Use a python-script to screen and document DEVELOPER_CFLAGS

Makefile.am

@@ -23,7 +23,8 @@ EXTRA_DIST = \
 	varnishapi.pc.in \
 	varnish.m4 \
 	varnish-legacy.m4 \
-	vtc.am
+	vtc.am \
+	wflags.py
 
 AM_DISTCHECK_CONFIGURE_FLAGS = \
     --enable-developer-warnings \

configure.ac

@@ -288,11 +288,6 @@ if test "$ac_cv_have_viz" = no; then
 fi
 CFLAGS="${save_CFLAGS}"
 
-if test "x$GCC" = "xyes"; then
-	libvgz_extra_cflags="${libvgz_extra_cflags} -Wno-unknown-warning-option -Wno-implicit-fallthrough"
-	AC_SUBST(libvgz_extra_cflags)
-fi
-
 SAN_CFLAGS=
 SAN_LDFLAGS=
 UBSAN_CFLAGS=
@@ -723,31 +718,7 @@ AX_CHECK_COMPILE_FLAG([-Werror=unused-result],
       OCFLAGS="${OCFLAGS} -Wno-unused-result"])])
 
 # This corresponds to FreeBSD's WARNS level 6
-DEVELOPER_CFLAGS=" \
- -Werror \
- -Wno-format-y2k \
- -Wstrict-prototypes \
- -Wmissing-prototypes \
- -Wpointer-arith \
- -Wcast-qual \
- -Wwrite-strings \
- -Wshadow \
- -Wunused-parameter \
- -Wcast-align \
- -Wchar-subscripts \
- -Wnested-externs \
- -Wextra \
- -Wno-sign-compare \
-"
-
-# These are not compliable yet
-DEVELOPER_GCC_CFLAGS="-Wold-style-definition -Wredundant-decls "
-#DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} ${DEVELOPER_GCC_CFLAGS}"
-
-# These are compilable
-DEVELOPER_CLANG_CFLAGS="-Wmissing-variable-declarations -Wno-string-plus-int"
-# -Wno-empty-body
-#DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} ${DEVELOPER_CLANG_CFLAGS}"
+DEVELOPER_CFLAGS=`python3 wflags.py`
 
 # --enable-stack-protector
 AC_ARG_ENABLE(stack-protector,

wflags.py

+#!/usr/bin/env python3
+#
+# Copyright (c) 2021 Varnish Software AS
+# All rights reserved.
+#
+# Author: Poul-Henning Kamp <phk@phk.freebsd.dk>
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+''' Figure out what developer-warnings CC can grok '''
+
+import os
+import sys
+import subprocess
+import tempfile
+
+DESIRABLE_OPTIONS = [
+    "-fstack-protector-strong",
+    "-Werror",
+    "-Wall",
+]
+
+DESIRABLE_WFLAGS = [
+    "-Wcast-align",
+    "-Wcast-qual",
+    "-Wchar-subscripts",
+    "-Wempty-body",
+    "-Wextra",
+    "-Wformat-y2k",
+    "-Wformat-zero-length",
+    "-Wmissing-field-initializers",
+    "-Wmissing-prototypes",
+    "-Wmissing-variable-declarations",
+    "-Wnested-externs",
+    "-Wpointer-arith",
+    "-Wpointer-sign",
+    "-Wredundant-decls",
+    "-Wreturn-type",
+    "-Wshadow",
+    "-Wstrict-aliasing",
+    "-Wstrict-prototypes",
+    "-Wstring-plus-int",
+    "-Wswitch",
+    "-Wsystem-headers",
+    "-Wunused-parameter",
+    "-Wunused-parameters",
+    "-Wunused-result",
+    "-Wwrite-strings",
+]
+
+UNDESIRABLE_WFLAGS = [
+    "-Wno-thread-safety", # Does not understand our mutexs are wrapped
+    "-Wno-old-style-definition", # Does not like vgz
+    "-Wno-sign-compare", # Fixable
+    "-Wno-implicit-fallthrough", # Probably Fixable
+]
+
+def main():
+    compiler = os.environ.get("CC", "cc")
+
+    src_file = tempfile.NamedTemporaryFile(suffix='.c')
+    src_file.write(b'int main(int argc, char **argv) {(void)argc;(void)argv;return(0);}\n')
+    src_file.flush()
+    obj_file = tempfile.NamedTemporaryFile(suffix='.o')
+
+    use_flags = []
+    for i in DESIRABLE_OPTIONS + DESIRABLE_WFLAGS + UNDESIRABLE_WFLAGS:
+        j = subprocess.run(
+            [
+                compiler,
+                "-c",
+                i,
+                "-o", obj_file.name,
+                src_file.name,
+            ],
+            capture_output=True,
+        )
+        if not j.returncode and not j.stdout and not j.stderr:
+            use_flags.append(i)
+        else:
+            sys.stderr.write(compiler + " cannot " + i + '\n')
+            if b'error: unrecognized command line option' in j.stderr:
+                # LLVM
+                pass
+            elif b'warning: unknown warning option' in j.stderr:
+                # GCC
+                pass
+            else:
+                sys.stderr.write("\n\t" + j.stderr.decode('utf8') + '\n')
+    print(" ".join(use_flags))
+
+if __name__ == "__main__":
+    main()