Account for dereference expressions

Author: estebank

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -410,13 +410,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
     fn add_move_hints(&self, error: GroupedMoveError<'tcx>, err: &mut Diagnostic, span: Span) {
         match error {
             GroupedMoveError::MovesFromPlace { mut binds_to, move_from, .. } => {
-                err.span_suggestion_verbose(
-                    span.shrink_to_lo(),
-                    "consider borrowing here",
-                    "&".to_string(),
-                    Applicability::Unspecified,
-                );
-
+                self.add_borrow_suggestions(err, span);
                 if binds_to.is_empty() {
                     let place_ty = move_from.ty(self.body, self.infcx.tcx).ty;
                     let place_desc = match self.describe_place(move_from.as_ref()) {
@@ -459,6 +453,27 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         }
     }
 
+    fn add_borrow_suggestions(&self, err: &mut Diagnostic, span: Span) {
+        match self.infcx.tcx.sess.source_map().span_to_snippet(span) {
+            Ok(snippet) if snippet.starts_with('*') => {
+                err.span_suggestion_verbose(
+                    span.with_hi(span.lo() + BytePos(1)),
+                    "consider removing the dereference here",
+                    String::new(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            _ => {
+                err.span_suggestion_verbose(
+                    span.shrink_to_lo(),
+                    "consider borrowing here",
+                    "&".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+        }
+    }
+
     fn add_move_error_suggestions(&self, err: &mut Diagnostic, binds_to: &[Local]) {
         let mut suggestions: Vec<(Span, String, String)> = Vec::new();
         for local in binds_to {

src/test/ui/borrowck/access-mode-in-closures.stderr

@@ -7,10 +7,11 @@ LL |         match *s { S(v) => v }
    |                      data moved here
    |                      move occurs because `v` has type `Vec<isize>`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -         match *s { S(v) => v }
+LL +         match s { S(v) => v }
    |
-LL |         match &*s { S(v) => v }
-   |               +
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-issue-2657-2.fixed

@@ -0,0 +1,12 @@
+// run-rustfix
+fn main() {
+
+    let x: Option<Box<_>> = Some(Box::new(1));
+
+    match x {
+      Some(ref y) => {
+        let _b = y; //~ ERROR cannot move out
+      }
+      _ => {}
+    }
+}

src/test/ui/borrowck/borrowck-issue-2657-2.rs

@@ -1,3 +1,4 @@
+// run-rustfix
 fn main() {
 
     let x: Option<Box<_>> = Some(Box::new(1));

src/test/ui/borrowck/borrowck-issue-2657-2.stderr

@@ -1,13 +1,14 @@
 error[E0507]: cannot move out of `*y` which is behind a shared reference
-  --> $DIR/borrowck-issue-2657-2.rs:7:18
+  --> $DIR/borrowck-issue-2657-2.rs:8:18
    |
 LL |         let _b = *y;
    |                  ^^ move occurs because `*y` has type `Box<i32>`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -         let _b = *y;
+LL +         let _b = y;
    |
-LL |         let _b = &*y;
-   |                  +
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-move-error-with-note.fixed

@@ -10,7 +10,7 @@ enum Foo {
 
 fn blah() {
     let f = &Foo::Foo1(Box::new(1), Box::new(2));
-    match &*f { //~ ERROR cannot move out of
+    match f { //~ ERROR cannot move out of
         Foo::Foo1(num1,
                   num2) => (),
         Foo::Foo2(num) => (),

src/test/ui/borrowck/borrowck-move-error-with-note.stderr

@@ -11,10 +11,11 @@ LL |         Foo::Foo2(num) => (),
    |                   --- ...and here
    |
    = note: move occurs because these variables have types that don't implement the `Copy` trait
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -     match *f {
+LL +     match f {
    |
-LL |     match &*f {
-   |           +
 
 error[E0509]: cannot move out of type `S`, which implements the `Drop` trait
   --> $DIR/borrowck-move-error-with-note.rs:30:11

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

@@ -4,10 +4,11 @@ error[E0507]: cannot move out of `*x` which is behind a raw pointer
 LL |     let y = *x;
    |             ^^ move occurs because `*x` has type `Box<isize>`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -     let y = *x;
+LL +     let y = x;
    |
-LL |     let y = &*x;
-   |             +
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-move-out-of-overloaded-deref.stderr

@@ -4,10 +4,11 @@ error[E0507]: cannot move out of an `Rc`
 LL |     let _x = *Rc::new("hi".to_string());
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^ move occurs because value has type `String`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -     let _x = *Rc::new("hi".to_string());
+LL +     let _x = Rc::new("hi".to_string());
    |
-LL |     let _x = &*Rc::new("hi".to_string());
-   |              +
 
 error: aborting due to previous error
 

src/test/ui/borrowck/issue-20801.stderr

@@ -4,43 +4,47 @@ error[E0507]: cannot move out of a mutable reference
 LL |     let a = unsafe { *mut_ref() };
    |                      ^^^^^^^^^^ move occurs because value has type `T`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -     let a = unsafe { *mut_ref() };
+LL +     let a = unsafe { mut_ref() };
    |
-LL |     let a = unsafe { &*mut_ref() };
-   |                      +
 
 error[E0507]: cannot move out of a shared reference
   --> $DIR/issue-20801.rs:29:22
    |
 LL |     let b = unsafe { *imm_ref() };
    |                      ^^^^^^^^^^ move occurs because value has type `T`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -     let b = unsafe { *imm_ref() };
+LL +     let b = unsafe { imm_ref() };
    |
-LL |     let b = unsafe { &*imm_ref() };
-   |                      +
 
 error[E0507]: cannot move out of a raw pointer
   --> $DIR/issue-20801.rs:32:22
    |
 LL |     let c = unsafe { *mut_ptr() };
    |                      ^^^^^^^^^^ move occurs because value has type `T`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -     let c = unsafe { *mut_ptr() };
+LL +     let c = unsafe { mut_ptr() };
    |
-LL |     let c = unsafe { &*mut_ptr() };
-   |                      +
 
 error[E0507]: cannot move out of a raw pointer
   --> $DIR/issue-20801.rs:35:22
    |
 LL |     let d = unsafe { *const_ptr() };
    |                      ^^^^^^^^^^^^ move occurs because value has type `T`, which does not implement the `Copy` trait
    |
-help: consider borrowing here
+help: consider removing the dereference here
+   |
+LL -     let d = unsafe { *const_ptr() };
+LL +     let d = unsafe { const_ptr() };
    |
-LL |     let d = unsafe { &*const_ptr() };
-   |                      +
 
 error: aborting due to 4 previous errors