Auto merge of rust-lang#9093 - Jarcho:deref_ice, r=giraffate

Fix ICE in `dereference.rs`

fixes rust-lang#9089
changelog: Fix ICE when dereferencing or borrowing on explicit returns from closures

Author: bors

clippy_lints/src/dereference.rs

@@ -8,7 +8,7 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_ty, Visitor};
 use rustc_hir::{
-    self as hir, BindingAnnotation, Body, BodyId, BorrowKind, Expr, ExprKind, GenericArg, HirId, ImplItem,
+    self as hir, BindingAnnotation, Body, BodyId, BorrowKind, Expr, ExprKind, FnRetTy, GenericArg, HirId, ImplItem,
     ImplItemKind, Item, ItemKind, Local, MatchSource, Mutability, Node, Pat, PatKind, Path, QPath, TraitItem,
     TraitItemKind, TyKind, UnOp,
 };
@@ -717,18 +717,32 @@ fn walk_parents<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> (Position, &
 
             Node::Expr(parent) if parent.span.ctxt() == ctxt => match parent.kind {
                 ExprKind::Ret(_) => {
-                    let output = cx
-                        .tcx
-                        .fn_sig(cx.tcx.hir().body_owner_def_id(cx.enclosing_body.unwrap()))
-                        .skip_binder()
-                        .output();
-                    Some(if !output.is_ref() {
-                        Position::Other(precedence)
-                    } else if output.has_placeholders() || output.has_opaque_types() {
-                        Position::ReborrowStable(precedence)
-                    } else {
-                        Position::DerefStable(precedence)
-                    })
+                    let owner_id = cx.tcx.hir().body_owner(cx.enclosing_body.unwrap());
+                    Some(
+                        if let Node::Expr(Expr {
+                            kind: ExprKind::Closure { fn_decl, .. },
+                            ..
+                        }) = cx.tcx.hir().get(owner_id)
+                        {
+                            match fn_decl.output {
+                                FnRetTy::Return(ty) => binding_ty_auto_deref_stability(ty, precedence),
+                                FnRetTy::DefaultReturn(_) => Position::Other(precedence),
+                            }
+                        } else {
+                            let output = cx
+                                .tcx
+                                .fn_sig(cx.tcx.hir().local_def_id(owner_id))
+                                .skip_binder()
+                                .output();
+                            if !output.is_ref() {
+                                Position::Other(precedence)
+                            } else if output.has_placeholders() || output.has_opaque_types() {
+                                Position::ReborrowStable(precedence)
+                            } else {
+                                Position::DerefStable(precedence)
+                            }
+                        },
+                    )
                 },
                 ExprKind::Call(func, _) if func.hir_id == child_id => (child_id == e.hir_id).then(|| Position::Callee),
                 ExprKind::Call(func, args) => args

tests/ui/explicit_auto_deref.fixed

@@ -211,4 +211,8 @@ fn main() {
     unsafe {
         var(0, &**x);
     }
+
+    let s = &"str";
+    let _ = || return *s;
+    let _ = || -> &'static str { return s };
 }

tests/ui/explicit_auto_deref.rs

@@ -211,4 +211,8 @@ fn main() {
     unsafe {
         var(0, &**x);
     }
+
+    let s = &"str";
+    let _ = || return *s;
+    let _ = || -> &'static str { return *s };
 }

tests/ui/explicit_auto_deref.stderr

@@ -192,5 +192,11 @@ error: deref which would be done by auto-deref
 LL |     f_str(&&**ref_str); // `needless_borrow` will suggest removing only one reference
    |            ^^^^^^^^^^ help: try this: `ref_str`
 
-error: aborting due to 32 previous errors
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:217:41
+   |
+LL |     let _ = || -> &'static str { return *s };
+   |                                         ^^ help: try this: `s`
+
+error: aborting due to 33 previous errors