Do not error on let ref x: str = *"";

Author: estebank

compiler/rustc_hir_typeck/src/gather_locals.rs

@@ -105,24 +105,41 @@ impl<'a, 'tcx> GatherLocalsVisitor<'a, 'tcx> {
  .insert(hir_ty.hir_id, c_ty);
 
  let ty = o_ty.normalized;
- if let hir::PatKind::Wild = decl.pat.kind {
- // We explicitly allow `let _: dyn Trait;` (!)
- } else {
- if self.outermost_fn_param_pat.is_some() {
- if !self.fcx.tcx.features().unsized_fn_params {
- self.fcx.require_type_is_sized(
- ty,
- hir_ty.span,
- traits::SizedArgumentType(Some(decl.pat.hir_id)),
- );
- }
- } else {
- if !self.fcx.tcx.features().unsized_locals {
- self.fcx.require_type_is_sized(
- ty,
- hir_ty.span,
- traits::VariableType(decl.pat.hir_id),
- );
+ match decl.pat.kind {
+ // We explicitly allow `let ref x: str = *"";`
+ hir::PatKind::Binding(hir::BindingAnnotation(hir::ByRef::Yes(_), _), ..) => {}
+ // We explicitly allow `let _: dyn Trait;` and allow the `visit_pat` check to
+ // handle `let (x, _): (sized, str) = *r;`. Otherwise with the later we'd
+ // complain incorrectly about the `str` that is otherwise unused.
+ _ if {
+ let mut is_wild = false;
+ decl.pat.walk(|pat| {
+ if let hir::PatKind::Wild = pat.kind {
+ is_wild = true;
+ false
+ } else {
+ true
+ }
+ });
+ is_wild
+ } => {}
+ _ => {
+ if self.outermost_fn_param_pat.is_some() {
+ if !self.fcx.tcx.features().unsized_fn_params {
+ self.fcx.require_type_is_sized(
+ ty,
+ hir_ty.span,
+ traits::SizedArgumentType(Some(decl.pat.hir_id)),
+ );
+ }
+ } else {
+ if !self.fcx.tcx.features().unsized_locals {
+ self.fcx.require_type_is_sized(
+ ty,
+ hir_ty.span,
+ traits::VariableType(decl.pat.hir_id),
+ );
+ }
  }
  }
  }

tests/ui/sized/let-ref-pat-unsized-works.rs

@@ -0,0 +1,11 @@
+//@ build-pass
+#![allow(unused)]
+
+fn main() {
+ let ref x: str = *"";
+}
+
+fn foo(r: &(usize, str)) -> usize {
+ let (x, _): (usize, str) = *r;
+ x
+}