protobuf: fix protoc used when cross-compiling

pkgs/applications/blockchains/monero-cli/default.nix

@@ -23,7 +23,7 @@
   trezorSupport ? true,
   hidapi,
   libusb1,
-  protobuf_21,
+  protobuf,
   udev,
 }:
 
@@ -96,7 +96,7 @@ stdenv.mkDerivation rec {
       python3
       hidapi
       libusb1
-      protobuf_21
+      protobuf
     ]
     ++ lib.optionals (trezorSupport && stdenv.hostPlatform.isLinux) [ udev ];
 
@@ -138,5 +138,7 @@ stdenv.mkDerivation rec {
       rnhmjoj
     ];
     mainProgram = "monero-wallet-cli";
+    # internal build tool generate_translations_header is tricky to compile for the build platform
+    broken = !stdenv.buildPlatform.canExecute stdenv.hostPlatform;
   };
 }

pkgs/applications/blockchains/monero-gui/default.nix

@@ -30,7 +30,7 @@
   trezorSupport ? true,
   hidapi,
   libusb1,
-  protobuf_21,
+  protobuf,
   python3,
   udev,
 }:
@@ -77,7 +77,7 @@ stdenv.mkDerivation rec {
     ++ lib.optionals trezorSupport [
       hidapi
       libusb1
-      protobuf_21
+      protobuf
       python3
     ]
     ++ lib.optionals (trezorSupport && stdenv.hostPlatform.isLinux) [

pkgs/development/libraries/opencv/4.x.nix

@@ -12,7 +12,7 @@
 , glib
 , glog
 , gflags
-, protobuf_21
+, protobuf_29
 , config
 , ocl-icd
 , buildPackages
@@ -308,7 +308,7 @@ effectiveStdenv.mkDerivation {
     glib
     glog
     pcre2
-    protobuf_21
+    protobuf_29
     zlib
   ] ++ optionals enablePython [
     pythonPackages.python
@@ -419,7 +419,6 @@ effectiveStdenv.mkDerivation {
     (cmakeBool "OPENCV_GENERATE_PKGCONFIG" true)
     (cmakeBool "WITH_OPENMP" true)
     (cmakeBool "BUILD_PROTOBUF" false)
-    (cmakeOptionType "path" "Protobuf_PROTOC_EXECUTABLE" (getExe buildPackages.protobuf_21))
     (cmakeBool "PROTOBUF_UPDATE_FILES" true)
     (cmakeBool "OPENCV_ENABLE_NONFREE" enableUnfree)
     (cmakeBool "BUILD_TESTS" runAccuracyTests)

pkgs/development/libraries/protobuf/generic.nix

@@ -13,6 +13,7 @@
   zlib,
   version,
   hash,
+  replaceVars,
   versionCheckHook,
 
   # downstream dependencies
@@ -36,9 +37,9 @@ stdenv.mkDerivation (finalAttrs: {
     inherit hash;
   };
 
-  postPatch = lib.optionalString stdenv.hostPlatform.isDarwin ''
+  postPatch = lib.optionalString (stdenv.hostPlatform.isDarwin && lib.versionOlder version "29") ''
     substituteInPlace src/google/protobuf/testing/googletest.cc \
-      --replace 'tmpnam(b)' '"'$TMPDIR'/foo"'
+      --replace-fail 'tmpnam(b)' '"'$TMPDIR'/foo"'
   '';
 
   patches = lib.optionals (lib.versionOlder version "22") [
@@ -50,15 +51,17 @@ stdenv.mkDerivation (finalAttrs: {
     })
   ];
 
-  nativeBuildInputs =
-    [
-      cmake
-    ]
-    ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
-      # protoc of the same version must be available for build. For non-cross builds, it's able to
-      # re-use the executable generated as part of the build
+  # hook to provide the path to protoc executable, used at build time
+  build_protobuf =
+    if (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) then
       buildPackages."protobuf_${lib.versions.major version}"
-    ];
+    else
+      (placeholder "out");
+  setupHook = ./setup-hook.sh;
+
+  nativeBuildInputs = [
+    cmake
+  ];
 
   buildInputs = [
     gtest

pkgs/development/libraries/protobuf/setup-hook.sh

@@ -0,0 +1,9 @@
+ProtobufCMakeFlags() {
+  cmakeFlagsArray+=(
+    -DPROTOC_EXE="@build_protobuf@/bin/protoc"
+    -DProtobuf_PROTOC_EXE="@build_protobuf@/bin/protoc"
+    -DProtobuf_PROTOC_EXECUTABLE="@build_protobuf@/bin/protoc"
+  )
+}
+
+preConfigureHooks+=(ProtobufCMakeFlags)