File flann_prefer_cmake_config.patch of Package openMVG

From a462f9f7fd643399f414a236fc14be4eb46fd637 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Br=C3=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Thu, 19 Jan 2023 04:34:30 +0100
Subject: [PATCH] Prefer CMake Config when looking for Flann

Latest flann may link to e.g. liblz4, and the FindFlann module does not
handle transitive lib dependencies.

In case external flann is required try the upstream CMake Config first,
and fall back to the legacy lookup.

Fixes #1265.
---
 src/CMakeLists.txt | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index bb9b2eca5..af920fc68 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -322,8 +322,15 @@ endif()
 if (NOT DEFINED FLANN_INCLUDE_DIR_HINTS)
   set(FLANN_INCLUDE_DIR_HINTS ${CMAKE_CURRENT_SOURCE_DIR}/third_party/flann/src/cpp)
   set(OpenMVG_USE_INTERNAL_FLANN ON)
+  find_package(Flann QUIET)
+else()
+  find_package(Flann QUIET CONFIG)
+  if (TARGET flann::flann)
+    set(FLANN_LIBRARIES "flann::flann;flann::flann_cpp")
+  else()
+    find_package(Flann QUIET)
+  endif()
 endif()
-find_package(Flann QUIET)
 if (NOT FLANN_FOUND OR OpenMVG_USE_INTERNAL_FLANN)
   set(FLANN_INCLUDE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/third_party/flann/src/cpp)
 endif()