bjoernager/rust
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Add more .await suggestions on E0308

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This commit is contained in:
Esteban Küber 2020-10-22 19:03:36 -07:00
parent 1829b4a887
commit c5485115dc
12 changed files with 171 additions and 192 deletions
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165
compiler/rustc_infer/src/infer/error_reporting/mod.rs
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@ -50,7 +50,6 @@ use super::region_constraints::GenericKind;
use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs};
use crate::infer;
use crate::infer::OriginalQueryValues;
use crate::traits::error_reporting::report_object_safety_error;
use crate::traits::{
IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
@ -65,7 +64,6 @@ use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_hir::{Item, ItemKind, Node};
use rustc_middle::ty::error::TypeError;
use rustc_middle::ty::ParamEnvAnd;
use rustc_middle::ty::{
self,
subst::{Subst, SubstsRef},
@ -1621,6 +1619,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
Mismatch::Variable(exp_found) => Some(exp_found),
Mismatch::Fixed(_) => None,
};
let exp_found = match terr {
// `terr` has more accurate type information than `exp_found` in match expressions.
ty::error::TypeError::Sorts(terr)
if exp_found.map_or(false, |ef| terr.found == ef.found) =>
{
Some(*terr)
}
_ => exp_found,
};
debug!("exp_found {:?} terr {:?}", exp_found, terr);
if let Some(exp_found) = exp_found {
self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
self.suggest_await_on_expect_found(cause, span, &exp_found, diag);
@ -1642,19 +1650,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
self.note_error_origin(diag, cause, exp_found);
}
fn suggest_await_on_expect_found(
&self,
cause: &ObligationCause<'tcx>,
exp_span: Span,
exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
diag: &mut DiagnosticBuilder<'tcx>,
) {
debug!(
"suggest_await_on_expect_found: exp_span={:?}, expected_ty={:?}, found_ty={:?}",
exp_span, exp_found.expected, exp_found.found
);
if let ty::Opaque(def_id, _) = *exp_found.expected.kind() {
fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
if let ty::Opaque(def_id, substs) = ty.kind() {
let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
// Future::Output
let item_def_id = self
@ -1665,37 +1662,121 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
.unwrap()
.def_id;
let projection_ty = self.tcx.projection_ty_from_predicates((def_id, item_def_id));
if let Some(projection_ty) = projection_ty {
let projection_query = self.canonicalize_query(
&ParamEnvAnd { param_env: self.tcx.param_env(def_id), value: projection_ty },
&mut OriginalQueryValues::default(),
);
if let Ok(resp) = self.tcx.normalize_projection_ty(projection_query) {
let normalized_ty = resp.value.value.normalized_ty;
debug!("suggest_await_on_expect_found: normalized={:?}", normalized_ty);
if ty::TyS::same_type(normalized_ty, exp_found.found) {
let span = if let ObligationCauseCode::Pattern {
span,
origin_expr: _,
root_ty: _,
} = cause.code
{
// scrutinee's span
span.unwrap_or(exp_span)
} else {
exp_span
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider awaiting on the future",
".await".to_string(),
Applicability::MaybeIncorrect,
);
let bounds = self.tcx.explicit_item_bounds(*def_id);
for (predicate, _) in bounds {
let predicate = predicate.subst(self.tcx, substs);
if let ty::PredicateAtom::Projection(projection_predicate) =
predicate.skip_binders()
{
if projection_predicate.projection_ty.item_def_id == item_def_id {
// We don't account for multiple `Future::Output = Ty` contraints.
return Some(projection_predicate.ty);
}
}
}
}
None
}
/// A possible error is to forget to add `.await` when using futures:
///
/// ```
/// async fn make_u32() -> u32 {
/// 22
/// }
///
/// fn take_u32(x: u32) {}
///
/// async fn foo() {
/// let x = make_u32();
/// take_u32(x);
/// }
/// ```
///
/// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
/// expected type. If this is the case, and we are inside of an async body, it suggests adding
/// `.await` to the tail of the expression.
fn suggest_await_on_expect_found(
&self,
cause: &ObligationCause<'tcx>,
exp_span: Span,
exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
diag: &mut DiagnosticBuilder<'tcx>,
) {
debug!(
"suggest_await_on_expect_found: exp_span={:?}, expected_ty={:?}, found_ty={:?}",
exp_span, exp_found.expected, exp_found.found,
);
if let ObligationCauseCode::CompareImplMethodObligation { .. } = &cause.code {
return;
}
match (
self.get_impl_future_output_ty(exp_found.expected),
self.get_impl_future_output_ty(exp_found.found),
) {
(Some(exp), Some(found)) if ty::TyS::same_type(exp, found) => match &cause.code {
ObligationCauseCode::IfExpression(box IfExpressionCause { then, .. }) => {
diag.multipart_suggestion(
"consider `await`ing on both `Future`s",
vec![
(then.shrink_to_hi(), ".await".to_string()),
(exp_span.shrink_to_hi(), ".await".to_string()),
],
Applicability::MaybeIncorrect,
);
}
ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
prior_arms,
..
}) => {
if let [.., arm_span] = &prior_arms[..] {
diag.multipart_suggestion(
"consider `await`ing on both `Future`s",
vec![
(arm_span.shrink_to_hi(), ".await".to_string()),
(exp_span.shrink_to_hi(), ".await".to_string()),
],
Applicability::MaybeIncorrect,
);
} else {
diag.help("consider `await`ing on both `Future`s");
}
}
_ => {
diag.help("consider `await`ing on both `Future`s");
}
},
(_, Some(ty)) if ty::TyS::same_type(exp_found.expected, ty) => {
let span = match cause.code {
// scrutinee's span
ObligationCauseCode::Pattern { span: Some(span), .. } => span,
_ => exp_span,
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
}
(Some(ty), _) if ty::TyS::same_type(ty, exp_found.found) => {
let span = match cause.code {
// scrutinee's span
ObligationCauseCode::Pattern { span: Some(span), .. } => span,
_ => exp_span,
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
}
_ => {}
}
}
/// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate,