Add a test case for u128::MAX - 1

src/librustc_mir/hair/pattern/_match.rs

@@ -1501,6 +1501,8 @@ enum Endpoint {
                     if let Endpoint::Both = a.1 {
                         split_ctors.push(IntRange::range_to_ctor(tcx, ty, a.0..=a.0));
                     }
+                    // Integer overflow cannot occur here, because only the first point may be
+                    // u128::MIN and only the last may be u128::MAX.
                     let c = match a.1 {
                         Endpoint::Start => a.0,
                         Endpoint::End | Endpoint::Both => a.0 + 1,

src/test/ui/exhaustive_integer_patterns.rs

@@ -140,21 +140,26 @@ fn main() {
     }
 
     match (0u8, true) { //~ ERROR non-exhaustive patterns
-        (0..=125, false) => {}
-        (128..=255, false) => {}
-        (0..=255, true) => {}
+        (0 ..= 125, false) => {}
+        (128 ..= 255, false) => {}
+        (0 ..= 255, true) => {}
     }
 
     match (0u8, true) { // ok
-        (0..=125, false) => {}
-        (128..=255, false) => {}
-        (0..=255, true) => {}
-        (125..128, false) => {}
+        (0 ..= 125, false) => {}
+        (128 ..= 255, false) => {}
+        (0 ..= 255, true) => {}
+        (125 .. 128, false) => {}
     }
 
     match 0u8 { // ok
-        0..2 => {}
-        1..=2 => {}
+        0 .. 2 => {}
+        1 ..= 2 => {}
         _ => {}
     }
+
+    const lim: u128 = u128::MAX - 1;
+    match 0u128 { //~ ERROR non-exhaustive patterns
+        0 ..= lim => {}
+    }
 }

src/test/ui/exhaustive_integer_patterns.stderr

@@ -64,6 +64,12 @@ error[E0004]: non-exhaustive patterns: `(126u8..=127u8, false)` not covered
 LL |     match (0u8, true) { //~ ERROR non-exhaustive patterns
    |           ^^^^^^^^^^^ pattern `(126u8..=127u8, false)` not covered
 
-error: aborting due to 10 previous errors
+error[E0004]: non-exhaustive patterns: `340282366920938463463374607431768211455u128` not covered
+  --> $DIR/exhaustive_integer_patterns.rs:162:11
+   |
+LL |     match 0u128 { //~ ERROR non-exhaustive patterns
+   |           ^^^^^ pattern `340282366920938463463374607431768211455u128` not covered
+
+error: aborting due to 11 previous errors
 
 For more information about this error, try `rustc --explain E0004`.