[SE-0494][stdlib] Add isTriviallyIdentical for unicode views

stdlib/public/core/StringUTF16View.swift

@@ -1056,3 +1056,14 @@ extension String.UTF16View {
     }
   }
 }
+
+extension String.UTF16View {
+  /// Returns a boolean value indicating whether this UTF16 view
+  /// is trivially identical to `other`.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    self._guts.rawBits == other._guts.rawBits
+  }
+}

stdlib/public/core/StringUTF8View.swift

@@ -684,3 +684,14 @@ extension String.UTF8View {
     return unsafe try _guts.withFastUTF8(body)
   }
 }
+
+extension String.UTF8View {
+  /// Returns a boolean value indicating whether this UTF8 view
+  /// is trivially identical to `other`.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    self._guts.rawBits == other._guts.rawBits
+  }
+}

stdlib/public/core/StringUnicodeScalarView.swift

@@ -527,3 +527,14 @@ extension String.UnicodeScalarView {
     return r._knownUTF16
   }
 }
+
+extension String.UnicodeScalarView {
+  /// Returns a boolean value indicating whether this unicode scalar view
+  /// is trivially identical to `other`.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    self._guts.rawBits == other._guts.rawBits
+  }
+}

stdlib/public/core/Substring.swift

@@ -882,6 +882,18 @@ extension Substring.UTF8View {
 #endif // !(os(watchOS) && _pointerBitWidth(_32))
 }
 
+extension Substring.UTF8View {
+  /// Returns a boolean value indicating whether this UTF8 view
+  /// is trivially identical to `other`.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    self._base.isTriviallyIdentical(to: other._base)
+    && self._bounds == other._bounds
+  }
+}
+
 extension Substring {
   @inlinable
   public var utf8: UTF8View {
@@ -1037,6 +1049,18 @@ extension Substring.UTF16View: BidirectionalCollection {
   }
 }
 
+extension Substring.UTF16View {
+  /// Returns a boolean value indicating whether this UTF16 view
+  /// is trivially identical to `other`.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    self._base.isTriviallyIdentical(to: other._base)
+    && self._bounds == other._bounds
+  }
+}
+
 extension Substring {
   @inlinable
   public var utf16: UTF16View {
@@ -1281,6 +1305,18 @@ extension Substring.UnicodeScalarView: RangeReplaceableCollection {
   }
 }
 
+extension Substring.UnicodeScalarView {
+  /// Returns a boolean value indicating whether this unicode scalar view
+  /// is trivially identical to `other`.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    self._slice._base.isTriviallyIdentical(to: other._slice._base)
+    && self._bounds == other._bounds
+  }
+}
+
 extension Substring: RangeReplaceableCollection {
   @_specialize(where S == String)
   @_specialize(where S == Substring)

test/stdlib/StringAPI.swift

@@ -522,6 +522,94 @@ StringTests.test("_isIdentical(to:)") {
   expectTrue(g._isIdentical(to: g))
 }
 
+StringTests.test("String.UnicodeScalarView.isTriviallyIdentical(to:)") {
+  let a = "Hello".unicodeScalars
+  let b = "Hello".unicodeScalars
+  expectTrue(a.isTriviallyIdentical(to: a))
+  expectTrue(b.isTriviallyIdentical(to: b))
+  expectTrue(a.isTriviallyIdentical(to: b))
+  expectTrue(b.isTriviallyIdentical(to: a))
+
+  let c = "Abcde".unicodeScalars
+  expectFalse(a.isTriviallyIdentical(to: c))
+  expectFalse(c.isTriviallyIdentical(to: a))
+}
+StringTests.test("String.UTF8View.isTriviallyIdentical(to:)") {
+  let a = "Hello".utf8
+  let b = "Hello".utf8
+  expectTrue(a.isTriviallyIdentical(to: a))
+  expectTrue(b.isTriviallyIdentical(to: b))
+  expectTrue(a.isTriviallyIdentical(to: b))
+  expectTrue(b.isTriviallyIdentical(to: a))
+
+
+  let c = "Abcde".utf8
+  expectFalse(a.isTriviallyIdentical(to: c))
+  expectFalse(c.isTriviallyIdentical(to: a))
+}
+StringTests.test("String.UTF16View.isTriviallyIdentical(to:)") {
+  let a = "Hello".utf16
+  let b = "Hello".utf16
+  expectTrue(a.isTriviallyIdentical(to: a))
+  expectTrue(b.isTriviallyIdentical(to: b))
+  expectTrue(a.isTriviallyIdentical(to: b))
+  expectTrue(b.isTriviallyIdentical(to: a))
+
+
+  let c = "Abcde".utf16
+  expectFalse(a.isTriviallyIdentical(to: c))
+  expectFalse(c.isTriviallyIdentical(to: a))
+}
+
+StringTests.test("Substring.UnicodeScalarView.isTriviallyIdentical(to:)") {
+  let base1 = "Test String"
+  let a = base1[base1.index(base1.startIndex, offsetBy: 5)..<base1.endIndex]
+    .unicodeScalars
+  let b = base1[base1.index(base1.startIndex, offsetBy: 5)..<base1.endIndex]
+    .unicodeScalars
+  expectTrue(a.isTriviallyIdentical(to: a))
+  expectTrue(b.isTriviallyIdentical(to: b))
+  expectTrue(a.isTriviallyIdentical(to: b))
+  expectTrue(b.isTriviallyIdentical(to: a))
+
+  let c = base1[base1.startIndex..<base1.index(base1.startIndex, offsetBy: 5)]
+    .unicodeScalars
+  expectFalse(a.isTriviallyIdentical(to: c))
+  expectFalse(c.isTriviallyIdentical(to: a))
+}
+StringTests.test("Substring.UTF8View.isTriviallyIdentical(to:)") {
+  let base1 = "Test String"
+  let a = base1[base1.index(base1.startIndex, offsetBy: 5)..<base1.endIndex]
+    .utf8
+  let b = base1[base1.index(base1.startIndex, offsetBy: 5)..<base1.endIndex]
+    .utf8
+  expectTrue(a.isTriviallyIdentical(to: a))
+  expectTrue(b.isTriviallyIdentical(to: b))
+  expectTrue(a.isTriviallyIdentical(to: b))
+  expectTrue(b.isTriviallyIdentical(to: a))
+
+  let c = base1[base1.startIndex..<base1.index(base1.startIndex, offsetBy: 5)]
+    .utf8
+  expectFalse(a.isTriviallyIdentical(to: c))
+  expectFalse(c.isTriviallyIdentical(to: a))
+}
+StringTests.test("Substring.UTF16View.isTriviallyIdentical(to:)") {
+  let base1 = "Test String"
+  let a = base1[base1.index(base1.startIndex, offsetBy: 5)..<base1.endIndex]
+    .utf16
+  let b = base1[base1.index(base1.startIndex, offsetBy: 5)..<base1.endIndex]
+    .utf16
+  expectTrue(a.isTriviallyIdentical(to: a))
+  expectTrue(b.isTriviallyIdentical(to: b))
+  expectTrue(a.isTriviallyIdentical(to: b))
+  expectTrue(b.isTriviallyIdentical(to: a))
+
+  let c = base1[base1.startIndex..<base1.index(base1.startIndex, offsetBy: 5)]
+    .utf16
+  expectFalse(a.isTriviallyIdentical(to: c))
+  expectFalse(c.isTriviallyIdentical(to: a))
+}
+
 StringTests.test("hasPrefix/hasSuffix vs Character boundaries") {
   // https://github.com/apple/swift/issues/67427
   let s1 = "\r\n"