From 13c8cc58bbd829ca4616dea09cb050dc977db9ae Mon Sep 17 00:00:00 2001
From: =?utf8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Fri, 8 Apr 2022 14:57:17 +0200
Subject: [PATCH] Enable warnings when building as a developer with Clang

The configure-script logic that automatically enables warnings when
building in a development tree didn't work for Clang because it was
identified as an old GCC version.

* configure.ac: Don't test Clang version as if it were GCC.
---
 configure.ac | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/configure.ac b/configure.ac
index cda2a04be95..6b834a2f655 100644
--- a/configure.ac
+++ b/configure.ac
@@ -965,6 +965,17 @@ AC_DEFUN([gl_GCC_VERSION_IFELSE],
   ]
 )
 
+# clang is unduly picky about some things.
+AC_CACHE_CHECK([whether the compiler is clang], [emacs_cv_clang],
+  [AC_COMPILE_IFELSE(
+     [AC_LANG_PROGRAM([[
+	  #ifndef __clang__
+	    error "not clang";
+	  #endif
+        ]])],
+     [emacs_cv_clang=yes],
+     [emacs_cv_clang=no])])
+
 AC_ARG_ENABLE([gcc-warnings],
   [AS_HELP_STRING([--enable-gcc-warnings@<:@=TYPE@:>@],
                   [control generation of GCC warnings.  The TYPE 'yes'
@@ -984,7 +995,11 @@ AC_ARG_ENABLE([gcc-warnings],
    # just a release imported into Git for patch management.
    gl_gcc_warnings=no
    if test -e "$srcdir"/.git && test ! -f "$srcdir"/.tarball-version; then
-     gl_GCC_VERSION_IFELSE([5], [3], [gl_gcc_warnings=warn-only])
+      # Clang typically identifies itself as GCC 4.2 or something similar
+      # even if it is recent enough to accept the warnings we enable.
+      AS_IF([test "$emacs_cv_clang" = yes],
+         [gl_gcc_warnings=warn-only],
+         [gl_GCC_VERSION_IFELSE([5], [3], [gl_gcc_warnings=warn-only])])
    fi])
 
 AC_ARG_ENABLE([check-lisp-object-type],
@@ -996,17 +1011,6 @@ if test "$enable_check_lisp_object_type" = yes; then
     [Define to enable compile-time checks for the Lisp_Object data type.])
 fi
 
-# clang is unduly picky about some things.
-AC_CACHE_CHECK([whether the compiler is clang], [emacs_cv_clang],
-  [AC_COMPILE_IFELSE(
-     [AC_LANG_PROGRAM([[
-	  #ifndef __clang__
-	    error "not clang";
-	  #endif
-        ]])],
-     [emacs_cv_clang=yes],
-     [emacs_cv_clang=no])])
-
 WERROR_CFLAGS=
 # When compiling with GCC, prefer -isystem to -I when including system
 # include files, to avoid generating useless diagnostics for the files.
-- 
2.39.5