From 0f68d133fa6fd2973951b8aaab481e34bbfd2cf4 Mon Sep 17 00:00:00 2001
From: hannesweisbach <hannesweisbach@users.noreply.github.com>
Date: Thu, 29 Nov 2018 00:37:59 +0100
Subject: Suppress Warnings in GSL Headers (#731)

Suppress warnings in GSL headers using the SYSTEM keyword for target_include_directories(). This enables developers to see warnings standalone builds but hides them from users in non-standalone builds.
---
 CMakeLists.txt | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b0de85d..71011b1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -51,11 +51,21 @@ target_compile_definitions(GSL INTERFACE
 )
 
 # add include folders to the library and targets that consume it
-target_include_directories(GSL INTERFACE
-    $<BUILD_INTERFACE:
-        ${CMAKE_CURRENT_SOURCE_DIR}/include
-    >
-)
+# the SYSTEM keyword suppresses warnings for users of the library
+if(GSL_STANDALONE_PROJECT)
+    target_include_directories(GSL INTERFACE
+        $<BUILD_INTERFACE:
+            ${CMAKE_CURRENT_SOURCE_DIR}/include
+        >
+    )
+else()
+    target_include_directories(GSL SYSTEM INTERFACE
+        $<BUILD_INTERFACE:
+            ${CMAKE_CURRENT_SOURCE_DIR}/include
+        >
+    )
+endif()
+
 
 if ((CMAKE_VERSION GREATER 3.7.9) OR (CMAKE_VERSION EQUAL 3.7.9))
     if (MSVC_IDE)
-- 
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