From 29ac85d55273e83a3ada19037959ae7c7823f5b7 Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Fri, 23 Apr 2021 14:17:22 +0200
Subject: CMake build: add a NLOHMANN_JSON_ORIGIN=auto/external/internal
 setting allowing to choose which nlohmann/json to use

Co-authored-by: Mike Taves <mwtoews@gmail.com>
---
 CMakeLists.txt | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

(limited to 'CMakeLists.txt')

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 66c5027f..67a8d2e1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -121,9 +121,49 @@ include(ProjConfig)
 include(ProjMac)
 include(policies)
 
+################################################################################
+# Check for nlohmann_json
+################################################################################
+
+set(NLOHMANN_JSON_ORIGIN "auto" CACHE STRING
+"nlohmann/json origin. The default auto will try to use external \
+nlohmann/json if possible")
+set_property(CACHE NLOHMANN_JSON_ORIGIN PROPERTY STRINGS auto internal external)
+
+# Probably not the strictest minimum, but known to work with it
+set(MIN_NLOHMANN_JSON_VERSION 3.7.0)
+
+if(NLOHMANN_JSON_ORIGIN STREQUAL "external")
+  find_package(nlohmann_json REQUIRED)
+  set(NLOHMANN_JSON "external")
+elseif(NLOHMANN_JSON_ORIGIN STREQUAL "internal")
+  set(NLOHMANN_JSON "internal")
+else()
+  find_package(nlohmann_json QUIET)
+  if(nlohmann_json_FOUND)
+    set(NLOHMANN_JSON "external")
+  else()
+    set(NLOHMANN_JSON "internal")
+  endif()
+endif()
+
+if(NLOHMANN_JSON STREQUAL "external")
+  # Check minimum version
+  if(nlohmann_json_VERSION VERSION_LESS MIN_NLOHMANN_JSON_VERSION)
+    message(STATUS "external nlohmann/json version ${nlohmann_json_VERSION} "
+      "is older than minimum requirement ${MIN_NLOHMANN_JSON_VERSION}")
+    set(NLOHMANN_JSON "internal")
+  else()
+    message(STATUS "found nlohmann/json version ${nlohmann_json_VERSION}")
+  endif()
+endif()
+
+message(STATUS "nlohmann/json: ${NLOHMANN_JSON}")
+
 ################################################################################
 # Check for sqlite3
 ################################################################################
+
 find_program(EXE_SQLITE3 sqlite3)
 if(NOT EXE_SQLITE3)
   message(SEND_ERROR "sqlite3 binary not found!")
-- 
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