Add support for suggesting as_ref to Result accesses

Author: estebank

src/librustc_mir/borrow_check/move_errors.rs

@@ -319,10 +319,16 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                         original_path.ty(self.mir, self.infcx.tcx).ty,
                     );
                     let snippet = self.infcx.tcx.sess.source_map().span_to_snippet(span).unwrap();
-                    if orig_path_ty.starts_with("std::option::Option") {
+                    let is_option = orig_path_ty.starts_with("std::option::Option");
+                    let is_result = orig_path_ty.starts_with("std::result::Result");
+                    if  is_option || is_result {
                         err.span_suggestion(
                             span,
-                            "consider borrowing the `Option`'s content",
+                            &format!("consider borrowing the `{}`'s content", if is_option {
+                                "Option"
+                            } else {
+                                "Result"
+                            }),
                             format!("{}.as_ref()", snippet),
                             Applicability::MaybeIncorrect,
                         );

src/test/ui/suggestions/option-content-move.fixed

@@ -18,4 +18,22 @@ impl LipogramCorpora {
     }
 }
 
+pub struct LipogramCorpora2 {
+    selections: Vec<(char, Result<String, String>)>,
+}
+
+impl LipogramCorpora2 {
+    pub fn validate_all(&mut self) -> Result<(), char> {
+        for selection in &self.selections {
+            if selection.1.is_ok() {
+                if selection.1.as_ref().unwrap().contains(selection.0) {
+                //~^ ERROR cannot move out of borrowed content
+                    return Err(selection.0);
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
 fn main() {}

src/test/ui/suggestions/option-content-move.rs

@@ -18,4 +18,22 @@ impl LipogramCorpora {
     }
 }
 
+pub struct LipogramCorpora2 {
+    selections: Vec<(char, Result<String, String>)>,
+}
+
+impl LipogramCorpora2 {
+    pub fn validate_all(&mut self) -> Result<(), char> {
+        for selection in &self.selections {
+            if selection.1.is_ok() {
+                if selection.1.unwrap().contains(selection.0) {
+                //~^ ERROR cannot move out of borrowed content
+                    return Err(selection.0);
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
 fn main() {}

src/test/ui/suggestions/option-content-move.stderr

@@ -7,6 +7,15 @@ LL |                 if selection.1.unwrap().contains(selection.0) {
    |                    cannot move out of borrowed content
    |                    help: consider borrowing the `Option`'s content: `selection.1.as_ref()`
 
-error: aborting due to previous error
+error[E0507]: cannot move out of borrowed content
+  --> $DIR/option-content-move.rs:29:20
+   |
+LL |                 if selection.1.unwrap().contains(selection.0) {
+   |                    ^^^^^^^^^^^
+   |                    |
+   |                    cannot move out of borrowed content
+   |                    help: consider borrowing the `Result`'s content: `selection.1.as_ref()`
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0507`.