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Auto merge of #87033 - FabianWolff:issue-87017, r=estebank

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Provide a suggestion when trying to destructure a `Vec` as a slice

Fixes #87017.

r? `@estebank`
This commit is contained in:
bors 2021-08-03 08:00:30 +00:00
commit 3354a44d2f
5 changed files with 110 additions and 2 deletions
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18
compiler/rustc_typeck/src/check/pat.rs
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@ -16,6 +16,7 @@ use rustc_span::lev_distance::find_best_match_for_name;
use rustc_span::source_map::{Span, Spanned};
use rustc_span::symbol::Ident;
use rustc_span::{BytePos, DUMMY_SP};
use rustc_trait_selection::autoderef::Autoderef;
use rustc_trait_selection::traits::{ObligationCause, Pattern};
use ty::VariantDef;
@ -1769,7 +1770,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// The expected type must be an array or slice, but was neither, so error.
_ => {
if !expected.references_error() {
self.error_expected_array_or_slice(span, expected);
self.error_expected_array_or_slice(span, expected, ti);
}
let err = self.tcx.ty_error();
(err, Some(err), err)
@ -1882,7 +1883,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
.emit();
}
fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>) {
fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
let mut err = struct_span_err!(
self.tcx.sess,
span,
@ -1894,6 +1895,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
if let ty::Array(..) | ty::Slice(..) = ty.kind() {
err.help("the semantics of slice patterns changed recently; see issue #62254");
}
} else if Autoderef::new(&self.infcx, self.param_env, self.body_id, span, expected_ty, span)
.any(|(ty, _)| matches!(ty.kind(), ty::Slice(..)))
{
if let (Some(span), true) = (ti.span, ti.origin_expr) {
if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
err.span_suggestion(
span,
"consider slicing here",
format!("{}[..]", snippet),
Applicability::MachineApplicable,
);
}
}
}
err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));
err.emit();