Fix show error message when literal overflows in match patterns

compiler/rustc_mir_build/src/thir/constant.rs

@@ -17,7 +17,13 @@ crate fn lit_to_const<'tcx>(
         let param_ty = ParamEnv::reveal_all().and(ty);
         let width = tcx.layout_of(param_ty).map_err(|_| LitToConstError::Reported)?.size;
         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
-        let result = width.truncate(n);
+        let result = match &ty.kind() {
+            ty::Uint(_) => {
+                let max_value = width.unsigned_int_max();
+                if n >= max_value { max_value } else { width.truncate(n) }
+            }
+            _ => width.truncate(n),
+        };
         trace!("trunc result: {}", result);
         Ok(ConstValue::Scalar(Scalar::from_uint(result, width)))
     };

src/test/ui/error-codes/E0081.rs

@@ -10,10 +10,10 @@ enum Enum {
 #[repr(u8)]
 enum EnumOverflowRepr {
     P = 257,
-    //~^ NOTE first use of `1` (overflowed from `257`)
+    //~^ NOTE first use of `255` (overflowed from `257`)
     X = 513,
-    //~^ ERROR discriminant value `1` already exists
-    //~| NOTE enum already has `1` (overflowed from `513`)
+    //~^ ERROR discriminant value `255` already exists
+    //~| NOTE enum already has `255` (overflowed from `513`)
 }
 
 fn main() {

src/test/ui/error-codes/E0081.stderr

@@ -7,14 +7,14 @@ LL |
 LL |     X = 3,
    |         ^ enum already has `3`
 
-error[E0081]: discriminant value `1` already exists
+error[E0081]: discriminant value `255` already exists
   --> $DIR/E0081.rs:14:9
    |
 LL |     P = 257,
-   |         --- first use of `1` (overflowed from `257`)
+   |         --- first use of `255` (overflowed from `257`)
 LL |
 LL |     X = 513,
-   |         ^^^ enum already has `1` (overflowed from `513`)
+   |         ^^^ enum already has `255` (overflowed from `513`)
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-94239.rs

@@ -0,0 +1,8 @@
+pub const fn test_match_range(len: u64) -> u64 {
+    match len {
+        10000000000000000000..=99999999999999999999 => 0, //~ ERROR literal out of range for `u64`
+        _ => unreachable!(),
+    }
+}
+
+fn main() {}

src/test/ui/issues/issue-94239.stderr

@@ -0,0 +1,11 @@
+error: literal out of range for `u64`
+  --> $DIR/issue-94239.rs:3:32
+   |
+LL |         10000000000000000000..=99999999999999999999 => 0,
+   |                                ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[deny(overflowing_literals)]` on by default
+   = note: the literal `99999999999999999999` does not fit into the type `u64` whose range is `0..=18446744073709551615`
+
+error: aborting due to previous error
+