opencv: fix build & cmake

[choyy]

cmake error: #8484

CMake Error at /github/home/.xmake/packages/o/opencv/4.12.0/f64cc25c8ea945fd9fed9b60af1ed663/lib/cmake/opencv4/OpenCVModules.cmake:363 (set_target_properties):
  The link interface of target "opencv_wechat_qrcode" contains:

    Iconv::Iconv

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.

Call Stack (most recent call first):
  /github/home/.xmake/packages/o/opencv/4.12.0/f64cc25c8ea945fd9fed9b60af1ed663/lib/cmake/opencv4/OpenCVConfig.cmake:128 (include)
  CMakeLists.txt:221 (FIND_PACKAGE)

[gemini-code-assist]

Summary of Changes

Hello @choyy, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request aims to resolve build and CMake-related issues encountered with OpenCV, particularly for version 4.12.0. It introduces a new patch for this specific version and modifies the CMake configuration to ensure proper dependency resolution, specifically for the Iconv library when building modules like opencv_wechat_qrcode. These changes are intended to fix a reported CMake error and improve the overall build stability for OpenCV.

Highlights

• OpenCV 4.12.0 Patch: A new patch has been added specifically for OpenCV version 4.12.0, likely addressing specific issues or improvements for this version.
• CMake Dependency Fix: The build configuration has been updated to correctly handle CMake dependencies. This includes adding include(CMakeFindDependencyMacro) and find_dependency(Iconv) to OpenCVModules.cmake for the opencv_wechat_qrcode module, resolving a reported CMake error.

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[gemini-code-assist]

Code Review

The pull request addresses a CMake build error by adding a new patch for OpenCV 4.12.0 and correcting a typo in the cmake.install function. Additionally, it modifies the generated OpenCVModules.cmake to include find_dependency(Iconv), which implies a new dependency on libiconv for projects consuming OpenCV. While the typo fix is a good improvement, the implicit dependency on libiconv should be explicitly declared in the opencv package's xmake.lua to ensure proper dependency management.

[gemini-code-assist]

The addition of find_dependency(Iconv) in OpenCVModules.cmake indicates that libiconv is now a dependency for OpenCV, specifically for modules like opencv_wechat_qrcode. However, libiconv is not explicitly added as a dependency in the opencv package's on_load function. This can lead to build failures for downstream projects if libiconv is not available or properly managed by xmake. Please add package:add("deps", "libiconv") to ensure this dependency is correctly handled.

[luadebug]

opencv/opencv#20404 (comment)
Maybe related, as for MinGW.

If zxing.hpp is like this (according to contrib resource https://codeload.github.com/opencv/opencv_contrib/tar.gz/refs/tags/4.12.0): That would be if not package:is_plat("windows", "android") ?

#if defined(__ANDROID_API__) || defined(_MSC_VER)

#ifndef NO_ICONV
#define NO_ICONV
#endif

#endif

If we apply lebarsfa/Packages@4b271d2#diff-e13272f82adfb96ae33f958418128ddbc9bd47bc4819f0ddb82ca6358f365bc6 choco/libopencv-dev/tools/no_iconv_mingw.patch that would be if not package:is_plat("windows", "android", "mingw") ?

[choyy]

opencv/opencv_contrib#2916 disabled MinGW, opencv/opencv_contrib#2931 enabled MinGW later. Then it would be not package:is_plat("windows", "android"). But I'm not sure if the cmake file is like lib/cmake/opencv4/OpenCVModules.cmake on MinGW.

[luadebug]

Everything looks good, if we could do check by package version for MinGW filter maybe it would be better...?

[choyy]

It seems no version was released during MinGW was disabled?