[test] stdlib/StringIndex: Spin off O(n^4) substring replacement test into a standalone long test

test/stdlib/StringIndex.swift

@@ -822,80 +822,3 @@ suite.test("String.replaceSubrange index validation")
     }
   }
 }
-
-suite.test("Substring.replaceSubrange index validation")
-.forEach(in: examples) { string in
-  guard #available(SwiftStdlib 5.7, *) else {
-    // Index navigation in 5.7 always rounds input indices down to the nearest
-    // Character, so that we always have a well-defined distance between
-    // indices, even if they aren't valid.
-    //
-    // 5.6 and below did not behave consistently in this case.
-    return
-  }
-
-  string.dumpIndices()
-
-  let scalarMap = string.scalarMap()
-  let allIndices = string.allIndices()
-
-  for i in allIndices {
-    print(i)
-    for j in allIndices {
-      guard i <= j else { continue }
-      let si = scalarMap[i]!.index
-      let sj = scalarMap[j]!.index
-
-      let substring = string[i ..< j]
-
-      let subindices = substring.allIndices()
-      for m in subindices {
-        for n in subindices {
-          guard m <= n else { continue }
-          let sm = scalarMap[m]!.index
-          let sn = scalarMap[n]!.index
-
-          let replacement = "x"
-
-          var _expected = "".unicodeScalars
-          _expected += string.unicodeScalars[si ..< sm]
-          _expected += replacement.unicodeScalars
-          _expected += string.unicodeScalars[sn ..< sj]
-          let expected = String(_expected)[...]
-
-          // Check Substring.replaceSubrange(_:with:)
-          do {
-            var actual = substring
-            actual.replaceSubrange(m ..< n, with: Array(replacement))
-
-            expectEqual(actual, expected,
-              """
-              string: \(string.debugDescription)
-              i:      \(i)
-              j:      \(j)
-              m:      \(m)
-              n:      \(n)
-              """)
-          }
-
-          // Check String.unicodeScalars.replaceSubrange(_:with:)
-          do {
-            var actual = substring
-            actual.unicodeScalars.replaceSubrange(
-              m ..< n, with: Array(replacement.unicodeScalars))
-
-            expectEqual(actual, expected,
-              """
-              string: \(string.debugDescription)
-              i:      \(i)
-              j:      \(j)
-              m:      \(m)
-              n:      \(n)
-              """)
-          }
-        }
-      }
-    }
-  }
-}
-

validation-test/stdlib/StringIndexLong.swift

@@ -0,0 +1,103 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+// REQUIRES: long_test
+
+import StdlibUnittest
+#if _runtime(_ObjC)
+import Foundation
+#endif
+
+var suite = TestSuite("StringIndexLong")
+defer { runAllTests() }
+
+let _examples: [StaticString] = [
+  "abc\r\ndefg",
+  "a\r\ncдe\u{301}日🧟‍♀️x🏳️‍🌈🇺🇸🇨🇦",
+]
+
+let examples: [String] = _examples.flatMap { s in
+  let str = "\(s)"
+  #if _runtime(_ObjC)
+  let unichars = Array(str.utf16)
+  let nsstr = NSString(characters: unichars, length: unichars.count)
+  return [str, nsstr as String]
+  #else
+  return [str]
+  #endif
+}
+
+suite.test("Substring.replaceSubrange index validation")
+.forEach(in: examples) { string in
+  guard #available(SwiftStdlib 5.7, *) else {
+    // Index navigation in 5.7 always rounds input indices down to the nearest
+    // Character, so that we always have a well-defined distance between
+    // indices, even if they aren't valid.
+    //
+    // 5.6 and below did not behave consistently in this case.
+    return
+  }
+
+  string.dumpIndices()
+
+  let scalarMap = string.scalarMap()
+  let allIndices = string.allIndices()
+
+  for i in allIndices {
+    print(i)
+    for j in allIndices {
+      guard i <= j else { continue }
+      let si = scalarMap[i]!.index
+      let sj = scalarMap[j]!.index
+
+      let substring = string[i ..< j]
+
+      let subindices = substring.allIndices()
+      for m in subindices {
+        for n in subindices {
+          guard m <= n else { continue }
+          let sm = scalarMap[m]!.index
+          let sn = scalarMap[n]!.index
+
+          let replacement = "x"
+
+          var _expected = "".unicodeScalars
+          _expected += string.unicodeScalars[si ..< sm]
+          _expected += replacement.unicodeScalars
+          _expected += string.unicodeScalars[sn ..< sj]
+          let expected = String(_expected)[...]
+
+          // Check Substring.replaceSubrange(_:with:)
+          do {
+            var actual = substring
+            actual.replaceSubrange(m ..< n, with: Array(replacement))
+
+            expectEqual(actual, expected,
+              """
+              string: \(string.debugDescription)
+              i:      \(i)
+              j:      \(j)
+              m:      \(m)
+              n:      \(n)
+              """)
+          }
+
+          // Check String.unicodeScalars.replaceSubrange(_:with:)
+          do {
+            var actual = substring
+            actual.unicodeScalars.replaceSubrange(
+              m ..< n, with: Array(replacement.unicodeScalars))
+
+            expectEqual(actual, expected,
+              """
+              string: \(string.debugDescription)
+              i:      \(i)
+              j:      \(j)
+              m:      \(m)
+              n:      \(n)
+              """)
+          }
+        }
+      }
+    }
+  }
+}