Implement the Indic grapheme breaking rules

validation-test/stdlib/String.swift

@@ -2280,4 +2280,58 @@ StringTests.test("NormalizationCheck/Opaque")
 #endif
 }
 
+func expectBidirectionalCount(_ count: Int, _ string: String) {
+  var i = 0
+  var index = string.endIndex
+
+  while index != string.startIndex {
+    i += 1
+    string.formIndex(before: &index)
+  }
+
+  expectEqual(i, count)
+}
+
+StringTests.test("GraphemeBreaking.Indic Sequences") {
+  let test1 = "\u{0915}\u{0924}" // 2
+  expectEqual(2, test1.count)
+  expectBidirectionalCount(2, test1)
+
+  let test2 = "\u{0915}\u{094D}\u{0924}" // 1
+  expectEqual(1, test2.count)
+  expectBidirectionalCount(1, test2)
+
+  let test3 = "\u{0915}\u{094D}\u{094D}\u{0924}" // 1
+  expectEqual(1, test3.count)
+  expectBidirectionalCount(1, test3)
+
+  let test4 = "\u{0915}\u{094D}\u{200D}\u{0924}" // 1
+  expectEqual(1, test4.count)
+  expectBidirectionalCount(1, test4)
+
+  let test5 = "\u{0915}\u{093C}\u{200D}\u{094D}\u{0924}" // 1
+  expectEqual(1, test5.count)
+  expectBidirectionalCount(1, test5)
+
+  let test6 = "\u{0915}\u{093C}\u{094D}\u{200D}\u{0924}" // 1
+  expectEqual(1, test6.count)
+  expectBidirectionalCount(1, test6)
+
+  let test7 = "\u{0915}\u{094D}\u{0924}\u{094D}\u{092F}" // 1
+  expectEqual(1, test7.count)
+  expectBidirectionalCount(1, test7)
+
+  let test8 = "\u{0915}\u{094D}\u{0061}" // 2
+  expectEqual(2, test8.count)
+  expectBidirectionalCount(2, test8)
+
+  let test9 = "\u{0061}\u{094D}\u{0924}" // 2
+  expectEqual(2, test9.count)
+  expectBidirectionalCount(2, test9)
+
+  let test10 = "\u{003F}\u{094D}\u{0924}" // 2
+  expectEqual(2, test10.count)
+  expectBidirectionalCount(2, test10)
+}
+
 runAllTests()