Implement Unicode scalars conversion

Sources/Parsing/Conversions/UnicodeScalarView.swift

@@ -0,0 +1,88 @@
+extension Conversion where Self == Conversions.SubstringToUnicodeScalarView {
+  /// A conversion from `Substring` to `Substring.UnicodeScalarView`.
+  @inlinable
+  public static var unicodeScalars: Self { .init() }
+}
+
+extension Conversion where Output == Substring {
+  /// Transforms this conversion to `Substring` into a conversion to `Substring.UnicodeScalarView`.
+  ///
+  /// A fluent version of ``Conversion/unicodeScalars-swift.type.property-7wivx``.
+  @inlinable
+  public var unicodeScalars: Conversions.Map<Self, Conversions.SubstringToUnicodeScalarView> {
+    self.map(.unicodeScalars)
+  }
+}
+
+extension Conversion where Self == Conversions.BytesToUnicodeScalarView<Substring.UTF8View> {
+  /// A conversion from `Substring.UTF8View` to `Substring.UnicodeScalarView`.
+  @inlinable
+  public static var unicodeScalars: Self { .init() }
+}
+
+extension Conversion where Output == Substring.UTF8View {
+  /// Transforms this conversion to `Substring.UTF8View` into a conversion to `Substring.UnicodeScalarView`.
+  ///
+  /// A fluent version of ``Conversion/unicodeScalars-swift.type.property-1nefn``.
+  @inlinable
+  public var unicodeScalars: Conversions.Map<Self, Conversions.BytesToUnicodeScalarView<Substring.UTF8View>> {
+    self.map(.unicodeScalars)
+  }
+}
+
+extension Conversion where Self == Conversions.BytesToUnicodeScalarView<ArraySlice<UInt8>> {
+  /// A conversion from `ArraySlice<UInt8>` to `Substring.UnicodeScalarView`.
+  @inlinable
+  public static var unicodeScalars: Self { .init() }
+}
+
+extension Conversion where Output == ArraySlice<UInt8> {
+  /// Transforms this conversion to `ArraySlice<UInt8>` into a conversion to `Substring.UnicodeScalarView`.
+  ///
+  /// A fluent version of ``Conversion/unicodeScalars-swift.type.property-24r1i``.
+  @inlinable
+  public var unicodeScalars: Conversions.Map<Self, Conversions.BytesToUnicodeScalarView<ArraySlice<UInt8>>> {
+    self.map(.unicodeScalars)
+  }
+}
+
+extension Conversions {
+  /// A conversion from a `Substring` to `Substring.UnicodeScalarView`.
+  ///
+  /// You will not typically need to interact with this type directly. Instead you will usually use
+  /// the ``Conversion/unicodeScalars-swift.type.property-7wivx`` operation, which constructs this type.
+  public struct SubstringToUnicodeScalarView: Conversion {
+    @inlinable
+    public init() {}
+
+    @inlinable
+    public func apply(_ input: Substring) throws -> Substring.UnicodeScalarView {
+      input.unicodeScalars
+    }
+
+    @inlinable
+    public func unapply(_ output: Substring.UnicodeScalarView) throws -> Substring {
+      Substring(output)
+    }
+  }
+
+  /// A conversion from a ``PrependableCollection`` of UTF-8 bytes to `Substring.UnicodeScalarView`.
+  ///
+  /// You will not typically need to interact with this type directly. Instead you will usually use
+  /// the ``Conversion/unicodeScalars-swift.type.property-1nefn`` and
+  /// ``Conversion/unicodeScalars-swift.type.property-24r1i`` operations, which construct this type.
+  public struct BytesToUnicodeScalarView<Input: PrependableCollection>: Conversion where Input.Element == UInt8 {
+    @inlinable
+    public init() {}
+
+    @inlinable
+    public func apply(_ input: Input) throws -> Substring.UnicodeScalarView {
+      Substring(decoding: input, as: UTF8.self).unicodeScalars
+    }
+
+    @inlinable
+    public func unapply(_ output: Substring.UnicodeScalarView) throws -> Input {
+      .init(Substring(output).utf8)
+    }
+  }
+}

Tests/ParsingTests/FromUnicodeScalarViewTests.swift

@@ -0,0 +1,94 @@
+import Parsing
+import XCTest
+
+final class FromUnicodeScalarViewTests: XCTestCase {
+  func testSubstring() {
+    let p = Parse(input: Substring.self) {
+      "caf"
+      From(.unicodeScalars) {
+        "\u{00E9}".unicodeScalars
+      }
+    }
+
+    var input = "caf\u{00E9}"[...]
+    XCTAssertNoThrow(try p.parse(&input))
+    XCTAssert(input.isEmpty)
+
+    XCTAssertThrowsError(try p.parse("cafe\u{0301}"))
+  }
+
+  func testUTF8View() {
+    let p = Parse(input: Substring.UTF8View.self) {
+      "caf".utf8
+      From(.unicodeScalars) {
+        "\u{00E9}".unicodeScalars
+      }
+    }
+
+    var input = "caf\u{00E9}"[...].utf8
+    XCTAssertNoThrow(try p.parse(&input))
+    XCTAssert(input.isEmpty)
+
+    XCTAssertThrowsError(try p.parse("cafe\u{0301}".utf8))
+  }
+
+  func testBytes() {
+    let p = Parse(input: ArraySlice<UInt8>.self) {
+      Array("caf".utf8)
+      From(.unicodeScalars) {
+        "\u{00E9}".unicodeScalars
+      }
+    }
+
+    var input = Array("caf\u{00E9}".utf8)[...]
+    XCTAssertNoThrow(try p.parse(&input))
+    XCTAssert(input.isEmpty)
+
+    XCTAssertThrowsError(try p.parse(Array("cafe\u{0301}".utf8)))
+  }
+
+  func testDeprecatedSubstring() {
+    let p = Parse(input: Substring.self) {
+      "caf"
+      FromUnicodeScalarView {
+        "\u{00E9}".unicodeScalars
+      }
+    }
+
+    var input = "caf\u{00E9}"[...]
+    XCTAssertNoThrow(try p.parse(&input))
+    XCTAssert(input.isEmpty)
+
+    XCTAssertThrowsError(try p.parse("cafe\u{0301}"))
+  }
+
+  func testDeprecatedUTF8View() {
+    let p = Parse(input: Substring.UTF8View.self) {
+      "caf".utf8
+      FromUnicodeScalarView {
+        "\u{00E9}".unicodeScalars
+      }
+    }
+
+    var input = "caf\u{00E9}"[...].utf8
+    XCTAssertNoThrow(try p.parse(&input))
+    XCTAssert(input.isEmpty)
+
+    XCTAssertThrowsError(try p.parse("cafe\u{0301}".utf8))
+  }
+
+  func testDeprecatedBytes() {
+    let p = Parse(input: ArraySlice<UInt8>.self) {
+      Array("caf".utf8)
+      FromUnicodeScalarView {
+        "\u{00E9}".unicodeScalars
+      }
+    }
+
+    var input = Array("caf\u{00E9}".utf8)[...]
+    XCTAssertNoThrow(try p.parse(&input))
+    XCTAssert(input.isEmpty)
+
+    XCTAssertThrowsError(try p.parse(Array("cafe\u{0301}".utf8)))
+  }
+}