fix(3p/nix): Properly configure SANDBOX_SHELL

point the SANDBOX_SHELL macro at the actual path to busybox on the build
machine, or allow it to be configured at build-time with a cmake option.

Change-Id: I044a1315ba9baa3bc9ceddf29f36d14f9f9ccd96
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1632
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

third_party/default.nix

@@ -47,6 +47,7 @@ let
       buildGoPackage
       buildPackages
       buildkite-agent
+      busybox
       bzip2
       c-ares
       cacert

third_party/nix/CMakeLists.txt

@@ -40,6 +40,15 @@ if (CLANG_TIDY_PATH)
   endif()
 endif()
 
+if (NOT SANDBOX_SHELL)
+  find_program(BUSYBOX busybox)
+  if (BUSYBOX)
+    set(SANDBOX_SHELL "${BUSYBOX}")
+  else()
+    message(FATAL_ERROR "Could not find busybox and SANDBOX_SHELL is not set")
+  endif()
+endif()
+
 # generate a configuration file (autoheader-style) to configure
 # certain symbols that Nix depends on.
 configure_file(config.h.in nix_config.h @ONLY)

third_party/nix/config.h.in

@@ -23,7 +23,7 @@
 #define NIX_LIBEXEC_DIR "@CMAKE_INSTALL_FULL_LIBEXECDIR@"
 #define NIX_BIN_DIR "@CMAKE_INSTALL_FULL_BINDIR@"
 #define NIX_MAN_DIR "@CMAKE_INSTALL_FULL_MANDIR@"
-#define SANDBOX_SHELL "/nix/store/zq8biwi5mj2lrn68kx0lk0fkpbqypyxd-busybox-1.31.1-x86_64-unknown-linux-musl/bin/busybox"
+#define SANDBOX_SHELL "@SANDBOX_SHELL@"
 
 // Defines used only in tests (e.g. to access data)
 #define NIX_SRC_DIR "@CMAKE_SOURCE_DIR@"

third_party/nix/default.nix

@@ -30,6 +30,14 @@ let
       --plugin=protoc-gen-grpc=${pkgs.grpc}/bin/grpc_cpp_plugin --grpc_out=$out/libproto \
       $PROTO_SRCS/*.proto
   '';
+
+  # Derivation for busybox that just has the `busybox` binary in bin/, not all
+  # the symlinks, so cmake can find it
+  busybox = pkgs.runCommand "busybox" {} ''
+    mkdir -p $out/bin
+    cp ${pkgs.busybox}/bin/busybox $out/bin
+  '';
+
 in lib.fix (self: pkgs.llvmPackages.libcxxStdenv.mkDerivation {
   pname = "tvix";
   version = "2.3.4";
@@ -87,7 +95,8 @@ in lib.fix (self: pkgs.llvmPackages.libcxxStdenv.mkDerivation {
       -DCMAKE_BUILD_TYPE=RelWithDebInfo \
       -DCMAKE_FIND_USE_SYSTEM_PACKAGE_REGISTRY=OFF \
       -DCMAKE_FIND_USE_PACKAGE_REGISTRY=OFF \
-      -DCMAKE_EXPORT_NO_PACKAGE_REGISTRY=ON
+      -DCMAKE_EXPORT_NO_PACKAGE_REGISTRY=ON \
+      -DSANDBOX_SHELL=${pkgs.busybox}/bin/busybox
   '';
 
   installCheckPhase = ''
@@ -114,6 +123,8 @@ in lib.fix (self: pkgs.llvmPackages.libcxxStdenv.mkDerivation {
   # Work around broken system header include flags in the cxx toolchain.
   LIBCXX_INCLUDE = "${pkgs.llvmPackages.libcxx}/include/c++/v1";
 
+  SANDBOX_SHELL="${pkgs.busybox}/bin/busybox";
+
   # Install the various symlinks to the Nix binary which users expect
   # to exist.
   postInstall = ''