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Implement special-cased projection error message for some common traits

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This commit is contained in:
Michael Goulet 2022-07-03 20:17:08 +00:00
parent d394408fb3
commit 750f04d309
25 changed files with 80 additions and 43 deletions
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62
compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
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@ -1315,6 +1315,13 @@ trait InferCtxtPrivExt<'hir, 'tcx> {
error: &MismatchedProjectionTypes<'tcx>,
);
fn maybe_detailed_projection_msg(
&self,
pred: ty::ProjectionPredicate<'tcx>,
normalized_ty: ty::Term<'tcx>,
expected_ty: ty::Term<'tcx>,
) -> Option<String>;
fn fuzzy_match_tys(
&self,
a: Ty<'tcx>,
@ -1542,23 +1549,19 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
normalized_ty,
data.term,
) {
values = Some(infer::ValuePairs::Terms(ExpectedFound::new(
is_normalized_ty_expected,
normalized_ty,
data.term,
)));
values = Some((data, is_normalized_ty_expected, normalized_ty, data.term));
err_buf = error;
err = &err_buf;
}
}
let mut diag = struct_span_err!(
self.tcx.sess,
obligation.cause.span,
E0271,
"type mismatch resolving `{}`",
predicate
);
let msg = values
.and_then(|(predicate, _, normalized_ty, expected_ty)| {
self.maybe_detailed_projection_msg(predicate, normalized_ty, expected_ty)
})
.unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
let secondary_span = match predicate.kind().skip_binder() {
ty::PredicateKind::Projection(proj) => self
.tcx
@ -1596,7 +1599,13 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
&mut diag,
&obligation.cause,
secondary_span,
values,
values.map(|(_, is_normalized_ty_expected, normalized_ty, term)| {
infer::ValuePairs::Terms(ExpectedFound::new(
is_normalized_ty_expected,
normalized_ty,
term,
))
}),
err,
true,
false,
@ -1606,6 +1615,33 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
});
}
fn maybe_detailed_projection_msg(
&self,
pred: ty::ProjectionPredicate<'tcx>,
normalized_ty: ty::Term<'tcx>,
expected_ty: ty::Term<'tcx>,
) -> Option<String> {
let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
let self_ty = pred.projection_ty.self_ty();
if Some(pred.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output() {
Some(format!(
"expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it actually returns `{normalized_ty}`",
fn_kind = self_ty.prefix_string(self.tcx)
))
} else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
Some(format!(
"expected `{self_ty}` to be a future that yields `{expected_ty}`, but it actually yields `{normalized_ty}`"
))
} else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
Some(format!(
"expected `{self_ty}` to be an iterator of `{expected_ty}`, but it actually returns items of `{normalized_ty}`"
))
} else {
None
}
}
fn fuzzy_match_tys(
&self,
mut a: Ty<'tcx>,