opencv: fix cross compliation by patching protobuf

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

@@ -3,6 +3,7 @@
   stdenv,
   fetchurl,
   fetchFromGitHub,
+  fetchpatch2,
   cmake,
   pkg-config,
   unzip,
@@ -300,6 +301,13 @@ effectiveStdenv.mkDerivation {
   patches =
     [
       ./cmake-don-t-use-OpenCVFindOpenEXR.patch
+      # NOTE: remove patch in opencv v4.12.0 (next release)
+      # https://github.com/opencv/opencv/pull/27428
+      # it is required to allow cross compilation by letting PROTOC_EXE be set by protobuf hook
+      (fetchpatch2 {
+        url = "https://github.com/opencv/opencv/commit/bbe2f50b5d50a282b2260100be9e559067e55fbf.patch?full_index=1";
+        hash = "sha256-T+zmrOeyEmNyu1hJPDGUub59EMXwe6ZqP6PV/tDJFCk=";
+      })
     ]
     ++ optionals enableCuda [
       ./cuda_opt_flow.patch

pkgs/development/libraries/protobuf/cmake-configure-protoc-exe-21.patch

@@ -0,0 +1,47 @@
+commit 649864521c0e09f3a3bd7939d91ba1ef488946dc
+Author: phanirithvij <phanirithvij2000@gmail.com>
+Date:   Tue Jun 10 10:58:49 2025 +0530
+
+    [CMake] Allow for protoc executable to be configured
+
+    copied from commit 3163111b6fb1da08b9d6ad75518d91b89cd03bbf
+
+    Signed-off-by: phanirithvij <phanirithvij2000@gmail.com>
+
+diff --git a/cmake/protobuf-config.cmake.in b/cmake/protobuf-config.cmake.in
+index 61669118c..55f32516f 100644
+--- a/cmake/protobuf-config.cmake.in
++++ b/cmake/protobuf-config.cmake.in
+@@ -11,7 +11,7 @@ function(protobuf_generate)
+   include(CMakeParseArguments)
+
+   set(_options APPEND_PATH)
+-  set(_singleargs LANGUAGE OUT_VAR EXPORT_MACRO PROTOC_OUT_DIR PLUGIN PLUGIN_OPTIONS)
++  set(_singleargs LANGUAGE OUT_VAR EXPORT_MACRO PROTOC_OUT_DIR PLUGIN PLUGIN_OPTIONS PROTOC_EXE)
+   if(COMMAND target_sources)
+     list(APPEND _singleargs TARGET)
+   endif()
+@@ -92,6 +92,11 @@ function(protobuf_generate)
+     endforeach()
+   endif()
+
++  if(NOT protobuf_generate_PROTOC_EXE)
++    # Default to using the CMake executable
++    set(protobuf_generate_PROTOC_EXE protobuf::protoc)
++  endif()
++
+   foreach(DIR ${protobuf_generate_IMPORT_DIRS})
+     get_filename_component(ABS_PATH ${DIR} ABSOLUTE)
+     list(FIND _protobuf_include_path ${ABS_PATH} _contains_already)
+@@ -146,9 +151,9 @@ function(protobuf_generate)
+
+     add_custom_command(
+       OUTPUT ${_generated_srcs}
+-      COMMAND protobuf::protoc
++      COMMAND ${protobuf_generate_PROTOC_EXE}
+       ARGS ${protobuf_generate_PROTOC_OPTIONS} --${protobuf_generate_LANGUAGE}_out ${_plugin_options}:${protobuf_generate_PROTOC_OUT_DIR} ${_plugin} ${_protobuf_include_path} ${_abs_file}
+-      DEPENDS ${_abs_file} protobuf::protoc
++      DEPENDS ${_abs_file} ${protobuf_generate_PROTOC_EXE}
+       COMMENT ${_comment}
+       VERBATIM )
+   endforeach()

pkgs/development/libraries/protobuf/generic.nix

@@ -13,7 +13,6 @@
   zlib,
   version,
   hash,
-  replaceVars,
   versionCheckHook,
 
   # downstream dependencies
@@ -42,14 +41,27 @@ stdenv.mkDerivation (finalAttrs: {
       --replace-fail 'tmpnam(b)' '"'$TMPDIR'/foo"'
   '';
 
-  patches = lib.optionals (lib.versionOlder version "22") [
-    # fix protobuf-targets.cmake installation paths, and allow for CMAKE_INSTALL_LIBDIR to be absolute
-    # https://github.com/protocolbuffers/protobuf/pull/10090
-    (fetchpatch {
-      url = "https://github.com/protocolbuffers/protobuf/commit/a7324f88e92bc16b57f3683403b6c993bf68070b.patch";
-      hash = "sha256-SmwaUjOjjZulg/wgNmR/F5b8rhYA2wkKAjHIOxjcQdQ=";
-    })
-  ];
+  patches =
+    lib.optionals (lib.versionOlder version "22") [
+      # fix protobuf-targets.cmake installation paths, and allow for CMAKE_INSTALL_LIBDIR to be absolute
+      # https://github.com/protocolbuffers/protobuf/pull/10090
+      (fetchpatch {
+        url = "https://github.com/protocolbuffers/protobuf/commit/a7324f88e92bc16b57f3683403b6c993bf68070b.patch";
+        hash = "sha256-SmwaUjOjjZulg/wgNmR/F5b8rhYA2wkKAjHIOxjcQdQ=";
+      })
+    ]
+    ++ lib.optionals (lib.head (lib.splitVersion version) == "21") [
+      # patch 3163111b6fb1da08b9d6ad75518d91b89cd03bbf with additional modifications
+      ./cmake-configure-protoc-exe-21.patch
+    ]
+    ++ lib.optionals (lib.versionAtLeast version "22" && lib.versionOlder version "29") [
+      # for cross compilation allow for invocations of `protobuf_generate` pass their preferred programs
+      # https://github.com/protocolbuffers/protobuf/pull/17888 (in tree from 29 onwards)
+      (fetchpatch {
+        url = "https://github.com/protocolbuffers/protobuf/commit/3163111b6fb1da08b9d6ad75518d91b89cd03bbf.patch";
+        hash = "sha256-px085y1MRt9qgYHCqR7ZOaNaHO1RV+VK3WWaI9I9wPg=";
+      })
+    ];
 
   # hook to provide the path to protoc executable, used at build time
   build_protobuf =