Make emoji properties Darwin only.

Ubuntu 16.04 doesn't have a recent enough ICU to support these; we need a better long-term solution, such as bundling ICU with the toolchain.

Author: allevato

stdlib/public/core/UnicodeScalarProperties.swift

@@ -581,6 +581,12 @@ extension Unicode.Scalar.Properties {
     return _hasBinaryProperty(__swift_stdlib_UCHAR_CHANGES_WHEN_NFKC_CASEFOLDED)
   }
 
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+  // FIXME: These properties were introduced in ICU 57, but Ubuntu 16.04 comes
+  // with ICU 55 so the values won't be correct there. Exclude them on
+  // non-Darwin platforms for now; bundling ICU with the toolchain would resolve
+  // this and other inconsistencies (https://bugs.swift.org/browse/SR-6076).
+
   /// A Boolean property indicating whether the scalar has an emoji
   /// presentation, whether or not it is the default.
   ///
@@ -656,6 +662,7 @@ extension Unicode.Scalar.Properties {
   public var isEmojiModifierBase: Bool {
     return _hasBinaryProperty(__swift_stdlib_UCHAR_EMOJI_MODIFIER_BASE)
   }
+#endif
 }
 
 /// Case mapping properties.

test/stdlib/UnicodeScalarPropertiesTests.swift

@@ -81,6 +81,8 @@ UnicodeScalarPropertiesTests.test("properties.booleanProperties") {
   expectBooleanProperty(\.changesWhenCaseFolded, trueFor: "A", falseFor: "!")
   expectBooleanProperty(\.changesWhenCaseMapped, trueFor: "A", falseFor: "!")
   expectBooleanProperty(\.changesWhenNFKCCaseFolded, trueFor: "A", falseFor: "!")
+
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
   // U+2708 AIRPLANE
   expectBooleanProperty(\.isEmoji, trueFor: "\u{2708}", falseFor: "A")
   // U+231A WATCH
@@ -89,6 +91,7 @@ UnicodeScalarPropertiesTests.test("properties.booleanProperties") {
   expectBooleanProperty(\.isEmojiModifier, trueFor: "\u{1F3FD}", falseFor: "A")
   // U+270B RAISED HAND
   expectBooleanProperty(\.isEmojiModifierBase, trueFor: "\u{270B}", falseFor: "A")
+#endif
 }
 
 UnicodeScalarPropertiesTests.test("properties.lowercaseMapping") {