Merge pull request #182 from agoose77/feature-add-optional-target

Feature: support xtensor as an existing parent build target

Author: JohanMabille

CMakeLists.txt

@@ -44,8 +44,19 @@ message(STATUS "xtensor-blas v${${PROJECT_NAME}_VERSION}")
 # Dependencies
 # ============
 
-find_package(xtensor 0.23 REQUIRED)
-message(STATUS "Found xtensor: ${xtensor_INCLUDE_DIRS}/xtensor")
+set(xtensor_REQUIRED_VERSION 0.23.0)
+if(TARGET xtensor)
+    set(xtensor_VERSION ${XTENSOR_VERSION_MAJOR}.${XTENSOR_VERSION_MINOR}.${XTENSOR_VERSION_PATCH})
+    # Note: This is not SEMVER compatible comparison
+    if( NOT ${xtensor_VERSION} VERSION_GREATER_EQUAL ${xtensor_REQUIRED_VERSION})
+        message(ERROR "Mismatch xtensor versions. Found '${xtensor_VERSION}' but requires: '${xtensor_REQUIRED_VERSION}'")
+    else()
+        message(STATUS "Found xtensor v${xtensor_VERSION}")
+    endif()
+else()
+    find_package(xtensor ${xtensor_REQUIRED_VERSION} REQUIRED)
+    message(STATUS "Found xtensor: ${xtensor_INCLUDE_DIRS}/xtensor")
+endif()
 
 # Build
 # =====