From c18ed7236db5720bab383e6de78415177922bff3 Mon Sep 17 00:00:00 2001
From: Vitaly Lipatov <lav@etersoft.ru>
Date: Thu, 30 Jan 2020 13:55:42 +0300
Subject: GNUInstallDirs: Warn when CMAKE_SYSTEM_NAME is not set

If a project writes `include(GNUInstallDirs)` before `project()` then
`CMAKE_SYSTEM_NAME` may not be set and an incorrect `LIBDIR` may be
computed.  Warn about this case.
---
 Modules/GNUInstallDirs.cmake                      | 19 +++++++++----------
 Tests/RunCMake/GNUInstallDirs/NoSystem-stderr.txt |  8 ++++++++
 Tests/RunCMake/GNUInstallDirs/NoSystem.cmake      |  2 ++
 Tests/RunCMake/GNUInstallDirs/RunCMakeTest.cmake  |  3 +++
 4 files changed, 22 insertions(+), 10 deletions(-)
 create mode 100644 Tests/RunCMake/GNUInstallDirs/NoSystem-stderr.txt
 create mode 100644 Tests/RunCMake/GNUInstallDirs/NoSystem.cmake

diff --git a/Modules/GNUInstallDirs.cmake b/Modules/GNUInstallDirs.cmake
index f95e6e2..9ef22b9 100644
--- a/Modules/GNUInstallDirs.cmake
+++ b/Modules/GNUInstallDirs.cmake
@@ -221,6 +221,11 @@ if(NOT DEFINED CMAKE_INSTALL_LIBDIR OR (_libdir_set
     # default one. When CMAKE_INSTALL_PREFIX changes, the value is
     # updated to the new default, unless the user explicitly changed it.
   endif()
+  if (NOT DEFINED CMAKE_SYSTEM_NAME OR NOT DEFINED CMAKE_SIZEOF_VOID_P)
+    message(AUTHOR_WARNING
+      "Unable to determine default CMAKE_INSTALL_LIBDIR directory because no target architecture is known. "
+      "Please enable at least one language before including GNUInstallDirs.")
+  endif()
   if(CMAKE_SYSTEM_NAME MATCHES "^(Linux|kFreeBSD|GNU)$"
       AND NOT CMAKE_CROSSCOMPILING
       AND NOT EXISTS "/etc/arch-release")
@@ -235,16 +240,10 @@ if(NOT DEFINED CMAKE_INSTALL_LIBDIR OR (_libdir_set
         endif()
       endif()
     else() # not debian, rely on CMAKE_SIZEOF_VOID_P:
-      if(NOT DEFINED CMAKE_SIZEOF_VOID_P)
-        message(AUTHOR_WARNING
-          "Unable to determine default CMAKE_INSTALL_LIBDIR directory because no target architecture is known. "
-          "Please enable at least one language before including GNUInstallDirs.")
-      else()
-        if("${CMAKE_SIZEOF_VOID_P}" EQUAL "8")
-          set(_LIBDIR_DEFAULT "lib64")
-          if(DEFINED _GNUInstallDirs_LAST_CMAKE_INSTALL_PREFIX)
-            set(__LAST_LIBDIR_DEFAULT "lib64")
-          endif()
+      if("${CMAKE_SIZEOF_VOID_P}" EQUAL "8")
+        set(_LIBDIR_DEFAULT "lib64")
+        if(DEFINED _GNUInstallDirs_LAST_CMAKE_INSTALL_PREFIX)
+          set(__LAST_LIBDIR_DEFAULT "lib64")
         endif()
       endif()
     endif()
diff --git a/Tests/RunCMake/GNUInstallDirs/NoSystem-stderr.txt b/Tests/RunCMake/GNUInstallDirs/NoSystem-stderr.txt
new file mode 100644
index 0000000..36f064c
--- /dev/null
+++ b/Tests/RunCMake/GNUInstallDirs/NoSystem-stderr.txt
@@ -0,0 +1,8 @@
+^CMake Warning \(dev\) at .*/Modules/GNUInstallDirs.cmake:[0-9]+ \(message\):
+  Unable to determine default CMAKE_INSTALL_LIBDIR directory because no
+  target architecture is known.  Please enable at least one language before
+  including GNUInstallDirs.
+Call Stack \(most recent call first\):
+  NoSystem.cmake:[0-9]+ \(include\)
+  CMakeLists.txt:[0-9]+ \(include\)
+This warning is for project developers.  Use -Wno-dev to suppress it.$
diff --git a/Tests/RunCMake/GNUInstallDirs/NoSystem.cmake b/Tests/RunCMake/GNUInstallDirs/NoSystem.cmake
new file mode 100644
index 0000000..19cf7be
--- /dev/null
+++ b/Tests/RunCMake/GNUInstallDirs/NoSystem.cmake
@@ -0,0 +1,2 @@
+unset(CMAKE_SYSTEM_NAME)
+include(GNUInstallDirs)
diff --git a/Tests/RunCMake/GNUInstallDirs/RunCMakeTest.cmake b/Tests/RunCMake/GNUInstallDirs/RunCMakeTest.cmake
index d671ee0..eb2c1a2 100644
--- a/Tests/RunCMake/GNUInstallDirs/RunCMakeTest.cmake
+++ b/Tests/RunCMake/GNUInstallDirs/RunCMakeTest.cmake
@@ -16,4 +16,7 @@ foreach(case
     )
   set(RunCMake-stderr-file ${case}${variant}-stderr.txt)
   run_cmake(${case})
+  unset(RunCMake-stderr-file)
 endforeach()
+
+run_cmake(NoSystem)
-- 
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