icu: make darwin.ICU the default on Darwin (#360922)

pkgs/os-specific/darwin/apple-source-releases/ICU/package.nix

···
   fixDarwinDylibNames,
   mkAppleDerivation,
   python3,
+  stdenv, # Necessary for compatibility with python3Packages.tensorflow, which tries to override the stdenv
   testers,
 }:
 
···
     sourceRoot = "source/icu/icu4c/source";
 
     patches = [
+      # Apple defaults to `uint16_t` for compatibility with building one of their private frameworks,
+      # but nixpkgs needs `char16_t` for compatibility with packages that expect upstream ICU with `char16_t`.
+      # According to `unicode/umachine.h`, these types are bit-compatible but distinct in C++.
+      ./patches/define-uchar-as-char16_t.patch
+      # Enable the C++ API by default to match the upstream ICU packaging in nixpkgs
+      ./patches/enable-cxx-api-by-default.patch
       # Skip MessageFormatTest test, which is known to crash sometimes and should be suppressed if it does.
       ./patches/suppress-icu-check-crash.patch
     ];

pkgs/os-specific/darwin/apple-source-releases/ICU/patches/define-uchar-as-char16_t.patch

···
+diff --git a/icu/icu4c/source/common/unicode/umachine.h b/icu/icu4c/source/common/unicode/umachine.h
+index 9483031569..e451ad7c02 100644
+--- a/common/unicode/umachine.h
++++ b/common/unicode/umachine.h
+@@ -387,39 +387,6 @@
+  * @stable ICU 4.4
+  */
+ 
+-#if APPLE_ICU_CHANGES
+-// rdar://121241618 (StarlightE: VideosUI-883.40.54#24 has failed to build in install; cannot initialize a variable of type 'const UChar *' (aka 'const char16_t)
+-#if 0
+- // #if 1 is normal (Apple uses 0 to force us to still use uint16_t). UChar defaults to char16_t in C++.
+- // For configuration testing of UChar=uint16_t temporarily change this to #if 0.
+- // The intltest Makefile #defines UCHAR_TYPE=char16_t,
+- // so we only #define it to uint16_t if it is undefined so far.
+-#elif !defined(UCHAR_TYPE)
+-#   define UCHAR_TYPE uint16_t
+-#endif
+-
+-#if defined(U_COMBINED_IMPLEMENTATION) || defined(U_COMMON_IMPLEMENTATION) || \
+-        defined(U_I18N_IMPLEMENTATION) || defined(U_IO_IMPLEMENTATION) || \
+-        defined (U_TOOLUTIL_IMPLEMENTATION)
+-    // Inside the ICU library code, never configurable.
+-    typedef char16_t UChar;
+-#elif defined(T_CTEST_IMPLEMENTATION)
+-    // internally to ctestfw, we want to use char16_t in C++ and uint_16 in C
+-    #if U_CPLUSPLUS_VERSION != 0
+-        typedef char16_t UChar;  // C++
+-    #else
+-        typedef uint16_t UChar;  // C
+-    #endif
+-#elif defined(UCHAR_TYPE)
+-    typedef UCHAR_TYPE UChar;
+-#elif U_CPLUSPLUS_VERSION != 0
+-    typedef char16_t UChar;  // C++
+-#else
+-    typedef uint16_t UChar;  // C
+-#endif
+-
+-#else
+-
+ #if 1
+     // #if 1 is normal. UChar defaults to char16_t in C++.
+     // For configuration testing of UChar=uint16_t temporarily change this to #if 0.
+@@ -441,8 +408,6 @@
+     typedef uint16_t UChar;  // C
+ #endif
+ 
+-#endif // APPLE_ICU_CHANGES
+-
+ /**
+  * \var OldUChar
+  * Default ICU 58 definition of UChar.

pkgs/os-specific/darwin/apple-source-releases/ICU/patches/enable-cxx-api-by-default.patch

···
+diff --git a/icu/icu4c/source/common/unicode/utypes.h b/icu/icu4c/source/common/unicode/utypes.h
+index a3e0ec911c..e361c658ef 100644
+--- a/common/unicode/utypes.h
++++ b/common/unicode/utypes.h
+@@ -66,20 +66,6 @@
+  * \def U_SHOW_CPLUSPLUS_API
+  * @internal
+  */
+-#if APPLE_ICU_CHANGES
+-// rdar://60884991 #58 Replace installsrc patching with changes directly in header files
+-// Apple modifies the default to be 0, not 1
+-#ifdef __cplusplus
+-#   ifndef U_SHOW_CPLUSPLUS_API
+-#       define U_SHOW_CPLUSPLUS_API 0
+-#   endif
+-#else
+-#   undef U_SHOW_CPLUSPLUS_API
+-#   define U_SHOW_CPLUSPLUS_API 0
+-#endif
+-
+-#else
+-
+ #ifdef __cplusplus
+ #   ifndef U_SHOW_CPLUSPLUS_API
+ #       define U_SHOW_CPLUSPLUS_API 1
+@@ -89,28 +75,6 @@
+ #   define U_SHOW_CPLUSPLUS_API 0
+ #endif
+ 
+-#endif // APPLE_ICU_CHANGES
+-
+-
+-#if APPLE_ICU_CHANGES
+-// rdar://30624081 64b8ed9b89.. Add #if U_SHOW_CPLUSPLUS_API..#endif around C++ interfaces that don’t have it
+-// rdar://24075048 0f5f76d43c.. update ICU for AAS to use VS2015, remove old ICU 4.0 shims, fix build issues
+-/* 
+- * Apple-specific warning if U_SHOW_CPLUSPLUS_API set and the compile
+- * is not for a build of ICU itself (ICU_DATA_DIR is always defined
+- * for ICU builds, and is unlikely to be defined for client builds).
+- * Windows VSC compliler does not like #warning, skip for it.
+- */
+-#if U_SHOW_CPLUSPLUS_API
+-#ifndef ICU_DATA_DIR
+-#if U_PLATFORM!=U_PF_WINDOWS
+-#warning Do not set U_SHOW_CPLUSPLUS_API for code that ships with the OS, it is only for local tools.
+-#warning ICU C++ functionality may not be used by any OS client, it is not binary compatible across updates.
+-#endif
+-#endif
+-#endif
+-#endif // APPLE_ICU_CHANGES
+-
+ /** @{ API visibility control */
+ 
+ /**

pkgs/top-level/all-packages.nix

···
     icu76
   ;
 
-  icu = icu74;
+  # Use Apple’s fork of ICU by default, which provides additional APIs that are not present in upstream ICU.
+  #
+  # `icuReal` is provided in case the upstream icu package is needed on Darwin instead of the fork.
+  # Note that the versioned icu packages always correspond to the upstream versions.
+  icuReal = icu74;
+  icu = if stdenv.hostPlatform.isDarwin then darwin.ICU else icuReal;
 
   idasen = with python3Packages; toPythonApplication idasen;