Ignore ExprKind::DropTemps for some ref suggestions

Author: estebank

src/librustc/hir/mod.rs

@@ -1548,6 +1548,23 @@ impl Expr {
             }
         }
     }
+
+    /// If `Self.kind` is `ExprKind::DropTemps(expr)`, drill down until we get a non-`DropTemps`
+    /// `Expr`. This is used in suggestions to ignore this `ExprKind` as it is semantically
+    /// silent, only signaling the ownership system. By doing this, suggestions that check the
+    /// `ExprKind` of any given `Expr` for presentation don't have to care about `DropTemps`
+    /// beyond remembering to call this function before doing analysis on it.
+    pub fn peel_drop_temps(&self) -> &Self {
+        let mut base_expr = self;
+        loop {
+            match &base_expr.kind {
+                ExprKind::DropTemps(expr) => {
+                    base_expr = &expr;
+                }
+                _ => return base_expr,
+            }
+        }
+    }
 }
 
 impl fmt::Debug for Expr {

src/librustc_typeck/check/demand.rs

@@ -355,6 +355,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
         let is_macro = sp.from_expansion() && !is_desugaring;
 
+        // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
+        let expr = expr.peel_drop_temps();
+
         match (&expr.kind, &expected.kind, &checked_ty.kind) {
             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
                 (&ty::Str, &ty::Array(arr, _)) |

src/test/ui/if/if-no-match-bindings.stderr

@@ -2,10 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:18:8
    |
 LL |     if b_ref() {}
-   |        ^^^^^^^
-   |        |
-   |        expected bool, found &bool
-   |        help: consider dereferencing the borrow: `*b_ref()`
+   |        ^^^^^^^ expected bool, found &bool
    |
    = note: expected type `bool`
               found type `&bool`
@@ -14,10 +11,7 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:19:8
    |
 LL |     if b_mut_ref() {}
-   |        ^^^^^^^^^^^
-   |        |
-   |        expected bool, found &mut bool
-   |        help: consider dereferencing the borrow: `*b_mut_ref()`
+   |        ^^^^^^^^^^^ expected bool, found &mut bool
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -29,7 +23,7 @@ LL |     if &true {}
    |        ^^^^^
    |        |
    |        expected bool, found &bool
-   |        help: consider dereferencing the borrow: `*&true`
+   |        help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -41,7 +35,7 @@ LL |     if &mut true {}
    |        ^^^^^^^^^
    |        |
    |        expected bool, found &mut bool
-   |        help: consider dereferencing the borrow: `*&mut true`
+   |        help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -50,10 +44,7 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:24:11
    |
 LL |     while b_ref() {}
-   |           ^^^^^^^
-   |           |
-   |           expected bool, found &bool
-   |           help: consider dereferencing the borrow: `*b_ref()`
+   |           ^^^^^^^ expected bool, found &bool
    |
    = note: expected type `bool`
               found type `&bool`
@@ -62,10 +53,7 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:25:11
    |
 LL |     while b_mut_ref() {}
-   |           ^^^^^^^^^^^
-   |           |
-   |           expected bool, found &mut bool
-   |           help: consider dereferencing the borrow: `*b_mut_ref()`
+   |           ^^^^^^^^^^^ expected bool, found &mut bool
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -77,7 +65,7 @@ LL |     while &true {}
    |           ^^^^^
    |           |
    |           expected bool, found &bool
-   |           help: consider dereferencing the borrow: `*&true`
+   |           help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -89,7 +77,7 @@ LL |     while &mut true {}
    |           ^^^^^^^^^
    |           |
    |           expected bool, found &mut bool
-   |           help: consider dereferencing the borrow: `*&mut true`
+   |           help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&mut bool`

src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr

@@ -520,7 +520,7 @@ LL |     if &let 0 = 0 {}
    |        ^^^^^^^^^^
    |        |
    |        expected bool, found &bool
-   |        help: consider dereferencing the borrow: `*&let 0 = 0`
+   |        help: consider removing the borrow: `let 0 = 0`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -708,7 +708,7 @@ LL |     while &let 0 = 0 {}
    |           ^^^^^^^^^^
    |           |
    |           expected bool, found &bool
-   |           help: consider dereferencing the borrow: `*&let 0 = 0`
+   |           help: consider removing the borrow: `let 0 = 0`
    |
    = note: expected type `bool`
               found type `&bool`