FindcJSON: Update to play nicer with cJSON's cmake module as found in…

… vcpkg.

FindcJSON.cmake

@@ -1,11 +1,13 @@
-# Copyright 2019-2020, Collabora, Ltd.
+# Copyright 2019-2022, Collabora, Ltd.
+#
 # SPDX-License-Identifier: BSL-1.0
+#
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at
 # http://www.boost.org/LICENSE_1_0.txt)
 #
 # Original Author:
-# 2019-2020 Ryan Pavlik <[email protected]>
+# 2019-2022 Ryan Pavlik <[email protected]>
 
 #.rst:
 # FindcJSON
@@ -32,31 +34,51 @@ set(CJSON_ROOT_DIR
     "${CJSON_ROOT_DIR}"
     CACHE PATH "Root to search for cJSON")
 
-find_path(
-    CJSON_INCLUDE_DIR
-    NAMES cjson/cJSON.h
-    PATHS ${CJSON_ROOT_DIR}
-    PATH_SUFFIXES include)
-find_library(
-    CJSON_LIBRARY
-    NAMES cjson
-    PATHS ${CJSON_ROOT_DIR}
-    PATH_SUFFIXES lib)
-
 include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(cJSON REQUIRED_VARS CJSON_INCLUDE_DIR
-                                                      CJSON_LIBRARY)
+
+# Check for CMake config first.
+find_package(cJSON QUIET CONFIG)
+if(cJSON_FOUND AND TARGET cjson)
+    # Found config, let's prefer it.
+    find_package_handle_standard_args(cJSON CONFIG_MODE)
+    set(CJSON_LIBRARY cjson)
+
+else()
+    # Manually find
+    find_path(
+        CJSON_INCLUDE_DIR
+        NAMES cjson/cJSON.h
+        PATHS ${CJSON_ROOT_DIR}
+        PATH_SUFFIXES include)
+    find_library(
+        CJSON_LIBRARY
+        NAMES cjson
+        PATHS ${CJSON_ROOT_DIR}
+        PATH_SUFFIXES lib)
+
+    find_package_handle_standard_args(cJSON REQUIRED_VARS CJSON_INCLUDE_DIR
+                                                          CJSON_LIBRARY)
+endif()
+
 if(CJSON_FOUND)
     set(CJSON_INCLUDE_DIRS "${CJSON_INCLUDE_DIR}")
     set(CJSON_LIBRARIES "${CJSON_LIBRARY}")
     if(NOT TARGET cJSON::cJSON)
-        add_library(cJSON::cJSON UNKNOWN IMPORTED)
+        if(TARGET "${CJSON_LIBRARY}")
+            # Alias if we found the config file
+            add_library(cJSON::cJSON ALIAS cjson)
+        else()
+            add_library(cJSON::cJSON UNKNOWN IMPORTED)
+            set_target_properties(
+                cJSON::cJSON PROPERTIES INTERFACE_INCLUDE_DIRECTORIES
+                                        "${CJSON_INCLUDE_DIR}")
+            set_target_properties(
+                cJSON::cJSON PROPERTIES IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+                                        IMPORTED_LOCATION "${CJSON_LIBRARY}")
+
+        endif()
     endif()
-    set_target_properties(cJSON::cJSON PROPERTIES INTERFACE_INCLUDE_DIRECTORIES
-                                                  "${CJSON_INCLUDE_DIR}")
-    set_target_properties(
-        cJSON::cJSON PROPERTIES IMPORTED_LINK_INTERFACE_LANGUAGES "C"
-                                IMPORTED_LOCATION "${CJSON_LIBRARY}")
     mark_as_advanced(CJSON_INCLUDE_DIR CJSON_LIBRARY)
 endif()
+
 mark_as_advanced(CJSON_ROOT_DIR)