From 6787b733348c07b4fc5d9c3454c6ffff61a0f2a2 Mon Sep 17 00:00:00 2001
From: David Smith <david_smith@apple.com>
Date: Tue, 31 Aug 2021 08:51:33 -0700
Subject: [PATCH 1/2] Keep the __StringStorage alive while we're using its
 buffer

(cherry picked from commit 89144300fb8eebe4e9a4b863167ab07580fafb74)
---
 stdlib/public/core/StringCreate.swift | 1 +
 1 file changed, 1 insertion(+)

diff --git a/stdlib/public/core/StringCreate.swift b/stdlib/public/core/StringCreate.swift
index d30fd0d52b67d..4ea7b11eb0573 100644
--- a/stdlib/public/core/StringCreate.swift
+++ b/stdlib/public/core/StringCreate.swift
@@ -120,6 +120,7 @@ extension String {
       )
       return result.asString
     case .error(let initialRange):
+      defer { _fixLifetime(result) }
       //This could be optimized to use excess tail capacity
       return repairUTF8(result.codeUnits, firstKnownBrokenRange: initialRange)
     }

From 09df30a0a9b2d38511de47eae108ace35328e7f8 Mon Sep 17 00:00:00 2001
From: David Smith <david_smith@apple.com>
Date: Tue, 31 Aug 2021 09:14:49 -0700
Subject: [PATCH 2/2] Tests for invalid UTF8 handling

(cherry picked from commit 3f716e3e0f68cfb84ed39ec9df8efe4f85116666)
---
 test/stdlib/StringCreate.swift | 37 ++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/test/stdlib/StringCreate.swift b/test/stdlib/StringCreate.swift
index e31a6788e67d4..183f99c8b052e 100644
--- a/test/stdlib/StringCreate.swift
+++ b/test/stdlib/StringCreate.swift
@@ -57,22 +57,33 @@ if #available(macOS 10.16, iOS 14.0, watchOS 7.0, tvOS 14.0, *) {
       }
       expectEqual(expected, actual)
     }
-
+        
     let validUTF8: [UInt8] = [0x43, 0x61, 0x66, 0xC3, 0xA9]
     let invalidUTF8: [UInt8] = [0x43, 0x61, 0x66, 0xC3]
-
-    let cafe1 = String(unsafeUninitializedCapacity: validUTF8.count) {
-      _ = $0.initialize(from: validUTF8)
-      return validUTF8.count
-    }
-    expectEqual("Café", cafe1)
-
-    let cafe2 = String(unsafeUninitializedCapacity: invalidUTF8.count) {
-      _ = $0.initialize(from: invalidUTF8)
-      return invalidUTF8.count
+    let longerValidUTF8: [UInt8] = [0x21, 0x21, 0x21, 0x21, 0x21, 0x21, 0x21, 0x21, 0x21, 0x21, 0x43, 0x61, 0x66, 0xC3, 0xA9]
+    let longerInvalidUTF8: [UInt8] = [0x21, 0x21, 0x43, 0x61, 0x66, 0xC3, 0x43, 0x61, 0x66, 0xC3, 0x43, 0x61, 0x66, 0xC3]
+    
+    func test(bufferSize: Int, input: [UInt8], expected: String) {
+      let strs = (0..<100).map { _ in
+        String(unsafeUninitializedCapacity: bufferSize) { buffer in
+          _ = buffer.initialize(from: input)
+          return input.count
+        }
+      }
+      for str in strs {
+        expectEqual(expected, str)
+      }
     }
-    expectEqual("Caf�", cafe2)
-
+    
+    test(bufferSize: validUTF8.count, input: validUTF8, expected: "Café")
+    test(bufferSize: invalidUTF8.count, input: invalidUTF8, expected: "Caf�")
+    // Force non-smol strings by using a larger capacity
+    test(bufferSize: 16, input: validUTF8, expected: "Café")
+    test(bufferSize: 16, input: invalidUTF8, expected: "Caf�")
+    test(bufferSize: longerValidUTF8.count, input: longerValidUTF8, expected: "!!!!!!!!!!Café")
+    test(bufferSize: longerInvalidUTF8.count, input: longerInvalidUTF8, expected: "!!Caf�Caf�Caf�")
+    test(bufferSize: 16, input: longerValidUTF8, expected: "!!!!!!!!!!Café")
+    test(bufferSize: 16, input: longerInvalidUTF8, expected: "!!Caf�Caf�Caf�")
     let empty = String(unsafeUninitializedCapacity: 16) { _ in
       // Can't initialize the buffer (e.g. the capacity is too small).
       return 0