Hide all ICU public C++ Symbols (#34)

* Hide all ICU public C++ Symbols

**Rationale:** When FoundationInternationalization tests are executed, we effectively load two ICU instances into memory: 1) The system ICU loaded by XCTest via system Foundation; 2) The package ICU SwiftFoundation utilizes.

These two ICUs cause symbol collisions for dyld due to the fact that all public C++ symbols share a global namespace and coalesce across all loaded dylibs. Consequently, we encounter sporadic test failures in SwiftFoundation as dyld arbitrarily selects ICU symbols and occasionally chooses the system one.

To address this issue, we resolved to hide all C++ APIs, ensuring they are not weakly referenced and potentially bound to the system ICU implementation. This solution proves effective for SwiftFoundation, as it does not actually utilize the C++ APIs.

* Use U_CAPI for uspoof_getInclusionUnicodeSet and uspoof_getRecommendedUnicodeSet

Author: iCharlesHu

icuSources/i18n/uspoof.cpp

@@ -781,13 +781,13 @@ uspoof_getRecommendedSet(UErrorCode *status) {
     return gRecommendedSet->toUSet();
 }
 
-U_I18N_API const UnicodeSet * U_EXPORT2
+U_CAPI const UnicodeSet * U_EXPORT2
 uspoof_getInclusionUnicodeSet(UErrorCode *status) {
     umtx_initOnce(gSpoofInitStaticsOnce, &initializeStatics, *status);
     return gInclusionSet;
 }
 
-U_I18N_API const UnicodeSet * U_EXPORT2
+U_CAPI const UnicodeSet * U_EXPORT2
 uspoof_getRecommendedUnicodeSet(UErrorCode *status) {
     umtx_initOnce(gSpoofInitStaticsOnce, &initializeStatics, *status);
     return gRecommendedSet;

icuSources/include/_foundation_unicode/utypes.h

@@ -354,13 +354,31 @@ typedef double UDate;
 #endif
 
 #if defined(U_COMBINED_IMPLEMENTATION)
-#define U_DATA_API     U_EXPORT
-#define U_COMMON_API   U_EXPORT
-#define U_I18N_API     U_EXPORT
-#define U_LAYOUT_API   U_EXPORT
-#define U_LAYOUTEX_API U_EXPORT
-#define U_IO_API       U_EXPORT
-#define U_TOOLUTIL_API U_EXPORT
+// SwiftFoundationICU Changes: hide all C++ public symbols
+// Rationale: When FoundationInternationalization tests are executed,
+// we effectively load two ICU instances into memory:
+//
+// 1) The system ICU loaded by XCTest via system Foundation;
+// 2) The package ICU SwiftFoundation utilizes.
+//
+// These two ICUs cause symbol collisions for dyld due to the fact that
+// all public C++ symbols share a global namespace and coalesce across all loaded dylibs.
+// Consequently, we encounter sporadic test failures in SwiftFoundation as dyld
+// arbitrarily selects ICU symbols and occasionally chooses the system one.
+//
+// To address this issue, we resolved to hide all C++ APIs,
+// ensuring they are not weakly referenced and potentially bound to
+// the system ICU implementation.
+//
+// This solution proves effective for SwiftFoundation,
+// as it does not actually utilize the C++ APIs.
+#define U_DATA_API     __attribute__((visibility("hidden")))
+#define U_COMMON_API   __attribute__((visibility("hidden")))
+#define U_I18N_API     __attribute__((visibility("hidden")))
+#define U_LAYOUT_API   __attribute__((visibility("hidden")))
+#define U_LAYOUTEX_API __attribute__((visibility("hidden")))
+#define U_IO_API       __attribute__((visibility("hidden")))
+#define U_TOOLUTIL_API __attribute__((visibility("hidden")))
 #elif defined(U_STATIC_IMPLEMENTATION)
 #define U_DATA_API
 #define U_COMMON_API