darwin.libcxx: (╯°□°）╯︵ ┻━┻ (#398727)

doc/redirects.json

@@ -216,6 +216,12 @@
   "sec-building-packages-with-llvm-using-clang-stdenv": [
     "index.html#sec-building-packages-with-llvm-using-clang-stdenv"
   ],
+  "sec-darwin-libcxx-deployment-targets": [
+    "index.html#sec-darwin-libcxx-deployment-targets"
+  ],
+  "sec-darwin-libcxx-versions": [
+    "index.html#sec-darwin-libcxx-versions"
+  ],
   "sec-functions-library-treefmt": [
     "index.html#sec-functions-library-treefmt"
   ],

doc/release-notes/rl-2511.section.md

@@ -10,6 +10,10 @@
   supported. `pkgsCross.loongarch64-linux-embedded` can be used to build software and systems for these platforms.
 - The official Nix formatter `nixfmt` is now stable and available as `pkgs.nixfmt`, deprecating the temporary `pkgs.nixfmt-rfc-style` attribute. The classic `nixfmt` will stay available for some more time as `pkgs.nixfmt-classic`.
 
+- Darwin has switched to using the system libc++. This was done for improved compatibility and to avoid ODR violations.
+  If a newer C++ library feature is not available on the default deployment target, you will need to increase the deployment target.
+  See the Darwin platform documentation for more details.
+
 ## Backward Incompatibilities {#sec-nixpkgs-release-25.11-incompatibilities}
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->

doc/stdenv/platform-notes.chapter.md

@@ -12,6 +12,9 @@ If it does, you’re done; skip the rest of this.
 - Darwin uses Clang by default instead of GCC. Packages that refer to `$CC` or `cc` should just work in most cases.
   Some packages may hardcode `gcc` or `g++`. You can usually fix that by setting `makeFlags = [ "CC=cc" "CXX=C++" ]`.
   If that does not work, you will have to patch the build scripts yourself to use the correct compiler for Darwin.
+- Darwin uses the system libc++ by default to avoid ODR violations and potential compatibility issues from mixing LLVM libc++ with the system libc++.
+  While mixing the two usually worked, the two implementations are not guaranteed to be ABI compatible and are considered distinct by upstream.
+  See the troubleshooting guide below if you need to use newer C++ library features than those supported by the default deployment target.
 - Darwin needs an SDK to build software.
   The SDK provides a default set of frameworks and libraries to build software, most of which are specific to Darwin.
   There are multiple versions of the SDK packages in Nixpkgs, but one is included by default in the `stdenv`.
@@ -30,6 +33,20 @@ If you run into issues or failures, continue reading below for how to deal with
 
 ### Darwin Issue Troubleshooting {#sec-darwin-troubleshooting}
 
+#### Building a C++ package or library says that certain APIs are unavailable {#sec-darwin-libcxx-versions}
+
+While some newer APIs may be available via headers only, some require using a system libc++ with the required API support.
+When that happens, your build will fail because libc++ makes failure to use the correct deployment target an error.
+To make the newer API available, increase the deployment target to the required version.
+Note that it is possible to use libc++ from LLVM instead of increasing the deployment target, but it is not recommended.
+Doing so can cause problems when multiple libc++ implementations are linked into a binary (e.g., from dependencies).
+
+##### Using a newer deployment target {#sec-darwin-libcxx-deployment-targets}
+
+See below for how to use a newer deployment target.
+For example, `std::print` depends on features that are only available on macOS 13.3 or newer.
+To make them available, set the deployment target to 13.3 using `darwinMinVersionHook`.
+
 #### Package requires a non-default SDK or fails to build due to missing frameworks or symbols {#sec-darwin-troubleshooting-using-sdks}
 
 In some cases, you may have to use a non-default SDK.

pkgs/by-name/ap/apple-sdk/common/process-stubs.nix

@@ -36,21 +36,5 @@ self: super: {
       llvm-readtapi --filetype=tbd-v4 usr/lib/$libSystem~ -o usr/lib/$libSystem
       rm usr/lib/$libSystem~
     done
-
-    # Strip weak C++ symbols to work around `libc++` leakage in system
-    # frameworks for now. These are only present on `x86_64-darwin`, so
-    # it should hopefully be harmless.
-    #
-    # TODO FIXME: This is kind of horrible.
-    while read -r -d "" stub; do
-      printf 'Stripping weak C++ symbols from %s\n' "$stub"
-      llvm-readtapi --filetype=tbd-v5 "$stub" \
-      | jq '
-        (.main_library, .libraries[]?).exported_symbols[]?.data.weak[]? |=
-          select(startswith("__Z") | not)
-      ' > $stub~
-      llvm-readtapi --filetype=tbd-v4 $stub~ -o $stub
-      rm $stub~
-    done < <(find . -name '*.tbd' -print0)
   '';
 }

pkgs/by-name/ap/apple-sdk/metadata/apple-oss-lockfile.json

@@ -711,14 +711,14 @@
       "version": "10063.101.15"
     }
   },
-  "15.2": {
+  "15.5": {
     "CarbonHeaders": {
       "hash": "sha256-nIPXnLr21yVnpBhx9K5q3l/nPARA6JL/dED08MeyhP8=",
       "version": "18.1"
     },
     "CommonCrypto": {
       "hash": "sha256-+qAwL6+s7di9cX/qXtapLkjCFoDuZaSYltRJEG4qekM=",
-      "version": "600033.60.1"
+      "version": "600035"
     },
     "IOAudioFamily": {
       "hash": "sha256-VSk3jvsITJugtL67Qt0m4qJ879i7Fj6B/NGBFVCwpiU=",
@@ -757,16 +757,16 @@
       "version": "261"
     },
     "IOGraphics": {
-      "hash": "sha256-Ag37fd3tZJLXLVq1yzHOCWGOYYfwwTkC8hnvNaTEaWg=",
-      "version": "598"
+      "hash": "sha256-iysZE42mOKZbFxSZBNspaBTCRKEKK38DFGBxZWQxZxI=",
+      "version": "599"
     },
     "IOHIDFamily": {
-      "hash": "sha256-utWAwmn9jss/6fc4flDHXeJR5ZBymO0ZFbDFIFVBnt4=",
-      "version": "2104.61.1"
+      "hash": "sha256-gEYPyjXgQ2ABGufCKPjmzMdNRLxhELkCvOURCokyTO4=",
+      "version": "2115.100.21"
     },
     "IOKitUser": {
-      "hash": "sha256-vfz/kLZlVyoHKOlrNdNrf2HcUOB6bY+mpbCvEEg2sus=",
-      "version": "100140.60.14"
+      "hash": "sha256-p32U+jHfwA/tqnjF4p1BmojghEXK8KxiflW3IHs2iIY=",
+      "version": "100150.120.2"
     },
     "IONetworkingFamily": {
       "hash": "sha256-gZ7Dkk4Iu7AV9K2ioqSeJ1W7bTNxv77bmT18iv3ljLg=",
@@ -777,28 +777,28 @@
       "version": "93"
     },
     "IOStorageFamily": {
-      "hash": "sha256-tjzvlJYVjSTG7oF3AhHgCASKax1fYjOBAxcsrKh/urY=",
-      "version": "317.40.2"
+      "hash": "sha256-/0H0tqWUWkgYigYypucbc7lOCFYDuukwF9fvLEOhwOk=",
+      "version": "323"
     },
     "IOUSBFamily": {
       "hash": "sha256-Z0E3TfKP49toYo1Fo9kElRap8CZ+mVDHy5RIexgJTpA=",
       "version": "630.4.5"
     },
     "Libc": {
-      "hash": "sha256-/J1Oawa+cMbcAlMlpr6ce32KQQp2lMGnfbRi/2Oc1cY=",
-      "version": "1669.60.4"
+      "hash": "sha256-nWDokN0Vr5pUyNGculnDOah9RNgHiWr3S13RSQLmZrc=",
+      "version": "1698.100.8"
     },
     "Libinfo": {
-      "hash": "sha256-D7JMCakQVCQ9j2zUHQSGB8zZcHD6azwYY3bsJU0JfEE=",
-      "version": "592"
+      "hash": "sha256-UI5mGvzZ6BPafGYD6CrNAJAKjeJLB6urAS2lpB6X/Ec=",
+      "version": "597"
     },
     "Libm": {
       "hash": "sha256-p4BndAag9d0XSMYWQ+c4myGv5qXbKx5E1VghudSbpTk=",
       "version": "2026"
     },
     "Libnotify": {
-      "hash": "sha256-XwVB4sYXPLAHDuLv8mxAWlC1ia17V4cf73DEJDDm4ck=",
-      "version": "327.60.1"
+      "hash": "sha256-GDYMVi1034f9empq0YOuumQp/BDJ7phTb0Zl4KTY9xg=",
+      "version": "342"
     },
     "Librpcsvc": {
       "hash": "sha256-UWYdCQ9QsBqwM01bWr+igINAHSdSluB/FrOclC5AjTI=",
@@ -813,80 +813,80 @@
       "version": "146"
     },
     "Security": {
-      "hash": "sha256-sRpFQyMk3x4kRthXpqeAnfQ9dE5RMxiSFUiUKRCneck=",
-      "version": "61439.60.117"
+      "hash": "sha256-ZOrOOCk+hZbzDilzkihpQfsDpzV3Ul4zy6fpFRWUQHw=",
+      "version": "61439.120.27"
     },
     "architecture": {
       "hash": "sha256-PRNUrhzSOrwmxSPkKmV0LV7yEIik65sdkfKdBqcwFhU=",
       "version": "282"
     },
     "configd": {
-      "hash": "sha256-xRaEzq/OOMBi7lvi2bV2/ObN5JJJ5vcFy8DGHLItUWM=",
-      "version": "1351"
+      "hash": "sha256-ZdUq1SrOwB88Lx68ekrA4zeVsLDZz4TAJywNnF+uAzY=",
+      "version": "1351.120.3"
     },
     "copyfile": {
-      "hash": "sha256-Vz1fo4p2b6S8xfyDPu1FNgMkH1aX0tkpXCZkdzkRdq0=",
-      "version": "213.40.2"
+      "hash": "sha256-rLqT6e44W2ohgwUXREmiOyJBYCrV3gRLbtVnbUq60xc=",
+      "version": "221.121.1"
     },
     "dtrace": {
       "hash": "sha256-iNEZyxK3DmEwO3gzrfvCaVZSEuuOMQm5IG/6FodPNdI=",
       "version": "411"
     },
     "dyld": {
-      "hash": "sha256-DDhV7X81nhd3oeJuICEvF8FU43yE/afQ/LYgDNtXswA=",
-      "version": "1241.17"
+      "hash": "sha256-4OOghgUYyMJbsTe96fiWCndTJ1BS94rK9v6Kqn/ooYs=",
+      "version": "1285.19"
     },
     "eap8021x": {
-      "hash": "sha256-2FdEb76KBbCAl2iwly4c1Xstar53O8qgGdN/3WXO23U=",
-      "version": "364"
+      "hash": "sha256-Kx/wwnt108hDm0qQPyTNbZ8KoHkD5m7L4yb5qjSuQjI=",
+      "version": "365.120.2"
     },
     "hfs": {
-      "hash": "sha256-isTLSBDxh12W10I5KY6O6SsygqnOvqJ0TfdWIKSK3pM=",
-      "version": "677.60.1"
+      "hash": "sha256-5/3Ycp3cKqlgAl1kjBmbF5tFlfJYQS5rbrbk4SS66b8=",
+      "version": "683.120.3"
     },
     "launchd": {
       "hash": "sha256-8mW9bnuHmRXCx9py8Wy28C5b2QPICW0rlAps5njYa00=",
       "version": "842.1.4"
     },
     "libclosure": {
-      "hash": "sha256-I0PKQFnoJVRMA7H3yT+inHS0454/FXHhQB6nwmHFvFs=",
-      "version": "95"
+      "hash": "sha256-pvwfcbeEJmTEPdt6/lgVswiabLRG+sMN6VT5FwG7C4Q=",
+      "version": "96"
     },
     "libdispatch": {
-      "hash": "sha256-f2ex/53OFeSR5A0nMapxC6AocqBSweecNtEhp4bWjhE=",
-      "version": "1504.60.7"
+      "hash": "sha256-jTp2DolOOCQPBt1HRotkmPnKgQ2LGgniEqeHoM+vlKg=",
+      "version": "1521.120.4"
     },
     "libmalloc": {
-      "hash": "sha256-Rw/9s7yY3qPtKfDhP+p+0z+aaCsxgwvdUyRG2V1N6D8=",
-      "version": "657.60.21"
+      "hash": "sha256-d9AVHSYTqHDlgctv8Hh4HAYW53MJelj4F8LWPsjrsws=",
+      "version": "715.120.13"
     },
     "libplatform": {
-      "hash": "sha256-o/W1pQ9yGTE8HQlGcggM+XiJbEyqgc/s0uiY3+yBtnA=",
-      "version": "340.60.2"
+      "hash": "sha256-gpijoTMvdkM0PdG8gyIllOJlh/MtTc4ro9ODDAhN6gM=",
+      "version": "349"
     },
     "libpthread": {
-      "hash": "sha256-eYHDAt2wNk7hJZJxsC7Y9w4ASKdexidu613kPo7TAKs=",
-      "version": "535"
+      "hash": "sha256-N+MMXdbthsxauTTfZ5ElUs39dVH+Chn1yyU6pObZpkU=",
+      "version": "536"
     },
     "mDNSResponder": {
-      "hash": "sha256-mDyY/2S4EHbGh02J6VWZVxhNXXZmWGX+NjUjPfMZgZA=",
-      "version": "2559.60.39.0.1"
+      "hash": "sha256-ILx12PRxj/+VqfpCCErJFEJXFI9yzTh4g+FK0UCenIE=",
+      "version": "2600.120.12"
     },
     "objc4": {
-      "hash": "sha256-uBFS5extMQkXAXJfPtPlBYAQpz+zsRHQnEaLpDOcYGM=",
-      "version": "928.3"
+      "hash": "sha256-DMxa25gXjKCkiDnVJ/8SyJUjaBlmBGABg8EfCHcmTj0=",
+      "version": "940.4"
     },
     "ppp": {
       "hash": "sha256-8+QUA79sHf85yvGSPE9qCmGsrZDT3NZnbgZVroJw/Hg=",
       "version": "1016"
     },
     "removefile": {
-      "hash": "sha256-h1jb4DcgDHwi9eiUguc2e5OLP8ZHxCN3B4Myp/DFDBg=",
-      "version": "75"
+      "hash": "sha256-Z5UD0mk/s80CQB0PZWDzSl2JWXmnVmwUvlNb28+hR3k=",
+      "version": "81"
     },
     "xnu": {
-      "hash": "sha256-o8CxHvM2OXiAWJmnFe5ERQYnrNyJ+Bpdb9H0sjd6L10=",
-      "version": "11215.61.5"
+      "hash": "sha256-o4tCuCAIgAYg/Li3wTs12mVWr5C/4vbwu1zi+kJ9d6w=",
+      "version": "11417.121.6"
     }
   }
 }

pkgs/by-name/ap/apple-sdk/metadata/versions.json

@@ -33,10 +33,10 @@
   },
   "15": {
     "urls": [
-      "https://swcdn.apple.com/content/downloads/36/33/072-44426-A_G1AII30AST/ddbss9h6gse6a32rg6luosbrm6vgniu033/CLTools_macOSNMOS_SDK.pkg",
-      "https://web.archive.org/web/20250210234739/https://swcdn.apple.com/content/downloads/36/33/072-44426-A_G1AII30AST/ddbss9h6gse6a32rg6luosbrm6vgniu033/CLTools_macOSNMOS_SDK.pkg"
+      "https://swcdn.apple.com/content/downloads/52/01/082-41241-A_0747ZN8FHV/dectd075r63pppkkzsb75qk61s0lfee22j/CLTools_macOSNMOS_SDK.pkg",
+      "https://web.archive.org/web/20250530132510/https://swcdn.apple.com/content/downloads/52/01/082-41241-A_0747ZN8FHV/dectd075r63pppkkzsb75qk61s0lfee22j/CLTools_macOSNMOS_SDK.pkg"
     ],
-    "version": "15.2",
-    "hash": "sha256-OP5Ah/JnSZ6sD42BD5vGDmikgFzjsfFBmz1hvQD1dOI="
+    "version": "15.5",
+    "hash": "sha256-HBiSJuw1XBUK5R/8Sj65c3rftSEvQl/O9ZZVp/g1Amo="
   }
 }

pkgs/by-name/ov/ovftool/package.nix

@@ -240,7 +240,6 @@ stdenv.mkDerivation (final: {
       done
 
       # Patches for ovftool binary
-      change_args+=(-change /usr/lib/libc++.1.dylib ${stdenv.cc.libcxx}/lib/libc++.1.dylib)
       change_args+=(-change /usr/lib/libiconv.2.dylib ${libiconv}/lib/libiconv.2.dylib)
       change_args+=(-change /usr/lib/libxml2.2.dylib ${libxml2}/lib/libxml2.2.dylib)
       change_args+=(-change /usr/lib/libz.1.dylib ${zlib}/lib/libz.1.dylib)

pkgs/development/compilers/llvm/common/default.nix

@@ -200,6 +200,8 @@ let
       clang =
         if stdenv.targetPlatform.libc == null then
           tools.clangNoLibc
+        else if stdenv.targetPlatform.isDarwin then
+          tools.systemLibcxxClang
         else if stdenv.targetPlatform.useLLVM or false then
           tools.clangUseLLVM
         else if (pkgs.targetPackages.stdenv or args.stdenv).cc.isGNU then
@@ -222,6 +224,15 @@ let
         extraBuildCommands = mkExtraBuildCommands cc;
       };
 
+      # Darwin uses the system libc++ by default. It is set up as its own clang definition so that `libcxxClang`
+      # continues to use the libc++ from LLVM.
+      systemLibcxxClang = wrapCCWith rec {
+        cc = tools.clang-unwrapped;
+        libcxx = darwin.libcxx;
+        extraPackages = [ targetLlvmLibraries.compiler-rt ];
+        extraBuildCommands = mkExtraBuildCommands cc;
+      };
+
       lld = callPackage ./lld {
       };
 
@@ -290,7 +301,8 @@ let
 
       clangWithLibcAndBasicRtAndLibcxx = wrapCCWith rec {
         cc = tools.clang-unwrapped;
-        libcxx = targetLlvmLibraries.libcxx;
+        # This is used to build compiler-rt. Make sure to use the system libc++ on Darwin.
+        libcxx = if stdenv.hostPlatform.isDarwin then darwin.libcxx else targetLlvmLibraries.libcxx;
         bintools = bintools';
         extraPackages = [
           targetLlvmLibraries.compiler-rt-no-libc

pkgs/development/libraries/science/math/libtorch/bin.nix

@@ -24,7 +24,6 @@ let
   device = if cudaSupport then "cuda" else "cpu";
   srcs = import ./binary-hashes.nix version;
   unavailable = throw "libtorch is not available for this platform";
-  libcxx-for-libtorch = if stdenv.hostPlatform.isDarwin then libcxx else (lib.getLib stdenv.cc.cc);
 in
 stdenv.mkDerivation {
   inherit version;
@@ -87,9 +86,6 @@ stdenv.mkDerivation {
         for rpath in $(otool -L $f | grep rpath | awk '{print $1}');do
           install_name_tool -change $rpath $out/lib/$(basename $rpath) $f
         done
-        if otool -L $f | grep /usr/lib/libc++ >& /dev/null; then
-          install_name_tool -change /usr/lib/libc++.1.dylib ${libcxx-for-libtorch.outPath}/lib/libc++.1.0.dylib $f
-        fi
       done
       for f in $out/lib/*.dylib; do
           otool -L $f

pkgs/os-specific/darwin/libcxx/default.nix

@@ -0,0 +1,28 @@
+{
+  # Use the text-based stubs and headers from the latest SDK (currently 15.x). This is safe because
+  # using features that are not available on an older deployment target is a hard error.
+  apple-sdk_15,
+  stdenvNoCC,
+}:
+
+stdenvNoCC.mkDerivation (finalAttrs: {
+  pname = "libcxx";
+  # Keep this in sync with the corresponding LLVM libc++ version
+  # defined as `_LIBCPP_VERSION` in `usr/include/c++/v1/__config`.
+  version = "19.1.2+apple-sdk-${apple-sdk_15.version}";
+  inherit (apple-sdk_15) src;
+
+  dontConfigure = true;
+  dontBuild = true;
+
+  installPhase = ''
+    runHook preInstall
+    mkdir -p "$out/include" "$out/lib"
+    cp -v usr/lib/libc++abi.tbd usr/lib/libc++.1.tbd "$out/lib"
+    ln -s libc++.1.tbd "$out/lib/libc++.tbd"
+    cp -rv usr/include/c++ "$out/include"
+    runHook postInstall
+  '';
+
+  passthru.isLLVM = true;
+})

pkgs/stdenv/adapters.nix

@@ -67,50 +67,6 @@ rec {
       extraBuildInputs = (prev.extraBuildInputs or [ ]) ++ pkgs;
     });
 
-  # Override the libc++ dynamic library used in the stdenv to use the one from the platform’s
-  # default stdenv. This allows building packages and linking dependencies with different
-  # compiler versions while still using the same libc++ implementation for compatibility.
-  #
-  # Note that this adapter still uses the headers from the new stdenv’s libc++. This is necessary
-  # because older compilers may not be able to parse the headers from the default stdenv’s libc++.
-  overrideLibcxx =
-    stdenv:
-    assert stdenv.cc.libcxx != null;
-    assert pkgs.stdenv.cc.libcxx != null;
-    # only unified libcxx / libcxxabi stdenv's are supported
-    assert lib.versionAtLeast pkgs.stdenv.cc.libcxx.version "12";
-    assert lib.versionAtLeast stdenv.cc.libcxx.version "12";
-    let
-      llvmLibcxxVersion = lib.getVersion llvmLibcxx;
-
-      stdenvLibcxx = pkgs.stdenv.cc.libcxx;
-      llvmLibcxx = stdenv.cc.libcxx;
-
-      libcxx =
-        pkgs.runCommand "${stdenvLibcxx.name}-${llvmLibcxxVersion}"
-          {
-            outputs = [
-              "out"
-              "dev"
-            ];
-            isLLVM = true;
-          }
-          ''
-            mkdir -p "$dev/nix-support"
-            ln -s '${stdenvLibcxx}' "$out"
-            echo '${stdenvLibcxx}' > "$dev/nix-support/propagated-build-inputs"
-            ln -s '${lib.getDev llvmLibcxx}/include' "$dev/include"
-          '';
-    in
-    overrideCC stdenv (
-      stdenv.cc.override {
-        inherit libcxx;
-        extraPackages = [
-          pkgs.buildPackages.targetPackages."llvmPackages_${lib.versions.major llvmLibcxxVersion}".compiler-rt
-        ];
-      }
-    );
-
   # Override the setup script of stdenv.  Useful for testing new
   # versions of the setup script without causing a rebuild of
   # everything.

pkgs/stdenv/cross/default.nix

@@ -117,7 +117,7 @@ lib.init bootStages
               then
                 throw "no C compiler provided for this platform"
               else if crossSystem.isDarwin then
-                buildPackages.llvmPackages.libcxxClang
+                buildPackages.llvmPackages.systemLibcxxClang
               else if crossSystem.useLLVM or false then
                 buildPackages.llvmPackages.clang
               else if crossSystem.useZig or false then

pkgs/stdenv/darwin/default.nix

@@ -133,7 +133,14 @@ let
 
             isClang = true;
             inherit (prevStage) libc;
-            inherit (prevStage.llvmPackages) libcxx;
+            # TODO: replace with `darwin.libcxx` once the bootstrap tools no longer have libc++.
+            libcxx =
+              if
+                prevStage.darwin.libcxx == null || name == "bootstrap-stage1" || name == "bootstrap-stage-xclang"
+              then
+                prevStage.llvmPackages.libcxx
+              else
+                prevStage.darwin.libcxx;
 
             inherit lib;
             inherit (prevStage) coreutils gnugrep;
@@ -298,6 +305,7 @@ let
 
   # LLVM tools packages are staged separately (xclang, stage3) from LLVM libs (xclang).
   llvmLibrariesPackages = prevStage: { inherit (prevStage.llvmPackages) compiler-rt libcxx; };
+  llvmLibrariesDarwinDepsNoCC = prevStage: { inherit (prevStage.darwin) libcxx; };
   llvmLibrariesDeps = _: { };
 
   llvmToolsPackages = prevStage: {
@@ -365,6 +373,7 @@ assert bootstrapTools.passthru.isFromBootstrapFiles or false; # sanity check
       darwin = {
         binutils = null;
         binutils-unwrapped = null;
+        libcxx = null;
         libSystem = null;
         sigtool = null;
       };
@@ -986,7 +995,7 @@ assert bootstrapTools.passthru.isFromBootstrapFiles or false; # sanity check
                   _: _:
                   llvmToolsPackages prevStage
                   // {
-                    libcxxClang = super.wrapCCWith rec {
+                    systemLibcxxClang = super.wrapCCWith rec {
                       nativeTools = false;
                       nativeLibc = false;
 
@@ -1008,7 +1017,7 @@ assert bootstrapTools.passthru.isFromBootstrapFiles or false; # sanity check
 
                       isClang = true;
                       libc = self.darwin.libSystem;
-                      inherit (self.llvmPackages) libcxx;
+                      inherit (self.darwin) libcxx;
 
                       inherit lib;
                       inherit (self)
@@ -1160,6 +1169,7 @@ assert bootstrapTools.passthru.isFromBootstrapFiles or false; # sanity check
           ]
           ++ lib.optionals localSystem.isx86_64 [ prevStage.darwin.Csu ]
           ++ (with prevStage.darwin; [
+            libcxx
             libiconv.out
             libresolv.out
             libsbuf.out
@@ -1172,8 +1182,6 @@ assert bootstrapTools.passthru.isFromBootstrapFiles or false; # sanity check
             (lib.getLib clang-unwrapped)
             compiler-rt
             compiler-rt.dev
-            libcxx
-            libcxx.dev
             lld
             llvm
             llvm.lib
@@ -1268,7 +1276,6 @@ assert bootstrapTools.passthru.isFromBootstrapFiles or false; # sanity check
 
     assert isBuiltByNixpkgsCompiler prevStage.llvmPackages.clang-unwrapped;
     assert isBuiltByNixpkgsCompiler prevStage.llvmPackages.libllvm;
-    assert isBuiltByNixpkgsCompiler prevStage.llvmPackages.libcxx;
     assert isBuiltByNixpkgsCompiler prevStage.llvmPackages.compiler-rt;
 
     # Make sure these evaluate since they were disabled explicitly in the bootstrap.

pkgs/top-level/aliases.nix

@@ -1914,6 +1914,7 @@ mapAliases {
   oraclejdk11 = throw "All Oracle JDKs and JREs were dropped due to being unmaintained and heavily insecure. OpenJDK provides compatible replacements for JDKs and JREs."; # Added 2024-11-01
   OSCAR = oscar; # Added 2024-06-12
   osxfuse = throw "'osxfuse' has been renamed to/replaced by 'macfuse-stubs'"; # Converted to throw 2024-10-17
+  overrideLibcxx = "overrideLibcxx has beeen removed, as it was no longer used and Darwin now uses libc++ from the latest SDK; see the Nixpkgs 25.11 release notes for details"; # Added 2025-09-15
   overrideSDK = "overrideSDK has been removed as it was a legacy compatibility stub. See <https://nixos.org/manual/nixpkgs/stable/#sec-darwin-legacy-frameworks-overrides> for migration instructions"; # Added 2025-08-04
   ovn-lts = throw "ovn-lts has been removed. Please use the latest version available under ovn"; # Added 2024-08-24
   oxygen-icons5 = throw ''

pkgs/top-level/darwin-packages.nix

@@ -101,6 +101,8 @@ makeScopeWithSplicing' {
 
         libunwind = callPackage ../os-specific/darwin/libunwind { };
 
+        libcxx = callPackage ../os-specific/darwin/libcxx { };
+
         sigtool = callPackage ../os-specific/darwin/sigtool { };
 
         signingUtils = callPackage ../os-specific/darwin/signing-utils { };