From f049836d686f5e7817682e700c3f4822fa03c9e7 Mon Sep 17 00:00:00 2001
From: Axel Huebl <axel.huebl@plasma.ninja>
Date: Fri, 2 Nov 2018 10:15:27 +0100
Subject: [PATCH] CMake: Optional Install if Embedded

When adding this library as embedded library with private
"target link", e.g. only used inside private source files, the
library does not need to be installed when the main project gets
installed.

This adds an additional option `JSON_Install` similar to the
test-build control switch in order to skip installing headers and
CMake config files if requested.

Avoids using
```cmake
add_subdirectory(path/to/nlohmann_json EXCLUDE_FROM_ALL)
```

which has further side-effects:
https://cmake.org/cmake/help/v3.0/command/add_subdirectory.html
---
 CMakeLists.txt | 57 ++++++++++++++++++++++++++------------------------
 README.md      |  4 ++++
 2 files changed, 34 insertions(+), 27 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 230cbff88a..716abf9d44 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,6 +16,7 @@ include(ExternalProject)
 ## OPTIONS
 ##
 option(JSON_BuildTests "Build the unit tests when BUILD_TESTING is enabled." ON)
+option(JSON_Install "Install CMake targets during install step." ON)
 option(JSON_MultipleHeaders "Use non-amalgamated version of the library." OFF)
 
 ##
@@ -92,32 +93,34 @@ configure_file(
     @ONLY
 )
 
-install(
-    DIRECTORY ${NLOHMANN_JSON_INCLUDE_BUILD_DIR}
-    DESTINATION ${NLOHMANN_JSON_INCLUDE_INSTALL_DIR}
-)
-install(
-    FILES ${NLOHMANN_JSON_CMAKE_PROJECT_CONFIG_FILE} ${NLOHMANN_JSON_CMAKE_VERSION_CONFIG_FILE}
-    DESTINATION ${NLOHMANN_JSON_CONFIG_INSTALL_DIR}
-)
-if (NLOHMANN_ADD_NATVIS)
+if(JSON_Install)
     install(
-        FILES ${NLOHMANN_NATVIS_FILE}
-        DESTINATION .
-)
+        DIRECTORY ${NLOHMANN_JSON_INCLUDE_BUILD_DIR}
+        DESTINATION ${NLOHMANN_JSON_INCLUDE_INSTALL_DIR}
+    )
+    install(
+        FILES ${NLOHMANN_JSON_CMAKE_PROJECT_CONFIG_FILE} ${NLOHMANN_JSON_CMAKE_VERSION_CONFIG_FILE}
+        DESTINATION ${NLOHMANN_JSON_CONFIG_INSTALL_DIR}
+    )
+    if (NLOHMANN_ADD_NATVIS)
+        install(
+            FILES ${NLOHMANN_NATVIS_FILE}
+            DESTINATION .
+    )
+    endif()
+    export(
+        TARGETS ${NLOHMANN_JSON_TARGET_NAME}
+        NAMESPACE ${PROJECT_NAME}::
+        FILE ${NLOHMANN_JSON_CMAKE_PROJECT_TARGETS_FILE}
+    )
+    install(
+        TARGETS ${NLOHMANN_JSON_TARGET_NAME}
+        EXPORT ${NLOHMANN_JSON_TARGETS_EXPORT_NAME}
+        INCLUDES DESTINATION ${NLOHMANN_JSON_INCLUDE_INSTALL_DIR}
+    )
+    install(
+        EXPORT ${NLOHMANN_JSON_TARGETS_EXPORT_NAME}
+        NAMESPACE ${PROJECT_NAME}::
+        DESTINATION ${NLOHMANN_JSON_CONFIG_INSTALL_DIR}
+    )
 endif()
-export(
-    TARGETS ${NLOHMANN_JSON_TARGET_NAME}
-    NAMESPACE ${PROJECT_NAME}::
-    FILE ${NLOHMANN_JSON_CMAKE_PROJECT_TARGETS_FILE}
-)
-install(
-    TARGETS ${NLOHMANN_JSON_TARGET_NAME}
-    EXPORT ${NLOHMANN_JSON_TARGETS_EXPORT_NAME}
-    INCLUDES DESTINATION ${NLOHMANN_JSON_INCLUDE_INSTALL_DIR}
-)
-install(
-    EXPORT ${NLOHMANN_JSON_TARGETS_EXPORT_NAME}
-    NAMESPACE ${PROJECT_NAME}::
-    DESTINATION ${NLOHMANN_JSON_CONFIG_INSTALL_DIR}
-)
diff --git a/README.md b/README.md
index 1154a62eaf..818a12697b 100644
--- a/README.md
+++ b/README.md
@@ -97,6 +97,10 @@ To embed the library directly into an existing CMake project, place the entire s
 # run from your own project's code.
 set(JSON_BuildTests OFF CACHE INTERNAL "")
 
+# If you only include this third party in PRIVATE source files, you do not
+# need to install it when your main project gets installed.
+# set(JSON_Install OFF CACHE INTERNAL "")
+
 # Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it
 # inintended consequences that will break the build.  It's generally
 # discouraged (although not necessarily well documented as such) to use