Change heuristic and add tests

Author: estebank

Diff for: src/librustc_mir/borrow_check/diagnostics/mod.rs

@@ -776,13 +776,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             }
         }
 
-        let normal_ret = if let [ProjectionElem::Downcast(..), ProjectionElem::Field(_, _)] =
-            moved_place.projection
-        {
-            PatUse(stmt.source_info.span)
-        } else {
-            OtherUse(stmt.source_info.span)
-        };
+        let normal_ret =
+            if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
+                PatUse(stmt.source_info.span)
+            } else {
+                OtherUse(stmt.source_info.span)
+            };
 
         // We are trying to find MIR of the form:
         // ```

Diff for: src/test/ui/borrowck/move-in-pattern-mut.rs

@@ -0,0 +1,23 @@
+// Issue #63988
+#[derive(Debug)]
+struct S;
+fn foo(_: Option<S>) {}
+
+enum E {
+    V {
+        s: S,
+    }
+}
+fn bar(_: E) {}
+
+fn main() {
+    let s = Some(S);
+    if let Some(mut x) = s {
+        x = S;
+    }
+    foo(s); //~ ERROR use of moved value: `s`
+    let mut e = E::V { s: S };
+    let E::V { s: mut x } = e;
+    x = S;
+    bar(e); //~ ERROR use of moved value: `e`
+}

Diff for: src/test/ui/borrowck/move-in-pattern-mut.stderr

@@ -0,0 +1,33 @@
+error[E0382]: use of moved value: `s`
+  --> $DIR/move-in-pattern-mut.rs:18:9
+   |
+LL |     if let Some(mut x) = s {
+   |                 ----- value moved here
+...
+LL |     foo(s);
+   |         ^ value used here after partial move
+   |
+   = note: move occurs because value has type `S`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `s.0`
+   |
+LL |     if let Some(ref mut x) = s {
+   |                 ^^^
+
+error[E0382]: use of moved value: `e`
+  --> $DIR/move-in-pattern-mut.rs:22:9
+   |
+LL |     let E::V { s: mut x } = e;
+   |                   ----- value moved here
+LL |     x = S;
+LL |     bar(e);
+   |         ^ value used here after partial move
+   |
+   = note: move occurs because value has type `S`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `e.s`
+   |
+LL |     let E::V { s: ref mut x } = e;
+   |                   ^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0382`.

Diff for: src/test/ui/borrowck/move-in-pattern.fixed

@@ -4,10 +4,21 @@
 struct S;
 fn foo(_: Option<S>) {}
 
+enum E {
+    V {
+        s: S,
+    }
+}
+fn bar(_: E) {}
+
 fn main() {
     let s = Some(S);
     if let Some(ref x) = s {
         let _ = x;
     }
     foo(s); //~ ERROR use of moved value: `s`
+    let e = E::V { s: S };
+    let E::V { s: ref x } = e;
+    let _ = x;
+    bar(e); //~ ERROR use of moved value: `e`
 }

Diff for: src/test/ui/borrowck/move-in-pattern.rs

@@ -4,10 +4,21 @@
 struct S;
 fn foo(_: Option<S>) {}
 
+enum E {
+    V {
+        s: S,
+    }
+}
+fn bar(_: E) {}
+
 fn main() {
     let s = Some(S);
     if let Some(x) = s {
         let _ = x;
     }
     foo(s); //~ ERROR use of moved value: `s`
+    let e = E::V { s: S };
+    let E::V { s: x } = e;
+    let _ = x;
+    bar(e); //~ ERROR use of moved value: `e`
 }

Diff for: src/test/ui/borrowck/move-in-pattern.stderr

@@ -1,5 +1,5 @@
 error[E0382]: use of moved value: `s`
-  --> $DIR/move-in-pattern.rs:12:9
+  --> $DIR/move-in-pattern.rs:19:9
    |
 LL |     if let Some(x) = s {
    |                 - value moved here
@@ -13,6 +13,21 @@ help: borrow this field in the pattern to avoid moving `s.0`
 LL |     if let Some(ref x) = s {
    |                 ^^^
 
-error: aborting due to previous error
+error[E0382]: use of moved value: `e`
+  --> $DIR/move-in-pattern.rs:23:9
+   |
+LL |     let E::V { s: x } = e;
+   |                   - value moved here
+LL |     let _ = x;
+LL |     bar(e);
+   |         ^ value used here after partial move
+   |
+   = note: move occurs because value has type `S`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `e.s`
+   |
+LL |     let E::V { s: ref x } = e;
+   |                   ^^^
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0382`.

Diff for: src/test/ui/moves/moves-based-on-type-cyclic-types-issue-4821.stderr

@@ -8,6 +8,10 @@ LL |     consume(node) + r
    |             ^^^^ value used here after partial move
    |
    = note: move occurs because value has type `std::boxed::Box<List>`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `node.next.0`
+   |
+LL |         Some(ref right) => consume(right),
+   |              ^^^
 
 error: aborting due to previous error
 

Diff for: src/test/ui/pattern/bindings-after-at/borrowck-pat-by-move-and-ref-inverse.stderr

@@ -357,6 +357,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                   value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((ref mut b @ ref mut c, d @ ref e)) => {}
+   |                   ^^^
 
 error[E0382]: use of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:61:38
@@ -379,6 +383,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                                      value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((mut b @ ref mut c, ref d @ ref e)) => {}
+   |                                      ^^^
 
 error[E0382]: borrow of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:71:30
@@ -412,6 +420,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                   value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((ref mut b @ ref mut c, d @ ref e)) => {}
+   |                   ^^^
 
 error[E0382]: use of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:83:38
@@ -434,6 +446,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                                      value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((mut b @ ref mut c, ref d @ ref e)) => {}
+   |                                      ^^^
 
 error[E0382]: borrow of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:93:30

Diff for: src/test/ui/ref-suggestion.stderr

@@ -28,6 +28,10 @@ LL |     x;
    |     ^ value used here after partial move
    |
    = note: move occurs because value has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `x.0.0`
+   |
+LL |         (Some(ref y), ()) => {},
+   |               ^^^
 
 error: aborting due to 3 previous errors