Rollup merge of rust-lang#54825 - davidtwco:issue-52663-deref-raw-pointer, r=pnkfelix

NLL says "borrowed content" instead of more precise "dereference of raw pointer"

Part of rust-lang#52663.

Previously, move errors involving the dereference of a raw pointer would
say "borrowed content". This commit changes it to say "dereference of
raw pointer".

r? @nikomatsakis
cc @pnkfelix

Author: Mark-Simulacrum

src/librustc_mir/borrow_check/move_errors.rs

@@ -68,6 +68,7 @@ enum GroupedMoveError<'tcx> {
 enum BorrowedContentSource {
     Arc,
     Rc,
+    DerefRawPointer,
     Other,
 }
 
@@ -76,6 +77,7 @@ impl Display for BorrowedContentSource {
         match *self {
             BorrowedContentSource::Arc => write!(f, "an `Arc`"),
             BorrowedContentSource::Rc => write!(f, "an `Rc`"),
+            BorrowedContentSource::DerefRawPointer => write!(f, "dereference of raw pointer"),
             BorrowedContentSource::Other => write!(f, "borrowed content"),
         }
     }
@@ -279,6 +281,7 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                             self.prefixes(&original_path, PrefixSet::All)
                             .any(|p| p.is_upvar_field_projection(self.mir, &self.infcx.tcx)
                                  .is_some());
+                        debug!("report: ty={:?}", ty);
                         match ty.sty {
                             ty::Array(..) | ty::Slice(..) =>
                                 self.infcx.tcx.cannot_move_out_of_interior_noncopy(
@@ -582,6 +585,18 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
             }
         }
 
+        // If we didn't find an `Arc` or an `Rc`, then check specifically for
+        // a dereference of a place that has the type of a raw pointer.
+        // We can't use `place.ty(..).to_ty(..)` here as that strips away the raw pointer.
+        if let Place::Projection(box Projection {
+            base,
+            elem: ProjectionElem::Deref,
+        }) = place {
+            if base.ty(self.mir, self.infcx.tcx).to_ty(self.infcx.tcx).is_unsafe_ptr() {
+                return BorrowedContentSource::DerefRawPointer;
+            }
+        }
+
         BorrowedContentSource::Other
     }
 }

src/test/ui/borrowck/borrowck-move-from-unsafe-ptr.nll.stderr

@@ -1,10 +1,10 @@
-error[E0507]: cannot move out of borrowed content
+error[E0507]: cannot move out of dereference of raw pointer
   --> $DIR/borrowck-move-from-unsafe-ptr.rs:13:13
    |
 LL |     let y = *x; //~ ERROR cannot move out of dereference of raw pointer
    |             ^^
    |             |
-   |             cannot move out of borrowed content
+   |             cannot move out of dereference of raw pointer
    |             help: consider removing the `*`: `x`
 
 error: aborting due to previous error

src/test/ui/issues/issue-20801.nll.stderr

@@ -16,22 +16,22 @@ LL |     let b = unsafe { *imm_ref() };
    |                      cannot move out of borrowed content
    |                      help: consider removing the `*`: `imm_ref()`
 
-error[E0507]: cannot move out of borrowed content
+error[E0507]: cannot move out of dereference of raw pointer
   --> $DIR/issue-20801.rs:42:22
    |
 LL |     let c = unsafe { *mut_ptr() };
    |                      ^^^^^^^^^^
    |                      |
-   |                      cannot move out of borrowed content
+   |                      cannot move out of dereference of raw pointer
    |                      help: consider removing the `*`: `mut_ptr()`
 
-error[E0507]: cannot move out of borrowed content
+error[E0507]: cannot move out of dereference of raw pointer
   --> $DIR/issue-20801.rs:45:22
    |
 LL |     let d = unsafe { *const_ptr() };
    |                      ^^^^^^^^^^^^
    |                      |
-   |                      cannot move out of borrowed content
+   |                      cannot move out of dereference of raw pointer
    |                      help: consider removing the `*`: `const_ptr()`
 
 error: aborting due to 4 previous errors