Add new error codes

src/librustc_borrowck/borrowck/mod.rs

@@ -708,7 +708,7 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
     fn bckerr_to_diag(&self, err: &BckError<'tcx>) -> DiagnosticBuilder<'a> {
         let span = err.span.clone();
 
-        let msg = match err.code {
+        match err.code {
             err_mutbl => {
                 let descr = match err.cmt.note {
                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
@@ -732,10 +732,11 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 
                 match err.cause {
                     MutabilityViolation => {
-                        format!("cannot assign to {}", descr)
+                        struct_span_err!(self.tcx.sess, span, E0594, "cannot assign to {}", descr)
                     }
                     BorrowViolation(euv::ClosureCapture(_)) => {
-                        format!("closure cannot assign to {}", descr)
+                        struct_span_err!(self.tcx.sess, span, E0595,
+                                         "closure cannot assign to {}", descr)
                     }
                     BorrowViolation(euv::OverloadedOperator) |
                     BorrowViolation(euv::AddrOf) |
@@ -744,7 +745,8 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
                     BorrowViolation(euv::AutoUnsafe) |
                     BorrowViolation(euv::ForLoop) |
                     BorrowViolation(euv::MatchDiscriminant) => {
-                        format!("cannot borrow {} as mutable", descr)
+                        struct_span_err!(self.tcx.sess, span, E0596,
+                                         "cannot borrow {} as mutable", descr)
                     }
                     BorrowViolation(euv::ClosureInvocation) => {
                         span_bug!(err.span,
@@ -759,17 +761,16 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
                         format!("`{}`", self.loan_path_to_string(&lp))
                     }
                 };
-                format!("{} does not live long enough", msg)
+                struct_span_err!(self.tcx.sess, span, E0597, "{} does not live long enough", msg)
             }
             err_borrowed_pointer_too_short(..) => {
                 let descr = self.cmt_to_path_or_string(&err.cmt);
-                format!("lifetime of {} is too short to guarantee \
-                         its contents can be safely reborrowed",
-                        descr)
+                struct_span_err!(self.tcx.sess, span, E0598,
+                                 "lifetime of {} is too short to guarantee \
+                                  its contents can be safely reborrowed",
+                                 descr)
             }
-        };
-
-        self.struct_span_err(span, &msg)
+        }
     }
 
     pub fn report_aliasability_violation(&self,
@@ -1176,7 +1177,7 @@ before rustc 1.16, this temporary lived longer - see issue #39283 \
                 if kind == ty::ClosureKind::Fn {
                     db.span_help(self.tcx.hir.span(upvar_id.closure_expr_id),
                                  "consider changing this closure to take \
-                                 self by mutable reference");
+                                  self by mutable reference");
                 }
             }
             _ => {

src/librustc_borrowck/diagnostics.rs

@@ -1114,9 +1114,63 @@ fn main() {
 ```
 "##,
 
+E0596: r##"
+This error occurs because you tried to mutably borrow a non-mutable variable.
+
+Example of erroneous code:
+
+```compile_fail,E0596
+let x = 1;
+let y = &mut x; // error: cannot borrow mutably
+```
+
+In here, `x` isn't mutable, so when we try to mutably borrow it in `y`, it
+fails. To fix this error, you need to make `x` mutable:
+
+```
+let mut x = 1;
+let y = &mut x; // ok!
+```
+"##,
+
+E0597: r##"
+This error occurs because a borrow was made inside a variable which has a
+greater lifetime than the borrowed one.
+
+Example of erroneous code:
+
+```compile_fail,E0597
+struct Foo<'a> {
+    x: Option<&'a u32>,
+}
+
+let mut x = Foo { x: None };
+let y = 0;
+x.x = Some(&y); // error: `y` does not live long enough
+```
+
+In here, `x` is created before `y` and therefore has a greater lifetime. Always
+keep in mind that values in a scope are dropped in the opposite order they are
+created. So to fix the previous example, just make the `y` lifetime greater than
+the `x`'s one:
+
+```
+struct Foo<'a> {
+    x: Option<&'a u32>,
+}
+
+let y = 0;
+let mut x = Foo { x: None };
+x.x = Some(&y);
+```
+"##,
+
 }
 
 register_diagnostics! {
 //    E0385, // {} in an aliasable location
     E0524, // two closures require unique access to `..` at the same time
+    E0594, // cannot assign to {}
+    E0595, // closure cannot assign to {}
+    E0598, // lifetime of {} is too short to guarantee its contents can be...
 }

src/test/compile-fail/E0596.rs

@@ -0,0 +1,14 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    let x = 1;
+    let y = &mut x; //~ ERROR E0596
+}

src/test/compile-fail/E0597.rs

@@ -0,0 +1,19 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Foo<'a> {
+    x: Option<&'a u32>,
+}
+
+fn main() {
+    let mut x = Foo { x: None };
+    let y = 0;
+    x.x = Some(&y);
+} //~ `y` does not live long enough [E0597]