Merge pull request NixOS#12686 from NixOS/mergify/bp/2.27-maintenance/pr-12570

Fix macos sandbox issue (backport NixOS#12570)

Author: mergify[bot]

src/libstore/unix/build/local-derivation-goal.cc

@@ -2144,7 +2144,18 @@ void LocalDerivationGoal::runChild()
                without file-write* allowed, access() incorrectly returns EPERM
              */
             sandboxProfile += "(allow file-read* file-write* process-exec\n";
+
+            // We create multiple allow lists, to avoid exceeding a limit in the darwin sandbox interpreter.
+            // See https://github.com/NixOS/nix/issues/4119
+            // We split our allow groups approximately at half the actual limit, 1 << 16
+            const int breakpoint = sandboxProfile.length() + (1 << 14);
             for (auto & i : pathsInChroot) {
+
+                if (sandboxProfile.length() >= breakpoint) {
+                    debug("Sandbox break: %d %d", sandboxProfile.length(), breakpoint);
+                    sandboxProfile += ")\n(allow file-read* file-write* process-exec\n";
+                }
+
                 if (i.first != i.second.source)
                     throw Error(
                         "can't map '%1%' to '%2%': mismatched impure paths not supported on Darwin",