From 8e9755ab0f0825988c4955fda71bacdb2432ed28 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adri=C3=A0=20Arrufat?=
 <1671644+arrufat@users.noreply.github.com>
Date: Tue, 27 Apr 2021 20:03:32 +0900
Subject: [PATCH] do not attempt to build with gcc 4.8.5 or older (#2357)

* do not attempt to build with gcc 4.8.5 or older

* add comment
---
 dlib/CMakeLists.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/dlib/CMakeLists.txt b/dlib/CMakeLists.txt
index 8039d7156..fd266f84a 100644
--- a/dlib/CMakeLists.txt
+++ b/dlib/CMakeLists.txt
@@ -58,6 +58,12 @@ if(has_parent)
    endif()
 endif()
 
+# As of dlib 19.22, GCC 4.8.5 is no longer supported, building will fail, so let users know.
+if (CMAKE_COMPILER_IS_GNUCXX AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS_EQUAL 4.8.5)
+    message(FATAL_ERROR "${CMAKE_CXX_COMPILER} ${CMAKE_CXX_COMPILER_VERSION} is too old for dlib ${VERSION}.\n\
+    Either update your compiler to be fully compliant with C++11 or build an older version of dlib, such as 19.21.")
+endif()
+
 if (COMMAND pybind11_add_module AND MSVC)
    # True when building a python extension module using Visual Studio.  We care
    # about this because a huge number of windows users have broken systems, and