Eigen includes are needed in more places.

Also remove erroneous redundant extlib/eigen mentions.

CMakeLists.txt

@@ -185,9 +185,6 @@ endif()
 message(STATUS "Using in-tree libdxfrw")
 add_subdirectory(extlib/libdxfrw)
 
-message(STATUS "Using in-tree eigen")
-include_directories(extlib/eigen)
-
 message(STATUS "Using in-tree mimalloc")
 set(MI_OVERRIDE OFF CACHE BOOL "")
 set(MI_BUILD_SHARED OFF CACHE BOOL "")
@@ -199,13 +196,16 @@ set(MIMALLOC_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/extlib/mimalloc/include)
 if(NOT FORCE_VENDORED_Eigen3)
     find_package(Eigen3 CONFIG)
 endif()
-if(FORCE_VENDORED_Eigen3 OR NOT EIGEN3_FOUND)
+if(FORCE_VENDORED_Eigen3 OR NOT EIGEN3_INCLUDE_DIRS)
     message(STATUS "Using in-tree Eigen")
     set(EIGEN3_FOUND             YES)
     set(EIGEN3_INCLUDE_DIRS      ${CMAKE_SOURCE_DIR}/extlib/eigen)
 else()
     message(STATUS "Using system Eigen: ${EIGEN3_INCLUDE_DIRS}")
 endif()
+if(NOT EXISTS "${EIGEN3_INCLUDE_DIRS}")
+    message(FATAL_ERROR "Eigen 3 not found on system or in-tree")
+endif()
 
 
 if(WIN32 OR APPLE)

src/CMakeLists.txt

@@ -82,7 +82,9 @@ target_compile_definitions(slvs
     PRIVATE -DLIBRARY)
 
 target_include_directories(slvs
-    PUBLIC ${CMAKE_SOURCE_DIR}/include)
+    PUBLIC
+        ${CMAKE_SOURCE_DIR}/include
+        ${EIGEN3_INCLUDE_DIRS})
 
 target_link_libraries(slvs PRIVATE slvs_deps)
 
@@ -336,7 +338,8 @@ target_compile_definitions(solvespace-headless
     PRIVATE HEADLESS)
 
 target_include_directories(solvespace-headless
-    INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
+    INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
+    PUBLIC ${EIGEN3_INCLUDE_DIRS})
 
 target_link_libraries(solvespace-headless
     PRIVATE

test/CMakeLists.txt

@@ -76,6 +76,9 @@ target_link_libraries(solvespace-testsuite
     solvespace-headless
     ${COVERAGE_LIBRARY})
 
+target_include_directories(solvespace-testsuite
+    PRIVATE
+    ${EIGEN3_INCLUDE_DIRS})
 add_dependencies(solvespace-testsuite
     resources)