Rollup merge of #122437 - Nadrieril:no-after-max, r=compiler-errors

pattern analysis: remove `MaybeInfiniteInt::JustAfterMax`

It was inherited from before half-open ranges, but it doesn't pull its weight anymore. We lose a tiny bit of diagnostic precision as can be seen in the test. I'm generally in favor of half-open ranges over explicit `x..=MAX` ranges anyway.

compiler/rustc_pattern_analysis/src/constructor.rs

@@ -195,8 +195,6 @@ pub enum MaybeInfiniteInt {
     /// Encoded value. DO NOT CONSTRUCT BY HAND; use `new_finite_{int,uint}`.
     #[non_exhaustive]
     Finite(u128),
-    /// The integer after `u128::MAX`. We need it to represent `x..=u128::MAX` as an exclusive range.
-    JustAfterMax,
     PosInfinity,
 }
 
@@ -232,18 +230,18 @@ impl MaybeInfiniteInt {
     pub fn minus_one(self) -> Option<Self> {
         match self {
             Finite(n) => n.checked_sub(1).map(Finite),
-            JustAfterMax => Some(Finite(u128::MAX)),
             x => Some(x),
         }
     }
-    /// Note: this will not turn a finite value into an infinite one or vice-versa.
+    /// Note: this will turn `u128::MAX` into `PosInfinity`. This means `plus_one` and `minus_one`
+    /// are not strictly inverses, but that poses no problem in our use of them.
+    /// this will not turn a finite value into an infinite one or vice-versa.
     pub fn plus_one(self) -> Option<Self> {
         match self {
             Finite(n) => match n.checked_add(1) {
                 Some(m) => Some(Finite(m)),
-                None => Some(JustAfterMax),
+                None => Some(PosInfinity),
             },
-            JustAfterMax => None,
             x => Some(x),
         }
     }
@@ -277,8 +275,7 @@ impl IntRange {
     }
 
     /// Construct a range with these boundaries.
-    /// `lo` must not be `PosInfinity` or `JustAfterMax`. `hi` must not be `NegInfinity`.
+    /// `lo` must not be `PosInfinity`. `hi` must not be `NegInfinity`.
-    /// If `end` is `Included`, `hi` must also not be `JustAfterMax`.
     #[inline]
     pub fn from_range(lo: MaybeInfiniteInt, mut hi: MaybeInfiniteInt, end: RangeEnd) -> IntRange {
         if end == RangeEnd::Included {

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -706,7 +706,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                     None => PatRangeBoundary::PosInfinity,
                 }
             }
-            JustAfterMax | PosInfinity => PatRangeBoundary::PosInfinity,
+            PosInfinity => PatRangeBoundary::PosInfinity,
         }
     }
 

tests/ui/half-open-range-patterns/half-open-range-pats-exhaustive-fail.stderr

@@ -394,17 +394,17 @@ help: ensure that all possible cases are being handled by adding a match arm wit
 LL |         match $s { $($t)+ => {}, u128::MAX => todo!() }
    |                                ++++++++++++++++++++++
 
-error[E0004]: non-exhaustive patterns: `340282366920938463463374607431768211454_u128..=u128::MAX` not covered
+error[E0004]: non-exhaustive patterns: `340282366920938463463374607431768211454_u128..` not covered
   --> $DIR/half-open-range-pats-exhaustive-fail.rs:93:12
    |
 LL |         m!(0, ..ALMOST_MAX);
-   |            ^ pattern `340282366920938463463374607431768211454_u128..=u128::MAX` not covered
+   |            ^ pattern `340282366920938463463374607431768211454_u128..` not covered
    |
    = note: the matched value is of type `u128`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
-LL |         match $s { $($t)+ => {}, 340282366920938463463374607431768211454_u128..=u128::MAX => todo!() }
+LL |         match $s { $($t)+ => {}, 340282366920938463463374607431768211454_u128.. => todo!() }
-   |                                +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+   |                                +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
 error[E0004]: non-exhaustive patterns: `0_u128` not covered
   --> $DIR/half-open-range-pats-exhaustive-fail.rs:94:12
@@ -754,17 +754,17 @@ help: ensure that all possible cases are being handled by adding a match arm wit
 LL |         match $s { $($t)+ => {}, i128::MAX => todo!() }
    |                                ++++++++++++++++++++++
 
-error[E0004]: non-exhaustive patterns: `170141183460469231731687303715884105726_i128..=i128::MAX` not covered
+error[E0004]: non-exhaustive patterns: `170141183460469231731687303715884105726_i128..` not covered
   --> $DIR/half-open-range-pats-exhaustive-fail.rs:161:12
    |
 LL |         m!(0, ..ALMOST_MAX);
-   |            ^ pattern `170141183460469231731687303715884105726_i128..=i128::MAX` not covered
+   |            ^ pattern `170141183460469231731687303715884105726_i128..` not covered
    |
    = note: the matched value is of type `i128`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
-LL |         match $s { $($t)+ => {}, 170141183460469231731687303715884105726_i128..=i128::MAX => todo!() }
+LL |         match $s { $($t)+ => {}, 170141183460469231731687303715884105726_i128.. => todo!() }
-   |                                +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+   |                                +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
 error[E0004]: non-exhaustive patterns: `i128::MIN` not covered
   --> $DIR/half-open-range-pats-exhaustive-fail.rs:162:12

tests/ui/pattern/usefulness/integer-ranges/exhaustiveness.stderr

@@ -107,17 +107,17 @@ help: ensure that all possible cases are being handled by adding a match arm wit
 LL |         match $s { $($t)+ => {}, u128::MAX => todo!() }
    |                                ++++++++++++++++++++++
 
-error[E0004]: non-exhaustive patterns: `5_u128..=u128::MAX` not covered
+error[E0004]: non-exhaustive patterns: `5_u128..` not covered
   --> $DIR/exhaustiveness.rs:61:8
    |
 LL |     m!(0u128, 0..=4);
-   |        ^^^^^ pattern `5_u128..=u128::MAX` not covered
+   |        ^^^^^ pattern `5_u128..` not covered
    |
    = note: the matched value is of type `u128`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
-LL |         match $s { $($t)+ => {}, 5_u128..=u128::MAX => todo!() }
+LL |         match $s { $($t)+ => {}, 5_u128.. => todo!() }
-   |                                +++++++++++++++++++++++++++++++
+   |                                +++++++++++++++++++++
 
 error[E0004]: non-exhaustive patterns: `0_u128` not covered
   --> $DIR/exhaustiveness.rs:62:8