reported);
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if let Err(guar) = try_report_async_mismatch(tcx, infcx, &errors, trait_m, impl_m, impl_sig)
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{
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return Err(guar);
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}
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let guar = infcx.err_ctxt().report_fulfillment_errors(errors);
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return Err(guar);
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}
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// Finally, resolve all regions. This catches wily misuses of
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@ -2217,3 +2222,47 @@ fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
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ty::AssocKind::Type => "type",
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}
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}
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/// Manually check here that `async fn foo()` wasn't matched against `fn foo()`,
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/// and extract a better error if so.
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fn try_report_async_mismatch<'tcx>(
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tcx: TyCtxt<'tcx>,
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infcx: &InferCtxt<'tcx>,
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errors: &[FulfillmentError<'tcx>],
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trait_m: ty::AssocItem,
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impl_m: ty::AssocItem,
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impl_sig: ty::FnSig<'tcx>,
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) -> Result<(), ErrorGuaranteed> {
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if !tcx.asyncness(trait_m.def_id).is_async() {
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return Ok(());
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}
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let ty::Alias(ty::Projection, ty::AliasTy { def_id: async_future_def_id, .. }) =
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*tcx.fn_sig(trait_m.def_id).skip_binder().skip_binder().output().kind()
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else {
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bug!("expected `async fn` to return an RPITIT");
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};
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for error in errors {
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if let traits::BindingObligation(def_id, _) = *error.root_obligation.cause.code()
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&& def_id == async_future_def_id
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&& let Some(proj) = error.root_obligation.predicate.to_opt_poly_projection_pred()
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&& let Some(proj) = proj.no_bound_vars()
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&& infcx.can_eq(
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error.root_obligation.param_env,
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proj.term.ty().unwrap(),
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impl_sig.output(),
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)
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{
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// FIXME: We should suggest making the fn `async`, but extracting
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// the right span is a bit difficult.
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return Err(tcx.sess.dcx().emit_err(MethodShouldReturnFuture {
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span: tcx.def_span(impl_m.def_id),
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method_name: trait_m.name,
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trait_item_span: tcx.hir().span_if_local(trait_m.def_id),
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}));
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}
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}
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Ok(())
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}
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@ -1501,6 +1501,16 @@ pub struct NotSupportedDelegation<'a> {
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pub callee_span: Span,
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}
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#[derive(Diagnostic)]
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#[diag(hir_analysis_method_should_return_future)]
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pub struct MethodShouldReturnFuture {
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#[primary_span]
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pub span: Span,
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pub method_name: Symbol,
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#[note]
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pub trait_item_span: Option<Span>,
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}
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#[derive(Diagnostic)]
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#[diag(hir_analysis_unused_generic_parameter)]
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pub(crate) struct UnusedGenericParameter {
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@ -8,7 +8,7 @@ trait MyTrait {
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impl MyTrait for i32 {
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fn foo(&self) -> i32 {
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//~^ ERROR: `i32` is not a future
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//~^ ERROR: method should be `async` or return a future, but it is synchronous
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*self
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}
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}
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@ -1,17 +1,14 @@
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error[E0277]: `i32` is not a future
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--> $DIR/fn-not-async-err.rs:10:22
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error: method should be `async` or return a future, but it is synchronous
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--> $DIR/fn-not-async-err.rs:10:5
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LL | fn foo(&self) -> i32 {
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| ^^^ `i32` is not a future
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| ^^^^^^^^^^^^^^^^^^^^
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= help: the trait `Future` is not implemented for `i32`
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= note: i32 must be a future or must implement `IntoFuture` to be awaited
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note: required by a bound in `MyTrait::{opaque#0}`
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note: this method is `async` so it expects a future to be returned
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--> $DIR/fn-not-async-err.rs:6:5
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LL | async fn foo(&self) -> i32;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `MyTrait::{opaque#0}`
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 1 previous error
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For more information about this error, try `rustc --explain E0277`.
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