From 0d4b1c1cb93cc49d7b9cf8d750efadcfd20dea45 Mon Sep 17 00:00:00 2001
From: Frank Tang <ftang@chromium.org>
Date: Mon, 20 Jul 2020 22:35:31 +0000
Subject: [PATCH] ICU-21160 Fix the length return by preflight

See #1178
---
 icu4c/source/common/locdispnames.cpp | 24 +++++++++++++++---------
 icu4c/source/test/cintltst/cloctst.c | 21 +++++++++++++++++++++
 icu4c/source/test/cintltst/cloctst.h |  2 ++
 3 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/icu4c/source/common/locdispnames.cpp b/icu4c/source/common/locdispnames.cpp
index 3f056c35e58..0255d30da8a 100644
--- a/icu4c/source/common/locdispnames.cpp
+++ b/icu4c/source/common/locdispnames.cpp
@@ -406,17 +406,23 @@ uloc_getDisplayScript(const char* locale,
                       UChar *dest, int32_t destCapacity,
                       UErrorCode *pErrorCode)
 {
-	UErrorCode err = U_ZERO_ERROR;
-	int32_t res = _getDisplayNameForComponent(locale, displayLocale, dest, destCapacity,
+    UErrorCode err = U_ZERO_ERROR;
+    int32_t res = _getDisplayNameForComponent(locale, displayLocale, dest, destCapacity,
                 uloc_getScript, _kScriptsStandAlone, &err);
-	
-	if ( err == U_USING_DEFAULT_WARNING ) {
+
+    if (destCapacity == 0 && err == U_BUFFER_OVERFLOW_ERROR) {
+        // For preflight, return the max of the value and the fallback.
+        int32_t fallback_res = _getDisplayNameForComponent(locale, displayLocale, dest, destCapacity,
+                                                           uloc_getScript, _kScripts, pErrorCode);
+        return (fallback_res > res) ? fallback_res : res;
+    }
+    if ( err == U_USING_DEFAULT_WARNING ) {
         return _getDisplayNameForComponent(locale, displayLocale, dest, destCapacity,
-                    uloc_getScript, _kScripts, pErrorCode);
-	} else {
-		*pErrorCode = err;
-		return res;
-	}
+                                           uloc_getScript, _kScripts, pErrorCode);
+    } else {
+        *pErrorCode = err;
+        return res;
+    }
 }
 
 static int32_t
diff --git a/icu4c/source/test/cintltst/cloctst.c b/icu4c/source/test/cintltst/cloctst.c
index 71d62c19fa2..2dc4a08cd38 100644
--- a/icu4c/source/test/cintltst/cloctst.c
+++ b/icu4c/source/test/cintltst/cloctst.c
@@ -217,6 +217,7 @@ void addLocaleTest(TestNode** root)
     TESTCASE(TestPrefixes);
     TESTCASE(TestSimpleResourceInfo);
     TESTCASE(TestDisplayNames);
+    TESTCASE(TestGetDisplayScriptPreFlighting21160);
     TESTCASE(TestGetAvailableLocales);
     TESTCASE(TestGetAvailableLocalesByType);
     TESTCASE(TestDataDirectory);
@@ -808,6 +809,26 @@ static void TestDisplayNames()
     }
 }
 
+/**
+ * ICU-21160 test the pre-flighting call to uloc_getDisplayScript returns the actual length needed
+ * for the result buffer.
+ */
+static void TestGetDisplayScriptPreFlighting21160()
+{
+    const char* locale = "und-Latn";
+    const char* inlocale = "de";
+
+    UErrorCode ec = U_ZERO_ERROR;
+    UChar* result = NULL;
+    int32_t length = uloc_getDisplayScript(locale, inlocale, NULL, 0, &ec) + 1;
+    ec = U_ZERO_ERROR;
+    result=(UChar*)malloc(sizeof(UChar) * length);
+    length = uloc_getDisplayScript(locale, inlocale, result, length, &ec);
+    if (U_FAILURE(ec)) {
+        log_err("uloc_getDisplayScript length %d returned error %s", length, u_errorName(ec));
+    }
+    free(result);
+}
 
 /* test for uloc_getAvialable()  and uloc_countAvilable()*/
 static void TestGetAvailableLocales()
diff --git a/icu4c/source/test/cintltst/cloctst.h b/icu4c/source/test/cintltst/cloctst.h
index be61de10ba8..3aaba109178 100644
--- a/icu4c/source/test/cintltst/cloctst.h
+++ b/icu4c/source/test/cintltst/cloctst.h
@@ -33,6 +33,8 @@ static void TestSimpleResourceInfo(void);
  * Use Locale to access Resource file display names and compare against expected values
  **/
 static  void TestDisplayNames(void);
+static  void TestGetDisplayScriptPreFlighting21160(void);
+
 /**
  * Test getAvailableLocales
  **/