[Backport staging-24.11] xcbuild: find system toolchain on macOS Sonoma and earlier (#357327)

diff --git a/Libraries/xcsdk/Tools/xcrun.cpp b/Libraries/xcsdk/Tools/xcrun.cpp

index 9d6d4576d7..73aabc3d42 100644

--- a/Libraries/xcsdk/Tools/xcrun.cpp

+++ b/Libraries/xcsdk/Tools/xcrun.cpp

@@ -23,10 +23,14 @@

diff -Naur a/Libraries/xcsdk/Tools/xcrun.cpp b/Libraries/xcsdk/Tools/xcrun.cpp

--- a/Libraries/xcsdk/Tools/xcrun.cpp	1970-01-01 09:00:01

+++ b/Libraries/xcsdk/Tools/xcrun.cpp	2024-11-19 01:44:38

@@ -23,10 +23,19 @@

 #include <process/DefaultUser.h>

 #include <pbxsetting/Type.h>

 using libutil::Filesystem;

 using libutil::FSUtil;

+#define SYSTEM_DEVELOPER_DIR "/private/var/select/developer_dir"

+namespace {

+  const std::vector<const std::string> kSystemDeveloperDirs = {

+    "/private/var/select/developer_dir",

+    "/private/var/db/xcode_select_link"

+  };

+}

+

 class Options {

 private:

     ext::optional<bool>        _help;

@@ -398,6 +402,8 @@

@@ -398,6 +407,8 @@

             fprintf(stderr, "\n");

         }

         /*

          * Collect search paths for the tool.

          * Can be in toolchains, target (if one is provided), developer root,

@@ -408,10 +414,42 @@

@@ -408,10 +419,46 @@

         executablePaths.insert(executablePaths.end(), defaultExecutablePaths.begin(), defaultExecutablePaths.end());

         /*

+             * Fixes https://github.com/NixOS/nixpkgs/issues/353875.

+             */

+            std::vector<std::string> toolchainPaths = { };

+            if (executablePaths.size() < originalSize && filesystem->exists(SYSTEM_DEVELOPER_DIR)) {

+                auto linkTarget = filesystem->readSymbolicLinkCanonical(SYSTEM_DEVELOPER_DIR);

+            if (executablePaths.size() < originalSize) {

+                for (const auto& dir : kSystemDeveloperDirs) {

+                    if (filesystem->exists(dir)) {

+                        auto linkTarget = filesystem->readSymbolicLinkCanonical(dir);

+                        if (linkTarget) {

+                            auto usrBinPath = FSUtil::NormalizePath(*linkTarget + "/usr/bin");

+                            if (filesystem->exists(usrBinPath)) {

+                            }

+                        }

+                    }

+                }

+            }

+            executable = filesystem->findExecutable(*options.tool(), toolchainPaths);

+        }

+

             fprintf(stderr, "error: tool '%s' not found\n", options.tool()->c_str());

             return 1;

         }

@@ -428,8 +466,6 @@

@@ -427,8 +474,6 @@

             return 0;

         } else {

             /* Run is the default. */

-            std::unordered_map<std::string, std::string> environment = processContext->environmentVariables();

-

-            std::unordered_map<std::string, std::string> environment = processContext->environmentVariables();

             if (target != nullptr) {

                 /*

                  * Update effective environment to include the target path.