Improve div by zero const eval errors

Author: Oliver Schneider

src/librustc/mir/mod.rs

@@ -1134,7 +1134,7 @@ impl<'tcx> TerminatorKind<'tcx> {
                     write!(fmt, "!")?;
                 }
                 write!(fmt, "{:?}, ", cond)?;
-                write!(fmt, "{:?}", msg)?;
+                write!(fmt, "\"{:?}\"", msg)?;
 
                 write!(fmt, ")")
             },

src/librustc_mir/interpret/operator.rs

@@ -140,7 +140,8 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
                 return Ok((PrimVal::from_bool(op(&l, &r)), false));
             }
             let op: Option<fn(i128, i128) -> (i128, bool)> = match bin_op {
-                Rem | Div if r == 0 => return Ok((PrimVal::Bytes(l), true)),
+                Div if r == 0 => return err!(DivisionByZero),
+                Rem if r == 0 => return err!(RemainderByZero),
                 Div => Some(i128::overflowing_div),
                 Rem => Some(i128::overflowing_rem),
                 Add => Some(i128::overflowing_add),
@@ -221,7 +222,8 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
                     Add => u128::overflowing_add,
                     Sub => u128::overflowing_sub,
                     Mul => u128::overflowing_mul,
-                    Rem | Div if r == 0 => return Ok((PrimVal::Bytes(l), true)),
+                    Div if r == 0 => return err!(DivisionByZero),
+                    Rem if r == 0 => return err!(RemainderByZero),
                     Div => u128::overflowing_div,
                     Rem => u128::overflowing_rem,
                     _ => bug!(),

src/librustc_mir/interpret/terminator/mod.rs

@@ -161,6 +161,8 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
                         }
                         Overflow(op) => Err(Overflow(op).into()),
                         OverflowNeg => Err(OverflowNeg.into()),
+                        DivisionByZero => Err(DivisionByZero.into()),
+                        RemainderByZero => Err(RemainderByZero.into()),
                         GeneratorResumedAfterReturn |
                         GeneratorResumedAfterPanic => unimplemented!(),
                         _ => bug!(),

src/test/ui/const-eval/index_out_of_bound.stderr

@@ -2,7 +2,7 @@ error[E0080]: constant evaluation error
   --> $DIR/index_out_of_bound.rs:11:19
    |
 LL | static FOO: i32 = [][0];
-   |                   ^^^^^ index out of bounds: the len is 0 but the index is 0 at $DIR/index_out_of_bound.rs:11:19: 11:24
+   |                   ^^^^^ index out of bounds: the len is 0 but the index is 0
 
 error: aborting due to previous error
 

src/test/ui/const-eval/promoted_errors.stderr

@@ -28,7 +28,7 @@ warning: constant evaluation error
   --> $DIR/promoted_errors.rs:19:20
    |
 LL |     println!("{}", 1/(1-1));
-   |                    ^^^^^^^ attempt to divide with overflow
+   |                    ^^^^^^^ attempt to divide by zero
 
 warning: attempt to divide by zero
   --> $DIR/promoted_errors.rs:22:14
@@ -40,11 +40,11 @@ warning: constant evaluation error
   --> $DIR/promoted_errors.rs:22:14
    |
 LL |     let _x = 1/(1-1);
-   |              ^^^^^^^ attempt to divide with overflow
+   |              ^^^^^^^ attempt to divide by zero
 
 warning: constant evaluation error
   --> $DIR/promoted_errors.rs:25:20
    |
 LL |     println!("{}", 1/(false as u32));
-   |                    ^^^^^^^^^^^^^^^^ attempt to divide with overflow
+   |                    ^^^^^^^^^^^^^^^^ attempt to divide by zero
 

src/test/ui/error-codes/E0080.rs

@@ -15,7 +15,6 @@ enum Enum {
     //~| const_err
     //~| const_err
     //~| const_err
-    //~| divide by zero
 }
 
 fn main() {

src/test/ui/error-codes/E0080.stderr

@@ -24,7 +24,7 @@ warning: constant evaluation error
   --> $DIR/E0080.rs:14:9
    |
 LL |     Y = (1 / 0) //~ ERROR E0080
-   |         ^^^^^^^ attempt to divide with overflow
+   |         ^^^^^^^ attempt to divide by zero
 
 error[E0080]: constant evaluation error
   --> $DIR/E0080.rs:14:9