From 53adb4bca86b75c4a77b60d9081e2e5ea4501ffa Mon Sep 17 00:00:00 2001
From: Frank Tang <ftang@chromium.org>
Date: Wed, 26 Feb 2025 18:53:57 -0800
Subject: [PATCH] ICU-23060 Fix TestLargeAppend

Correct the test based on the kMaxCapacity
setToBogus on error
---
 icu4c/source/common/unistr.cpp          |  2 ++
 icu4c/source/test/intltest/ustrtest.cpp | 19 +++++++++++++------
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/icu4c/source/common/unistr.cpp b/icu4c/source/common/unistr.cpp
index 7b48addbe85..4e29bad1d3b 100644
--- a/icu4c/source/common/unistr.cpp
+++ b/icu4c/source/common/unistr.cpp
@@ -1946,9 +1946,11 @@ UnicodeString::cloneArrayIfNeeded(int32_t newCapacity,
     } else if(newCapacity <= US_STACKBUF_SIZE && growCapacity > US_STACKBUF_SIZE) {
       growCapacity = US_STACKBUF_SIZE;
     } else if(newCapacity > growCapacity) {
+      setToBogus();
       return false;  // bad inputs
     }
     if(growCapacity > kMaxCapacity) {
+      setToBogus();
       return false;
     }
 
diff --git a/icu4c/source/test/intltest/ustrtest.cpp b/icu4c/source/test/intltest/ustrtest.cpp
index 31cb6519051..f0466982cff 100644
--- a/icu4c/source/test/intltest/ustrtest.cpp
+++ b/icu4c/source/test/intltest/ustrtest.cpp
@@ -2392,15 +2392,17 @@ void UnicodeStringTest::TestLargeAppend() {
     }
     dest.remove();
     total = 0;
+    // Copy kMaxCapacity from common/unistr.cpp
+    const int32_t kMaxCapacity = 0x7ffffff5;
     for (int32_t i = 0; i < 16; i++) {
         dest.append(str);
         total += len;
-        if (total + len <= INT32_MAX) {
+        if (total + len <= kMaxCapacity) {
             assertFalse("dest is not bogus", dest.isBogus());
-        } else if (total <= INT32_MAX) {
+        } else if (total <= kMaxCapacity) {
             // Check that a string of exactly the maximum size works
             UnicodeString str2;
-            int32_t remain = static_cast<int32_t>(INT32_MAX - total);
+            int32_t remain = static_cast<int32_t>(kMaxCapacity - total);
             char16_t *buf2 = str2.getBuffer(remain);
             if (buf2 == nullptr) {
                 // if somehow memory allocation fail, return the test
@@ -2410,14 +2412,19 @@ void UnicodeStringTest::TestLargeAppend() {
             str2.releaseBuffer(remain);
             dest.append(str2);
             total += remain;
-            assertEquals("When a string of exactly the maximum size works", static_cast<int64_t>(INT32_MAX), total);
-            assertEquals("When a string of exactly the maximum size works", INT32_MAX, dest.length());
+            assertEquals("When a string of exactly the maximum size works", static_cast<int64_t>(kMaxCapacity), total);
+            assertEquals("When a string of exactly the maximum size works", kMaxCapacity, dest.length());
             assertFalse("dest is not bogus", dest.isBogus());
 
-            // Check that a string size+1 goes bogus
+            // Check that a string size+1 does not go bogus (one more byte reserved for NUL)
             str2.truncate(1);
             dest.append(str2);
             total++;
+            assertFalse("dest should be not bogus", dest.isBogus());
+            // Check that a string size+2 goes bogus (beyond the byte reserved
+            // for NUL)
+            dest.append(str2);
+            total++;
             assertTrue("dest should be bogus", dest.isBogus());
         } else {
             assertTrue("dest should be bogus", dest.isBogus());