Improve eigen.cmake laplacke support

Author: zfergus

cmake/recipes/eigen.cmake

@@ -45,14 +45,26 @@ if(EIGEN_WITH_MKL)
         EIGEN_USE_LAPACKE_STRICT
     )
 elseif(APPLE)
-    target_link_libraries(Eigen3_Eigen INTERFACE
-        "-framework Accelerate"
-        "/opt/homebrew/opt/lapack/lib/liblapacke.dylib"
-    )
-    target_compile_definitions(Eigen3_Eigen INTERFACE
-        EIGEN_USE_BLAS
-        EIGEN_USE_LAPACKE_STRICT
+    find_package(BLAS REQUIRED)
+    find_library(LAPACKE lapacke PATHS
+        "/opt/local/lib/lapack"
+        "/opt/homebrew/opt/lapack/lib"
     )
+    if (NOT LAPACKE)
+        # BLAS should be available on macOS, but LAPACKE might not be
+        message(WARNING "LAPACKE library not found (required for EIGEN_USE_LAPACKE on macOS)! "
+            "Perhaps you need to install it (e.g., brew install lapack). "
+            "Eigen will be built without LAPACKE support.")
+    else()
+        message(STATUS "Found BLAS and LAPACKE. Enabling Eigen LAPACKE support.")
+        target_link_libraries(Eigen3_Eigen INTERFACE
+            ${BLAS_LIBRARIES} ${LAPACKE}
+        )
+        target_compile_definitions(Eigen3_Eigen INTERFACE
+            EIGEN_USE_BLAS
+            EIGEN_USE_LAPACKE_STRICT
+        )
+    endif()
 endif()
 
 # On Windows, enable natvis files to improve debugging experience