From 4f68a88f5519e1bbc8b339dd48882f7f8c613edf Mon Sep 17 00:00:00 2001
From: Guillem Jover <guillem@hadrons.org>
Date: Fri, 19 Feb 2021 06:55:17 +0100
Subject: [PATCH] build: Add compiler warnings support

Detect as many warnings as possible during configure and enable them
if the user did not supply any, so that any such problem can be spotted
and fixed.
---
 .gitignore            |  1 -
 configure.ac          | 42 +++++++++++++++++++++++++++++++++++++++---
 m4/.gitignore         |  2 ++
 m4/libbsd-compiler.m4 | 24 ++++++++++++++++++++++++
 4 files changed, 65 insertions(+), 4 deletions(-)
 create mode 100644 m4/.gitignore
 create mode 100644 m4/libbsd-compiler.m4

diff --git a/.gitignore b/.gitignore
index c805925..bece823 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,5 +20,4 @@ build-aux/
 configure
 config.*
 libtool
-m4/
 stamp-h1
diff --git a/configure.ac b/configure.ac
index 09cb310..1591a93 100644
--- a/configure.ac
+++ b/configure.ac
@@ -52,9 +52,45 @@ AC_PROG_INSTALL
 AC_PROG_LN_S
 
 # Set default compiler variables
-if test "$user_CFLAGS" = unset && test "$GCC" = yes; then
-  CFLAGS="$CFLAGS -Wall -Wextra -Wno-unused-variable -Wno-unused-parameter"
-fi
+AS_IF([test "$user_CFLAGS" = unset], [
+  LIBBSD_CHECK_COMPILER_FLAG([-Wall])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wextra])
+
+  LIBBSD_CHECK_COMPILER_FLAG([-Wbad-function-cast])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wc99-c11-compat])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wcast-align])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wdeclaration-after-statement])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wdocumentation])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wduplicated-branches])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wduplicated-cond])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wformat -Wformat-security])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wformat=2])
+  LIBBSD_CHECK_COMPILER_FLAG([-Winit-self])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wlogical-not-parentheses])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wlogical-op])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wmissing-declarations])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wmissing-format-attribute])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wmissing-prototypes])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wnested-externs])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wno-missing-field-initializers])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wno-nonnull-compare])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wno-tautological-constant-out-of-range-compare])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wno-unused-parameter])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wnull-dereference])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wold-style-definition])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wpointer-arith])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wregister])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wrestrict])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wshadow])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wshift-negative-value])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wsizeof-array-argument])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wstrict-prototypes])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wswitch-bool])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wvla])
+  LIBBSD_CHECK_COMPILER_FLAG([-Wwrite-strings])
+
+  CFLAGS="$CFLAGS $LIBBSD_COMPILER_FLAGS"
+])
 
 # Checks for libraries.
 AC_CHECK_LIB([testu01], [unif01_CreateExternGenBits],
diff --git a/m4/.gitignore b/m4/.gitignore
new file mode 100644
index 0000000..10fb5d4
--- /dev/null
+++ b/m4/.gitignore
@@ -0,0 +1,2 @@
+*.m4
+!libbsd*.m4
diff --git a/m4/libbsd-compiler.m4 b/m4/libbsd-compiler.m4
new file mode 100644
index 0000000..b655b83
--- /dev/null
+++ b/m4/libbsd-compiler.m4
@@ -0,0 +1,24 @@
+# Copyright © 2021 Guillem Jover <guillem@hadrons.org>
+
+# LIBBSD_CHECK_COMPILER_FLAG
+# -------------------------
+AC_DEFUN([LIBBSD_CHECK_COMPILER_FLAG], [
+  AS_VAR_PUSHDEF([libbsd_varname_cache], [libbsd_cv_cflags_$1])
+  AC_CACHE_CHECK([whether $CC accepts $1], [libbsd_varname_cache], [
+    m4_define([libbsd_check_flag], m4_bpatsubst([$1], [^-Wno-], [-W]))
+    AS_VAR_COPY([libbsd_save_CFLAGS], [CFLAGS])
+    AS_VAR_SET([CFLAGS], ["-Werror libbsd_check_flag"])
+    AC_COMPILE_IFELSE([
+      AC_LANG_SOURCE([[]])
+    ], [
+      AS_VAR_SET([libbsd_varname_cache], [yes])
+    ], [
+      AS_VAR_SET([libbsd_varname_cache], [no])
+    ])
+    AS_VAR_COPY([CFLAGS], [libbsd_save_CFLAGS])
+  ])
+  AS_VAR_IF([libbsd_varname_cache], [yes], [
+    AS_VAR_APPEND([LIBBSD_COMPILER_FLAGS], [" $1"])
+  ])
+  AS_VAR_POPDEF([libbsd_varname_cache])
+])
-- 
2.47.3