build: better check for compiler flags; we no longer try to use

flags that autoconf hasn’t checked first.

build/autotools/m4/lol-misc.m4

@@ -0,0 +1,32 @@
+
+dnl LOL_TRY_CFLAGS (CFLAGS, [ACTION-IF-WORKS], [ACTION-IF-FAILS])
+dnl check if $CC supports a given set of cflags
+AC_DEFUN([LOL_TRY_CFLAGS],
+    [AC_MSG_CHECKING([if $CC supports $1 flags])
+    save_CFLAGS="$CFLAGS"
+    CFLAGS="$1"
+    AC_TRY_COMPILE([],[],[ac_cv_try_cflags_ok=yes],[ac_cv_try_cflags_ok=no])
+    CFLAGS="$save_CFLAGS"
+    AC_MSG_RESULT([$ac_cv_try_cflags_ok])
+    if test x"$ac_cv_try_cflags_ok" = x"yes"; then
+        ifelse([$2],[],[:],[$2])
+    else
+        ifelse([$3],[],[:],[$3])
+    fi])
+
+dnl LOL_TRY_CXXFLAGS (CXXFLAGS, [ACTION-IF-WORKS], [ACTION-IF-FAILS])
+dnl check if $CXX supports a given set of cxxflags
+AC_DEFUN([LOL_TRY_CXXFLAGS],
+    [AC_MSG_CHECKING([if $CXX supports $1 flags])
+    AC_LANG_PUSH(C++)
+    save_CXXFLAGS="$CXXFLAGS"
+    CXXFLAGS="$1"
+    AC_TRY_COMPILE([],[],[ac_cv_try_cxxflags_ok=yes],[ac_cv_try_cxxflags_ok=no])
+    CXXFLAGS="$save_CXXFLAGS"
+    AC_MSG_RESULT([$ac_cv_try_cxxflags_ok])
+    if test x"$ac_cv_try_cxxflags_ok" = x"yes"; then
+        ifelse([$2],[],[:],[$2])
+    else
+        ifelse([$3],[],[:],[$3])
+    fi
+    AC_LANG_POP(C++)])

configure.ac

@@ -139,12 +139,28 @@ AM_CONDITIONAL(BUILD_DOCUMENTATION, test "${DOXYGEN}" != "no")
 AM_CONDITIONAL(USE_LATEX, test "${LATEX}" != "no")
 AM_CONDITIONAL(USE_DOT, test "${DOT}" != "no")
 
-dnl No exceptions
-AM_CXXFLAGS="${AM_CXXFLAGS} -fno-exceptions -fno-rtti"
-dnl Optimizations
+
+dnl  No exceptions
+LOL_TRY_CXXFLAGS(-fno-exceptions, [AM_CXXFLAGS="${AM_CXXFLAGS} -fno-exceptions"])
+LOL_TRY_CXXFLAGS(-fno-rtti, [AM_CXXFLAGS="${AM_CXXFLAGS} -fno-rtti"])
+
+dnl  Optimizations
 AM_CXXFLAGS="${AM_CXXFLAGS} ${REL} ${OPT}"
-dnl Code qui fait des warnings == code de porc == deux baffes dans ta gueule
-AM_CPPFLAGS="${AM_CPPFLAGS} -Wall -Wextra -Wpointer-arith -Wcast-align -Wcast-qual -Wshadow -Wsign-compare"
+
+dnl  Code qui fait des warnings == code de porc == deux baffes dans ta gueule
+LOL_TRY_CXXFLAGS(-Wall, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wall"])
+LOL_TRY_CXXFLAGS(-Wextra, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wextra"])
+LOL_TRY_CXXFLAGS(-Wpointer-arith, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wpointer-arith"])
+LOL_TRY_CXXFLAGS(-Wcast-align, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wcast-align"])
+LOL_TRY_CXXFLAGS(-Wcast-qual, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wcast-qual"])
+LOL_TRY_CXXFLAGS(-Wshadow, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wshadow"])
+LOL_TRY_CXXFLAGS(-Wsign-compare, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wsign-compare"])
+
+dnl  Add these even though they're implicitly set, so that we can safely
+dnl  remove them from within a Makefile.
+LOL_TRY_CXXFLAGS(-Wno-maybe-uninitialized, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wno-maybe-uninitialized"])
+LOL_TRY_CXXFLAGS(-Wno-narrowing, [AM_CPPFLAGS="${AM_CPPFLAGS} -Wno-narrowing"])
+
 
 AC_CHECK_LIB(m, sin, MATH_LIBS="${MATH_LIBS} -lm")
 AC_CHECK_LIB(pthread, main, LIBS="$LIBS -lpthread")

src/bullet/Makefile.am

@@ -3,10 +3,15 @@ include $(top_srcdir)/build/autotools/common.am
 
 noinst_LIBRARIES = liblolbullet.a
 
+# Only remove flags that were actually set, because we don't know
+# what the compiler actually accepts.
+disable_cflags = $(filter $(AM_CPPFLAGS:-W%=-Wno-%), \
+    -Wno-shadow -Wno-unused -Wno-cast-qual -Wno-strict-aliasing \
+    -Wno-reorder -Wno-maybe-uninitialized, -Wno-narrowing \
+    -Wno-parentheses)
+
 liblolbullet_a_SOURCES = $(bullet_sources)
-liblolbullet_a_CPPFLAGS = $(AM_CPPFLAGS) -I$(srcdir) \
-    -Wno-extra -Wno-shadow -Wno-unused -Wno-cast-qual -Wno-strict-aliasing \
-    -Wno-parentheses -Wno-reorder
+liblolbullet_a_CPPFLAGS = $(AM_CPPFLAGS) -I$(srcdir) $(disable_cflags)
 
 bullet_sources =