From 96f85b151844835a1067464fc82177168c91f4ae Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Sun, 11 Aug 2024 12:02:05 +0100
Subject: [PATCH] Detect msys/gcc in configure script. Fixes #936

---
 configure.ac |  3 ++-
 m4/nvc.m4    | 30 +++++++++++++++++++++++++++---
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/configure.ac b/configure.ac
index 4ede49bd7..0d9edf8d0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -155,7 +155,7 @@ AS_IF([test "$ax_cv_prog_bison" = "yes"],
               AX_APPEND_FLAG([-Wcounterexamples], [EXTRA_YFLAGS])],
              [AC_MSG_RESULT([no])])])
 
-AX_PROG_FLEX([], [AC_MSG_ERROR(Flex not found)])
+AX_PROG_FLEX([], [AC_MSG_ERROR([Flex not found])])
 
 case $host_os in
   *cygwin*|msys*|mingw32*)
@@ -163,6 +163,7 @@ case $host_os in
     DIR_SEP=\\\\
     pathprog="cygpath -m"
     AC_CHECK_PROG([CANDLE], [candle], [yes])   # For WiX installer
+    NVC_CHECK_MSYS
     ;;
   *)
     AC_SEARCH_LIBS([dlopen], [dl dld], [], [
diff --git a/m4/nvc.m4 b/m4/nvc.m4
index 42027a81f..89bc5c2e9 100644
--- a/m4/nvc.m4
+++ b/m4/nvc.m4
@@ -2,17 +2,41 @@ dnl Check whether TLS is emulated.
 dnl Adapted from https://github.com/gcc-mirror/gcc/blob/0f1727e25f/config/tls.m4
 AC_DEFUN([NVC_CHECK_EMUTLS], [
   AC_CACHE_CHECK([whether the thread-local storage support is from emutls],
-  		 nvc_cv_use_emutls, [
+                 nvc_cv_use_emutls, [
     nvc_cv_use_emutls=no
     echo '__thread int a; int b; int main() { return a = b; }' > conftest.c
     if AC_TRY_COMMAND(${CC-cc} -Werror -S -o conftest.s conftest.c 1>&AS_MESSAGE_LOG_FD); then
       if grep __emutls_get_address conftest.s > /dev/null; then
-	nvc_cv_use_emutls=yes
+        nvc_cv_use_emutls=yes
       fi
     fi
     rm -f conftest.*
     ])
   if test "$nvc_cv_use_emutls" = "yes" ; then
     AC_DEFINE(USE_EMUTLS, 1,
-      	      [Define to 1 if the target uses emutls for thread-local storage.])
+              [Define to 1 if the target uses emutls for thread-local storage.])
   fi])
+
+dnl Ensure we are not building in the MSYS environment
+AC_DEFUN([NVC_CHECK_MSYS], [
+  AC_MSG_CHECKING([if $CC is the MSYS compiler])
+  AS_IF([$CC -dumpmachine | grep -q pc-msys],
+        [AC_MSG_RESULT([yes])
+         case "$MSYSTEM" in
+           CLANG64)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install mingw-w64-clang-x86_64-clang or pass CC=clang])
+             ;;
+           UCRT64)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install mingw-w64-ucrt-x86_64-gcc])
+             ;;
+           MINGW64)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install mingw-w64-x86_64-gcc])
+             ;;
+           MSYS)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported])
+             ;;
+           *)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install the native compiler for $MSYSTEM])
+             ;;
+         esac],
+        [AC_MSG_RESULT([no])])])