configure: new option --enable-gcc-warnings

I have been using this change for many months in my private copy
of Emacs, and have used it to find several bugs.  It's mature
enough to publish now.
* Makefile.in (GNULIB_MODULES): Add warnings, manywarnings.
* configure.in: Support --enable-gcc-warnings, in the style of
other GNU packages such as coreutils.
(C_WARNINGS_SWITCH): Remove, replacing with...
(WARN_CFLAGS, GNULIB_WARN_CFLAGS): New variable.
(PKG_CHECK_MODULES, C_SWITCH_X_SITE): Use -isystem rather than -I,
when including system files with GCC.
* etc/NEWS: Mention --enable-gcc-warnings.
* lib/Makefile.am (AM_CFLAGS): New macro.
* m4/manywarnings.m4, m4/warnings.m4: New files, from gnulib.
* lib-src/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(BASE_CFLAGS): Use new macros rather than old.
* lwlib/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(ALL_CFLAGS): Use new macros rather than old.
* oldXMenu/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(ALL_CFLAGS): Use new macros rather than old.
* src/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(ALL_CFLAGS): Use new macros rather than old.
* src/process.c: Ignore -Wstrict-overflow to work around GCC bug 52904.
* src/regex.c: Ignore -Wstrict-overflow.  If !emacs, also ignore
-Wunused-but-set-variable, -Wunused-function, -Wunused-macros,
-Wunused-result, -Wunused-variable.  This should go away once
the Emacs and Gnulib regex code is merged.
(xmalloc, xrealloc): Now static.

2 files changed, 226 insertions, 0 deletions

diff --git a/m4/manywarnings.m4 b/m4/manywarnings.m4
new file mode 100644
index 00000000000..fd0e3722d35
--- /dev/null
+++ b/m4/manywarnings.m4
@@ -0,0 +1,184 @@
+# manywarnings.m4 serial 3
+dnl Copyright (C) 2008-2012 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl From Simon Josefsson
+
+# gl_MANYWARN_COMPLEMENT(OUTVAR, LISTVAR, REMOVEVAR)
+# --------------------------------------------------
+# Copy LISTVAR to OUTVAR except for the entries in REMOVEVAR.
+# Elements separated by whitespace.  In set logic terms, the function
+# does OUTVAR = LISTVAR \ REMOVEVAR.
+AC_DEFUN([gl_MANYWARN_COMPLEMENT],
+[
+  gl_warn_set=
+  set x $2; shift
+  for gl_warn_item
+  do
+    case " $3 " in
+      *" $gl_warn_item "*)
+        ;;
+      *)
+        gl_warn_set="$gl_warn_set $gl_warn_item"
+        ;;
+    esac
+  done
+  $1=$gl_warn_set
+])
+
+# gl_MANYWARN_ALL_GCC(VARIABLE)
+# -----------------------------
+# Add all documented GCC warning parameters to variable VARIABLE.
+# Note that you need to test them using gl_WARN_ADD if you want to
+# make sure your gcc understands it.
+AC_DEFUN([gl_MANYWARN_ALL_GCC],
+[
+  dnl First, check if -Wno-missing-field-initializers is needed.
+  dnl -Wmissing-field-initializers is implied by -W, but that issues
+  dnl warnings with GCC version before 4.7, for the common idiom
+  dnl of initializing types on the stack to zero, using { 0, }
+  AC_REQUIRE([AC_PROG_CC])
+  if test -n "$GCC"; then
+
+    dnl First, check -W -Werror -Wno-missing-field-initializers is supported
+    dnl with the current $CC $CFLAGS $CPPFLAGS.
+    AC_MSG_CHECKING([whether -Wno-missing-field-initializers is supported])
+    AC_CACHE_VAL([gl_cv_cc_nomfi_supported], [
+      gl_save_CFLAGS="$CFLAGS"
+      CFLAGS="$CFLAGS -W -Werror -Wno-missing-field-initializers"
+      AC_COMPILE_IFELSE(
+        [AC_LANG_PROGRAM([[]], [[]])],
+        [gl_cv_cc_nomfi_supported=yes],
+        [gl_cv_cc_nomfi_supported=no])
+      CFLAGS="$gl_save_CFLAGS"])
+    AC_MSG_RESULT([$gl_cv_cc_nomfi_supported])
+
+    if test "$gl_cv_cc_nomfi_supported" = yes; then
+      dnl Now check whether -Wno-missing-field-initializers is needed
+      dnl for the { 0, } construct.
+      AC_MSG_CHECKING([whether -Wno-missing-field-initializers is needed])
+      AC_CACHE_VAL([gl_cv_cc_nomfi_needed], [
+        gl_save_CFLAGS="$CFLAGS"
+        CFLAGS="$CFLAGS -W -Werror"
+        AC_COMPILE_IFELSE(
+          [AC_LANG_PROGRAM(
+             [[void f (void)
+               {
+                 typedef struct { int a; int b; } s_t;
+                 s_t s1 = { 0, };
+               }
+             ]],
+             [[]])],
+          [gl_cv_cc_nomfi_needed=no],
+          [gl_cv_cc_nomfi_needed=yes])
+        CFLAGS="$gl_save_CFLAGS"
+      ])
+      AC_MSG_RESULT([$gl_cv_cc_nomfi_needed])
+    fi
+  fi
+
+  gl_manywarn_set=
+  for gl_manywarn_item in \
+    -Wall \
+    -W \
+    -Wformat-y2k \
+    -Wformat-nonliteral \
+    -Wformat-security \
+    -Winit-self \
+    -Wmissing-include-dirs \
+    -Wswitch-default \
+    -Wswitch-enum \
+    -Wunused \
+    -Wunknown-pragmas \
+    -Wstrict-aliasing \
+    -Wstrict-overflow \
+    -Wsystem-headers \
+    -Wfloat-equal \
+    -Wtraditional \
+    -Wtraditional-conversion \
+    -Wdeclaration-after-statement \
+    -Wundef \
+    -Wshadow \
+    -Wunsafe-loop-optimizations \
+    -Wpointer-arith \
+    -Wbad-function-cast \
+    -Wc++-compat \
+    -Wcast-qual \
+    -Wcast-align \
+    -Wwrite-strings \
+    -Wconversion \
+    -Wsign-conversion \
+    -Wlogical-op \
+    -Waggregate-return \
+    -Wstrict-prototypes \
+    -Wold-style-definition \
+    -Wmissing-prototypes \
+    -Wmissing-declarations \
+    -Wmissing-noreturn \
+    -Wmissing-format-attribute \
+    -Wpacked \
+    -Wpadded \
+    -Wredundant-decls \
+    -Wnested-externs \
+    -Wunreachable-code \
+    -Winline \
+    -Winvalid-pch \
+    -Wlong-long \
+    -Wvla \
+    -Wvolatile-register-var \
+    -Wdisabled-optimization \
+    -Wstack-protector \
+    -Woverlength-strings \
+    -Wbuiltin-macro-redefined \
+    -Wmudflap \
+    -Wpacked-bitfield-compat \
+    -Wsync-nand \
+    ; do
+    gl_manywarn_set="$gl_manywarn_set $gl_manywarn_item"
+  done
+  # The following are not documented in the manual but are included in
+  # output from gcc --help=warnings.
+  for gl_manywarn_item in \
+    -Wattributes \
+    -Wcoverage-mismatch \
+    -Wmultichar \
+    -Wunused-macros \
+    ; do
+    gl_manywarn_set="$gl_manywarn_set $gl_manywarn_item"
+  done
+  # More warnings from gcc 4.6.2 --help=warnings.
+  for gl_manywarn_item in \
+    -Wabi \
+    -Wcpp \
+    -Wdeprecated \
+    -Wdeprecated-declarations \
+    -Wdiv-by-zero \
+    -Wdouble-promotion \
+    -Wendif-labels \
+    -Wextra \
+    -Wformat-contains-nul \
+    -Wformat-extra-args \
+    -Wformat-zero-length \
+    -Wformat=2 \
+    -Wmultichar \
+    -Wnormalized=nfc \
+    -Woverflow \
+    -Wpointer-to-int-cast \
+    -Wpragmas \
+    -Wsuggest-attribute=const \
+    -Wsuggest-attribute=noreturn \
+    -Wsuggest-attribute=pure \
+    -Wtrampolines \
+    ; do
+    gl_manywarn_set="$gl_manywarn_set $gl_manywarn_item"
+  done
+
+  # Disable the missing-field-initializers warning if needed
+  if test "$gl_cv_cc_nomfi_needed" = yes; then
+    gl_manywarn_set="$gl_manywarn_set -Wno-missing-field-initializers"
+  fi
+
+  $1=$gl_manywarn_set
+])
diff --git a/m4/warnings.m4 b/m4/warnings.m4
new file mode 100644
index 00000000000..c14c4801e78
--- /dev/null
+++ b/m4/warnings.m4
@@ -0,0 +1,42 @@
+# warnings.m4 serial 6
+dnl Copyright (C) 2008-2012 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl From Simon Josefsson
+
+# gl_AS_VAR_APPEND(VAR, VALUE)
+# ----------------------------
+# Provide the functionality of AS_VAR_APPEND if Autoconf does not have it.
+m4_ifdef([AS_VAR_APPEND],
+[m4_copy([AS_VAR_APPEND], [gl_AS_VAR_APPEND])],
+[m4_define([gl_AS_VAR_APPEND],
+[AS_VAR_SET([$1], [AS_VAR_GET([$1])$2])])])
+
+
+# gl_WARN_ADD(PARAMETER, [VARIABLE = WARN_CFLAGS])
+# ------------------------------------------------
+# Adds parameter to WARN_CFLAGS if the compiler supports it.  For example,
+# gl_WARN_ADD([-Wparentheses]).
+#
+# If VARIABLE is a variable name, AC_SUBST it.
+AC_DEFUN([gl_WARN_ADD],
+dnl FIXME: gl_Warn must be used unquoted until we can assume
+dnl autoconf 2.64 or newer.
+[AS_VAR_PUSHDEF([gl_Warn], [gl_cv_warn_[]_AC_LANG_ABBREV[]_$1])dnl
+AS_VAR_PUSHDEF([gl_Flags], [_AC_LANG_PREFIX[]FLAGS])dnl
+AC_CACHE_CHECK([whether _AC_LANG compiler handles $1], m4_defn([gl_Warn]), [
+  gl_save_compiler_FLAGS="$gl_Flags"
+  gl_Flags="$gl_Flags $1"
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+                    [AS_VAR_SET(gl_Warn, [yes])],
+                    [AS_VAR_SET(gl_Warn, [no])])
+  gl_Flags="$gl_save_compiler_FLAGS"
+])
+AS_VAR_IF(gl_Warn, [yes],
+  [gl_AS_VAR_APPEND(m4_if([$2], [], [[WARN_CFLAGS]], [[$2]]), [" $1"])])
+AS_VAR_POPDEF([gl_Flags])dnl
+AS_VAR_POPDEF([gl_Warn])dnl
+m4_ifval([$2], [AS_LITERAL_IF([$2], [AC_SUBST([$2])], [])])dnl
+])