Auto merge of #50653 - oli-obk:bad_const, r=cramertj

Make the `const_err` lint `deny`-by-default

At best these things are runtime panics (debug mode) or overflows (release mode). More likely they are public constants that are unused in the crate declaring them.

This is not a breaking change, as dependencies won't break and root crates can `#![warn(const_err)]`, though I don't know why anyone would do that.

Author: bors

src/librustc/lint/builtin.rs

@@ -27,7 +27,7 @@ declare_lint! {
 
 declare_lint! {
     pub CONST_ERR,
-    Warn,
+    Deny,
     "constant evaluation detected erroneous expression"
 }
 

src/test/compile-fail/array_const_index-0.rs

@@ -10,9 +10,8 @@
 
 const A: &'static [i32] = &[];
 const B: i32 = (&A)[1];
-//~^ ERROR constant evaluation error
-//~| index out of bounds: the len is 0 but the index is 1
-//~| WARN this constant cannot be used
+//~^ index out of bounds: the len is 0 but the index is 1
+//~| ERROR this constant cannot be used
 
 fn main() {
     let _ = B;

src/test/compile-fail/array_const_index-1.rs

@@ -10,9 +10,8 @@
 
 const A: [i32; 0] = [];
 const B: i32 = A[1];
-//~^ ERROR constant evaluation error
-//~| index out of bounds: the len is 0 but the index is 1
-//~| WARN this constant cannot be used
+//~^ index out of bounds: the len is 0 but the index is 1
+//~| ERROR this constant cannot be used
 
 fn main() {
     let _ = B;

src/test/compile-fail/const-slice-oob.rs

@@ -12,9 +12,8 @@
 
 const FOO: &'static[u32] = &[1, 2, 3];
 const BAR: u32 = FOO[5];
-//~^ ERROR constant evaluation error [E0080]
-//~| index out of bounds: the len is 3 but the index is 5
-//~| WARN this constant cannot be used
+//~^ index out of bounds: the len is 3 but the index is 5
+//~| ERROR this constant cannot be used
 
 fn main() {
     let _ = BAR;

src/test/compile-fail/eval-enum.rs

@@ -12,11 +12,11 @@ enum Test {
     DivZero = 1/0,
     //~^ attempt to divide by zero
     //~| ERROR constant evaluation error
-    //~| WARN constant evaluation error
+    //~| ERROR constant evaluation error
     RemZero = 1%0,
     //~^ attempt to calculate the remainder with a divisor of zero
     //~| ERROR constant evaluation error
-    //~| WARN constant evaluation error
+    //~| ERROR constant evaluation error
 }
 
 fn main() {}

src/test/incremental/warnings-reemitted.rs

@@ -13,6 +13,7 @@
 // compile-pass
 
 #![allow(warnings)]
+#![warn(const_err)]
 
 fn main() {
     255u8 + 1; //~ WARNING this expression will panic at run-time

src/test/run-fail/overflowing-add.rs

@@ -11,6 +11,8 @@
 // error-pattern:thread 'main' panicked at 'attempt to add with overflow'
 // compile-flags: -C debug-assertions
 
+#![allow(const_err)]
+
 fn main() {
     let _x = 200u8 + 200u8 + 200u8;
 }

src/test/run-fail/overflowing-mul.rs

@@ -11,6 +11,8 @@
 // error-pattern:thread 'main' panicked at 'attempt to multiply with overflow'
 // compile-flags: -C debug-assertions
 
+#![allow(const_err)]
+
 fn main() {
     let x = 200u8 * 4;
 }

src/test/run-fail/overflowing-neg.rs

@@ -11,6 +11,8 @@
 // error-pattern:thread 'main' panicked at 'attempt to negate with overflow'
 // compile-flags: -C debug-assertions
 
+#![allow(const_err)]
+
 fn main() {
     let _x = -std::i8::MIN;
 }

src/test/run-fail/overflowing-sub.rs

@@ -11,6 +11,8 @@
 // error-pattern:thread 'main' panicked at 'attempt to subtract with overflow'
 // compile-flags: -C debug-assertions
 
+#![allow(const_err)]
+
 fn main() {
     let _x = 42u8 - (42u8 + 1);
 }