Index: configure.ac
===================================================================
RCS file: /cvsroot/curl/curl/configure.ac,v
retrieving revision 1.453
diff -u -r1.453 configure.ac
--- configure.ac	2 Mar 2010 22:02:56 -0000	1.453
+++ configure.ac	5 Mar 2010 17:38:00 -0000
@@ -2380,7 +2380,10 @@
   *)
        AC_MSG_CHECKING([whether $CC supports it])
        if test "$GCC" = yes ; then
-         if $CC --help --verbose 2>&1 | grep fvisibility= > /dev/null ; then
+         if $CC --help --verbose 2>&1 | grep fvisibility= > /dev/null ||
+           dnl clang always supports -fvisibility= but it doesn't show up
+           dnl under --help.
+           test "$compiler_id" = "CLANG"; then
            AC_MSG_RESULT(yes)
            AC_DEFINE(CURL_HIDDEN_SYMBOLS, 1, [to enable hidden symbols])
            AC_DEFINE(CURL_EXTERN_SYMBOL, [__attribute__ ((visibility ("default")))], [to make a symbol visible])
Index: ares/m4/cares-compilers.m4
===================================================================
RCS file: /cvsroot/curl/curl/ares/m4/cares-compilers.m4,v
retrieving revision 1.63
diff -u -r1.63 cares-compilers.m4
--- ares/m4/cares-compilers.m4	16 Nov 2009 23:01:37 -0000	1.63
+++ ares/m4/cares-compilers.m4	5 Mar 2010 17:38:00 -0000
@@ -40,6 +40,7 @@
   CARES_CHECK_COMPILER_HPUX_C
   CARES_CHECK_COMPILER_IBM_C
   CARES_CHECK_COMPILER_INTEL_C
+  CARES_CHECK_COMPILER_CLANG
   CARES_CHECK_COMPILER_GNU_C
   CARES_CHECK_COMPILER_LCC
   CARES_CHECK_COMPILER_SGI_MIPSPRO_C
@@ -66,6 +67,40 @@
 ])
 
 
+dnl CARES_CHECK_COMPILER_CLANG
+dnl -------------------------------------------------
+dnl Verify if compiler being used is clang.
+
+AC_DEFUN([CARES_CHECK_COMPILER_CLANG], [
+  AC_BEFORE([$0],[CARES_CHECK_COMPILER_GNU_C])dnl
+  AC_MSG_CHECKING([if compiler is clang])
+  CURL_CHECK_DEF([__clang__], [], [silent])
+  if test "$curl_cv_have_def___clang__" = "yes"; then
+    AC_MSG_RESULT([yes])
+    compiler_id="CLANG"
+    clangver=`$CC -dumpversion`
+    clangvhi=`echo $clangver | cut -d . -f1`
+    clangvlo=`echo $clangver | cut -d . -f2`
+    compiler_num=`(expr $clangvhi "*" 100 + $clangvlo) 2>/dev/null`
+    flags_dbg_all="-g -g0 -g1 -g2 -g3"
+    flags_dbg_all="$flags_dbg_all -ggdb"
+    flags_dbg_all="$flags_dbg_all -gstabs"
+    flags_dbg_all="$flags_dbg_all -gstabs+"
+    flags_dbg_all="$flags_dbg_all -gcoff"
+    flags_dbg_all="$flags_dbg_all -gxcoff"
+    flags_dbg_all="$flags_dbg_all -gdwarf-2"
+    flags_dbg_all="$flags_dbg_all -gvms"
+    flags_dbg_yes="-g"
+    flags_dbg_off="-g0"
+    flags_opt_all="-O -O0 -O1 -O2 -Os -O3 -O4"
+    flags_opt_yes="-Os"
+    flags_opt_off="-O0"
+  else
+    AC_MSG_RESULT([no])
+  fi
+])
+
+
 dnl CARES_CHECK_COMPILER_DEC_C
 dnl -------------------------------------------------
 dnl Verify if compiler being used is DEC C.
@@ -96,6 +131,7 @@
 
 AC_DEFUN([CARES_CHECK_COMPILER_GNU_C], [
   AC_REQUIRE([CARES_CHECK_COMPILER_INTEL_C])dnl
+  AC_REQUIRE([CARES_CHECK_COMPILER_CLANG])dnl
   AC_MSG_CHECKING([if compiler is GNU C])
   CURL_CHECK_DEF([__GNUC__], [], [silent])
   if test "$curl_cv_have_def___GNUC__" = "yes" &&
@@ -495,7 +531,8 @@
   #
   if test "$compiler_id" != "unknown"; then
     #
-    if test "$compiler_id" = "GNU_C"; then
+    if test "$compiler_id" = "GNU_C" ||
+      test "$compiler_id" = "CLANG"; then
       CARES_CONVERT_INCLUDE_TO_ISYSTEM
     fi
     #
@@ -506,6 +543,14 @@
     #
     case "$compiler_id" in
         #
+      CLANG)
+        #
+        dnl Disable warnings for unused arguments, otherwise clang will
+        dnl warn about compile-time arguments used during link-time, like
+        dnl -O and -g and -pedantic.
+        tmp_CFLAGS="$tmp_CFLAGS -Qunused-arguments"
+        ;;
+        #
       DEC_C)
         #
         dnl Select strict ANSI C compiler mode
@@ -786,6 +831,31 @@
     #
     case "$compiler_id" in
         #
+      CLANG)
+        #
+        if test "$want_warnings" = "yes"; then
+          dnl All versions of clang support the same warnings as at least
+          dnl gcc 4.2.1.
+          tmp_CFLAGS="$tmp_CFLAGS -pedantic"
+          tmp_CFLAGS="$tmp_CFLAGS -Wall -Wextra"
+          tmp_CFLAGS="$tmp_CFLAGS -Wpointer-arith -Wwrite-strings"
+          tmp_CFLAGS="$tmp_CFLAGS -Wunused -Wshadow"
+          tmp_CFLAGS="$tmp_CFLAGS -Winline -Wnested-externs"
+          tmp_CFLAGS="$tmp_CFLAGS -Wmissing-declarations"
+          tmp_CFLAGS="$tmp_CFLAGS -Wmissing-prototypes"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-long-long"
+          tmp_CFLAGS="$tmp_CFLAGS -Wfloat-equal"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-multichar -Wsign-compare"
+          tmp_CFLAGS="$tmp_CFLAGS -Wundef"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-format-nonliteral"
+          tmp_CFLAGS="$tmp_CFLAGS -Wendif-labels -Wstrict-prototypes"
+          tmp_CFLAGS="$tmp_CFLAGS -Wdeclaration-after-statement"
+          tmp_CFLAGS="$tmp_CFLAGS -Wcast-align"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-system-headers"
+          tmp_CFLAGS="$tmp_CFLAGS -Wshorten-64-to-32"
+        fi
+        ;;
+        #
       DEC_C)
         #
         if test "$want_warnings" = "yes"; then
@@ -1326,6 +1396,12 @@
   tmp_CFLAGS=""
   tmp_EXTERN=""
   case "$compiler_id" in
+    CLANG)
+      dnl All versions of clang support -fvisibility=
+      tmp_EXTERN="__attribute__ ((visibility (\"default\")))"
+      tmp_CFLAGS="-fvisibility=hidden"
+      supports_symbol_hiding="yes"
+      ;;
     GNU_C)
       dnl Only gcc 3.4 or later
       if test "$compiler_num" -ge "304"; then
Index: m4/curl-compilers.m4
===================================================================
RCS file: /cvsroot/curl/curl/m4/curl-compilers.m4,v
retrieving revision 1.53
diff -u -r1.53 curl-compilers.m4
--- m4/curl-compilers.m4	17 Jun 2009 02:26:40 -0000	1.53
+++ m4/curl-compilers.m4	5 Mar 2010 17:38:00 -0000
@@ -45,6 +45,7 @@
   CURL_CHECK_COMPILER_HPUX_C
   CURL_CHECK_COMPILER_IBM_C
   CURL_CHECK_COMPILER_INTEL_C
+  CURL_CHECK_COMPILER_CLANG
   CURL_CHECK_COMPILER_GNU_C
   CURL_CHECK_COMPILER_LCC
   CURL_CHECK_COMPILER_SGI_MIPSPRO_C
@@ -71,6 +72,40 @@
 ])
 
 
+dnl CURL_CHECK_COMPILER_CLANG
+dnl -------------------------------------------------
+dnl Verify if compiler being used is clang.
+
+AC_DEFUN([CURL_CHECK_COMPILER_CLANG], [
+  AC_BEFORE([$0],[CURL_CHECK_COMPILER_GNU_C])dnl
+  AC_MSG_CHECKING([if compiler is clang])
+  CURL_CHECK_DEF([__clang__], [], [silent])
+  if test "$curl_cv_have_def___clang__" = "yes"; then
+    AC_MSG_RESULT([yes])
+    compiler_id="CLANG"
+    clangver=`$CC -dumpversion`
+    clangvhi=`echo $clangver | cut -d . -f1`
+    clangvlo=`echo $clangver | cut -d . -f2`
+    compiler_num=`(expr $clangvhi "*" 100 + $clangvlo) 2>/dev/null`
+    flags_dbg_all="-g -g0 -g1 -g2 -g3"
+    flags_dbg_all="$flags_dbg_all -ggdb"
+    flags_dbg_all="$flags_dbg_all -gstabs"
+    flags_dbg_all="$flags_dbg_all -gstabs+"
+    flags_dbg_all="$flags_dbg_all -gcoff"
+    flags_dbg_all="$flags_dbg_all -gxcoff"
+    flags_dbg_all="$flags_dbg_all -gdwarf-2"
+    flags_dbg_all="$flags_dbg_all -gvms"
+    flags_dbg_yes="-g"
+    flags_dbg_off="-g0"
+    flags_opt_all="-O -O0 -O1 -O2 -Os -O3 -O4"
+    flags_opt_yes="-Os"
+    flags_opt_off="-O0"
+  else
+    AC_MSG_RESULT([no])
+  fi
+])
+
+
 dnl CURL_CHECK_COMPILER_DEC_C
 dnl -------------------------------------------------
 dnl Verify if compiler being used is DEC C.
@@ -101,6 +136,7 @@
 
 AC_DEFUN([CURL_CHECK_COMPILER_GNU_C], [
   AC_REQUIRE([CURL_CHECK_COMPILER_INTEL_C])dnl
+  AC_REQUIRE([CURL_CHECK_COMPILER_CLANG])dnl
   AC_MSG_CHECKING([if compiler is GNU C])
   CURL_CHECK_DEF([__GNUC__], [], [silent])
   if test "$curl_cv_have_def___GNUC__" = "yes" &&
@@ -500,7 +536,8 @@
   #
   if test "$compiler_id" != "unknown"; then
     #
-    if test "$compiler_id" = "GNU_C"; then
+    if test "$compiler_id" = "GNU_C" ||
+      test "$compiler_id" = "CLANG"; then
       CURL_CONVERT_INCLUDE_TO_ISYSTEM
     fi
     #
@@ -511,6 +548,14 @@
     #
     case "$compiler_id" in
         #
+      CLANG)
+        #
+        dnl Disable warnings for unused arguments, otherwise clang will
+        dnl warn about compile-time arguments used during link-time, like
+        dnl -O and -g and -pedantic.
+        tmp_CFLAGS="$tmp_CFLAGS -Qunused-arguments"
+        ;;
+        #
       DEC_C)
         #
         dnl Select strict ANSI C compiler mode
@@ -791,6 +836,31 @@
     #
     case "$compiler_id" in
         #
+      CLANG)
+        #
+        if test "$want_warnings" = "yes"; then
+          dnl All versions of clang support the same warnings as at least
+          dnl gcc 4.2.1.
+          tmp_CFLAGS="$tmp_CFLAGS -pedantic"
+          tmp_CFLAGS="$tmp_CFLAGS -Wall -Wextra"
+          tmp_CFLAGS="$tmp_CFLAGS -Wpointer-arith -Wwrite-strings"
+          tmp_CFLAGS="$tmp_CFLAGS -Wunused -Wshadow"
+          tmp_CFLAGS="$tmp_CFLAGS -Winline -Wnested-externs"
+          tmp_CFLAGS="$tmp_CFLAGS -Wmissing-declarations"
+          tmp_CFLAGS="$tmp_CFLAGS -Wmissing-prototypes"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-long-long"
+          tmp_CFLAGS="$tmp_CFLAGS -Wfloat-equal"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-multichar -Wsign-compare"
+          tmp_CFLAGS="$tmp_CFLAGS -Wundef"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-format-nonliteral"
+          tmp_CFLAGS="$tmp_CFLAGS -Wendif-labels -Wstrict-prototypes"
+          tmp_CFLAGS="$tmp_CFLAGS -Wdeclaration-after-statement"
+          tmp_CFLAGS="$tmp_CFLAGS -Wcast-align"
+          tmp_CFLAGS="$tmp_CFLAGS -Wno-system-headers"
+          tmp_CFLAGS="$tmp_CFLAGS -Wshorten-64-to-32"
+        fi
+        ;;
+        #
       DEC_C)
         #
         if test "$want_warnings" = "yes"; then