From e2f25d3e8218fe0ae02680966b71cba8755d38de Mon Sep 17 00:00:00 2001
From: Daniel Pfeifer <daniel@pfeifer-mail.de>
Date: Mon, 6 Mar 2017 20:52:09 +0100
Subject: WriteCompilerDetectionHeader: fix STATIC_ASSERT

fixes #16185
---
 Modules/WriteCompilerDetectionHeader.cmake              | 17 +++++++++++++----
 Tests/Module/WriteCompilerDetectionHeader/main.cpp      |  3 +++
 .../Module/WriteCompilerDetectionHeader/multi_files.cpp |  3 +++
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Modules/WriteCompilerDetectionHeader.cmake b/Modules/WriteCompilerDetectionHeader.cmake
index 0b16aa4..362099e 100644
--- a/Modules/WriteCompilerDetectionHeader.cmake
+++ b/Modules/WriteCompilerDetectionHeader.cmake
@@ -503,10 +503,19 @@ function(write_compiler_detection_header
       if (feature STREQUAL cxx_static_assert)
         set(def_value "${prefix_arg}_STATIC_ASSERT(X)")
         set(def_value_msg "${prefix_arg}_STATIC_ASSERT_MSG(X, MSG)")
-        set(static_assert_struct "template<bool> struct ${prefix_arg}StaticAssert;\ntemplate<> struct ${prefix_arg}StaticAssert<true>{};\n")
-        set(def_standard "#    define ${def_value} static_assert(X, #X)\n#    define ${def_value_msg} static_assert(X, MSG)")
-        set(def_alternative "${static_assert_struct}#    define ${def_value} sizeof(${prefix_arg}StaticAssert<X>)\n#    define ${def_value_msg} sizeof(${prefix_arg}StaticAssert<X>)")
-        string(APPEND file_content "#  if defined(${def_name}) && ${def_name}\n${def_standard}\n#  else\n${def_alternative}\n#  endif\n\n")
+        set(def_fallback "enum { ${prefix_arg}_STATIC_ASSERT_JOIN(${prefix_arg}StaticAssertEnum, __LINE__) = sizeof(${prefix_arg}StaticAssert<X>) }")
+        string(APPEND file_content "#  if defined(${def_name}) && ${def_name}
+#    define ${def_value} static_assert(X, #X)
+#    define ${def_value_msg} static_assert(X, MSG)
+#  else
+#    define ${prefix_arg}_STATIC_ASSERT_JOIN(X, Y) ${prefix_arg}_STATIC_ASSERT_JOIN_IMPL(X, Y)
+#    define ${prefix_arg}_STATIC_ASSERT_JOIN_IMPL(X, Y) X##Y
+template<bool> struct ${prefix_arg}StaticAssert;
+template<> struct ${prefix_arg}StaticAssert<true>{};
+#    define ${def_value} ${def_fallback}
+#    define ${def_value_msg} ${def_fallback}
+#  endif
+\n")
       endif()
       if (feature STREQUAL cxx_alignas)
         set(def_value "${prefix_arg}_ALIGNAS(X)")
diff --git a/Tests/Module/WriteCompilerDetectionHeader/main.cpp b/Tests/Module/WriteCompilerDetectionHeader/main.cpp
index 192094c..9979cba 100644
--- a/Tests/Module/WriteCompilerDetectionHeader/main.cpp
+++ b/Tests/Module/WriteCompilerDetectionHeader/main.cpp
@@ -8,6 +8,9 @@
 #error Expect no C features defined
 #endif
 
+TEST_STATIC_ASSERT(true);
+TEST_STATIC_ASSERT_MSG(true, "msg");
+
 int main()
 {
   return 0;
diff --git a/Tests/Module/WriteCompilerDetectionHeader/multi_files.cpp b/Tests/Module/WriteCompilerDetectionHeader/multi_files.cpp
index 1635091..d1f178f 100644
--- a/Tests/Module/WriteCompilerDetectionHeader/multi_files.cpp
+++ b/Tests/Module/WriteCompilerDetectionHeader/multi_files.cpp
@@ -8,6 +8,9 @@
 #error Expect no C features defined
 #endif
 
+MULTI_STATIC_ASSERT(true);
+MULTI_STATIC_ASSERT_MSG(true, "msg");
+
 int main()
 {
   return 0;
-- 
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