Simple operators for character value comparisons.

stdlib/public/core/UnicodeScalar.swift

@@ -364,6 +364,15 @@ extension UInt8 {
         "Code point value does not fit into ASCII")
     self = UInt8(v.value)
   }
+  /// Initializes a UInt8 with the ASCII value of the provided Unicode scalar if possible.
+  ///
+  /// - Parameter unicode: The Unicode scalar to initialize from.
+  /// - Note: Construct with value `v.value`.
+  @inlinable @_alwaysEmitIntoClient
+  public init?(ifASCII v: Unicode.Scalar) {
+    guard v.value < 128 else { return nil }
+    self = Self(v.value)
+  }
 }
 extension UInt32 {
   /// Construct with value `v.value`.
@@ -380,6 +389,67 @@ extension UInt64 {
   }
 }
 
+/// Extends `Optional<UInt8>` to allow direct comparisons with double quoted literals.
+extension UInt8? {
+  /// Returns a Boolean value indicating whether the optional `UInt8` is equal to the provided Unicode scalar.
+  ///
+  /// - Parameters:
+  ///   - i: The optional `UInt8` value to compare.
+  ///   - s: The Unicode scalar to compare against.
+  /// - Returns: `true` if the optional `UInt8` is equal to the provided Unicode scalar; otherwise, `false`.
+  @_transparent @_alwaysEmitIntoClient
+  public static func == (i: Self, s: Unicode.Scalar) -> Bool {
+    return i == UInt8(ifASCII: s)
+  }
+
+  /// Returns a Boolean value indicating whether the optional `UInt8` is not equal to the provided Unicode scalar.
+  @_transparent @_alwaysEmitIntoClient
+  public static func != (i: Self, s: Unicode.Scalar) -> Bool {
+    return i != UInt8(ifASCII: s)
+  }
+  /// Returns a Boolean value indicating whether the optional `UInt8` is equal to the provided Unicode scalar.
+  ///
+  /// - Parameters:
+  ///   - s: The Unicode scalar to compare against.
+  ///   - i: The optional `UInt8` value to compare.
+  /// - Returns: `true` if the optional `UInt8` is equal to the provided Unicode scalar; otherwise, `false`.
+  @_transparent @_alwaysEmitIntoClient
+  public static func == (s: Unicode.Scalar, i: Self) -> Bool {
+    return i == UInt8(ifASCII: s)
+  }
+
+  /// Returns a Boolean value indicating whether the optional `UInt8` is not equal to the provided Unicode scalar.
+  @_transparent @_alwaysEmitIntoClient
+  public static func != (s: Unicode.Scalar, i: Self) -> Bool {
+    return i != UInt8(ifASCII: s)
+  }
+
+  /// Allows pattern matching of Unicode scalars in switch statements.
+  @_transparent @_alwaysEmitIntoClient
+  public static func ~= (s: Unicode.Scalar, i: Self) -> Bool {
+    return i == UInt8(ifASCII: s)
+  }
+}
+
+/// Extends `FixedWidthInteger` providing initialization from a Unicode scalar.
+extension FixedWidthInteger {
+  /// Initializes a FixedWidthInteger with the value of the provided Unicode scalar.
+  ///
+  /// - Parameter unicode: The Unicode scalar to initialize from.
+  /// - Note: Construct with value `v.value`.
+  @inlinable @_alwaysEmitIntoClient
+  public init?(unicode v: Unicode.Scalar) {
+    guard v.value <= Self.max else { return nil }
+    self = Self(v.value)
+  }
+  /// Converts an ASCII value into a UnicodeScalar
+  @inlinable @_alwaysEmitIntoClient
+  public var asciiScalar: Unicode.Scalar? {
+    guard self < 128 && self >= 0 else { return nil }
+    return Unicode.Scalar(UInt8(self))
+  }
+}
+
 extension Unicode.Scalar: Equatable {
   @inlinable
   public static func == (lhs: Unicode.Scalar, rhs: Unicode.Scalar) -> Bool {

test/Constraints/patterns.swift

@@ -631,9 +631,7 @@ func testExprPatternIsolation() {
   }
   for case 0 in nil {} // expected-error {{'nil' requires a contextual type}}
   for case 0 in [nil] {}
-  // expected-error@-1 {{type 'Any' cannot conform to 'Equatable'}}
-  // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
-  // expected-note@-3 {{requirement from conditional conformance of 'Any?' to 'Equatable'}}
+  // expected-error@-1 {{expression pattern of type 'Int' cannot match values of type 'Any?'}}
 
   // Though we will try Double for an integer literal...
   let d: Double = 0
@@ -679,7 +677,7 @@ func testExprPatternIsolation() {
 
   // FIXME: Bad error (https://github.com/apple/swift/issues/64279)
   if case .e(nil, 0) = produceMultiPayload() {}
-  // expected-error@-1 {{expression pattern of type 'String' cannot match values of type 'Substring'}}
+  // expected-error@-1 {{expression pattern of type 'Unicode.Scalar' cannot match values of type 'UInt8'}}
   // expected-note@-2 {{overloads for '~=' exist with these partially matching parameter lists}}
 
   if case .e(5, nil) = produceMultiPayload() as MultiPayload<Int?> {}

test/Constraints/rdar105782480.swift

@@ -11,8 +11,8 @@ func foo(value: MyEnum) {
   takeClosure {
     switch value {
     case .second(let drag).invalid:
-      // expected-error@-1 {{value of type 'MyEnum' has no member 'invalid'}}
-      // expected-error@-2 {{'let' binding pattern cannot appear in an expression}}
+      // expected-error@-1 {{expression pattern of type 'Unicode.Scalar' cannot match values of type 'MyEnum'}}
+      // expected-error@-2 {{type 'Unicode.Scalar' has no member 'second'}}
       break
     }
   }

test/Misc/character_ops.swift

@@ -0,0 +1,64 @@
+// RUN: %target-run-simple-swift | %FileCheck %s
+// REQUIRES: executable_test
+
+let c = UInt8(ascii: "a")
+
+// CHECK: OK
+if c == "a" {
+  print("OK")
+}
+
+// CHECK: OK
+if c != "b" {
+  print("OK")
+}
+
+// CHECK: OK
+switch c {
+case "a":
+  print("OK")
+case "b":
+  fallthrough
+default:
+  print("FAIL")
+}
+
+let d: UInt8? = UInt8(ascii: "a")
+
+// CHECK: OK
+if d == "a" {
+  print("OK")
+}
+
+// CHECK: OK
+if d != "b" {
+  print("OK")
+}
+
+// CHECK: OK
+switch d {
+case "a":
+  print("OK")
+case "b":
+  fallthrough
+default:
+  print("FAIL")
+}
+
+// CHECK: OK
+switch d?.asciiScalar {
+case "a":
+  print("OK")
+case "b":
+  fallthrough
+default:
+  print("FAIL")
+}
+
+// CHECK: OK
+if UInt8(unicode: "a") == "a" {
+  print("OK")
+}
+
+// CHECK: 128512
+print(UInt64(unicode: "😀"))

test/abi/Inputs/macOS/arm64/stdlib/baseline-asserts

@@ -7042,6 +7042,7 @@ _$ss17FixedWidthIntegerPSzTb
 _$ss17FixedWidthIntegerPs25LosslessStringConvertibleTb
 _$ss17FixedWidthIntegerPsE03bitB0Sivg
 _$ss17FixedWidthIntegerPsE03bitB0SivpMV
+_$ss17FixedWidthIntegerPsE11asciiScalars7UnicodeO0E0VSgvpMV
 _$ss17FixedWidthIntegerPsE12littleEndianxvg
 _$ss17FixedWidthIntegerPsE12littleEndianxvpMV
 _$ss17FixedWidthIntegerPsE12littleEndianxx_tcfC

test/stmt/typed_throws.swift

@@ -80,8 +80,8 @@ func testDoCatchMultiErrorType() {
   do {
     try doSomething()
     try doHomework()
-  } catch .failed { // expected-error{{type 'any Error' has no member 'failed'}}
-
+  } catch .failed { // expected-error{{expression pattern of type 'Unicode.Scalar' cannot match values of type 'any Error}}
+    // expected-error@-1{{type 'Unicode.Scalar' has no member 'failed'}}
   } catch {
     let _: Int = error // expected-error{{cannot convert value of type 'any Error' to specified type 'Int'}}
   }