Bug #668 Improve SDK selection

* rename --macosx-sdk to --macos-sdk
* fix --macos-sdk
* if not specified, select latest SDK

configure.ac

@@ -44,27 +44,18 @@ fi
 AC_SUBST(CROSS_ARCH)
 AC_SUBST(CROSS_LD)
 
-dnl ============================================
-dnl MacOSX build and runtime environment options
-dnl ============================================
-
-AC_ARG_WITH(macosx-sdk,
-    AS_HELP_STRING([--with-macosx-sdk],
-        [Use a specific SDK for building.])
-    [
-                          Usage:     --with-macosx-sdk=<version>
-                          e. g.: --with-macosx-sdk=10.8
-    ],
-,)
-
 
 dnl ===========================
 dnl Check OS X SDK and compiler
 dnl ===========================
+AC_ARG_WITH([macos-sdk],
+            [AS_HELP_STRING([--with-macos-sdk=VER],
+                            [Specify the macOS SDK version to use.])]
+)
 
 case "$host_os" in
     darwin*) # Mac OS X or iOS
-        # If no --with-macosx-sdk option is given, look for one
+        # If no --with-macos-sdk option is given, look for the latestq SDK
 
         # The intent is that for "most" Mac-based developers, a suitable
         # SDK will be found automatically without any configure options.
@@ -75,21 +66,49 @@ case "$host_os" in
         # To find a list of available version run `xcodebuild -showsdks`
 
         MULTIARCH=${host_cpu}-${host_os}
+        unset MACOSX_SDK_PATH
+
         AC_MSG_CHECKING([what macOS compiler to use])
 
-        for _macosx_sdk in $with_macosx_sdk 10.8 10.9 10.10 10.11 10.12 10.13 10.14 10.15 10.16 10.17 10.18 10.19 10.20 11.0 11.1 11.2 11.3 11.4 11.5; do
-            MACOSX_SDK_PATH=$(xcrun --sdk macosx${_macosx_sdk} --show-sdk-path 2> /dev/null)
-            if test -d "$MACOSX_SDK_PATH"; then
-                with_macosx_sdk="${_macosx_sdk}"
-                break
-            else
-                MACOSX_SDK_PATH=$(xcode-select -print-path)/Platforms/MacOSX.platform/Developer/SDKs/MacOSX${_macosx_sdk}.sdk
-                if test -d "$MACOSX_SDK_PATH"; then
-                    with_macosx_sdk="${_macosx_sdk}"
-                    break
+        if test -n "$with_macos_sdk"; then
+            MACOSX_SDK_PATH=$(xcrun --sdk macosx${with_macos_sdk} --show-sdk-path 2> /dev/null)
+            if test -z "$MACOSX_SDK_PATH" ; then
+                AC_MSG_ERROR([could not find SDK ${with_macos_sdk} for macos-${MULTIARCH}])
+            fi
+        else
+            MACOSX_SDK_PATH=$(xcrun --show-sdk-path 2> /dev/null)
+            if test -z "$MACOSX_SDK_PATH" ; then
+                dnl could not find a default SDK - search likely SDK versions
+                for _macos_sdk_major in $(seq 15 -1 10); do
+                    for _macos_sdk_minor in $(seq 20 -1 0); do
+                        _macos_sdk_version=$_macos_sdk_major.$_macos_sdk_minor
+                        MACOSX_SDK_PATH=$(xcrun --sdk macosx${_macos_sdk_version} --show-sdk-path 2> /dev/null)
+                        if test -d "$_macos_sdk_path" ; then
+                            break 2
+                        fi
+                    done
+                done
+
+                dnl could not find a default SDK - search disk for the latest SDK
+                if test -z "$MACOSX_SDK_PATH"; then
+                    for _macos_sdk_major in $(seq 15 -1 10); do
+                        for _macos_sdk_minor in $(seq 20 -1 0); do
+                            _macos_sdk_version=$_macos_sdk_major.$_macos_sdk_minor
+                            MACOSX_SDK_PATH=$(xcode-select -print-path)/Platforms/MacOSX.platform/Developer/SDKs/MacOSX${_macos_sdk_version}.sdk
+                            if test -d "$MACOSX_SDK_PATH"; then
+                                break 2
+                            fi
+
+                            MACOSX_SDK_PATH=$(xcode-select -print-path)/SDKs/MacOSX${_macos_sdk_version}.sdk
+                            if test -d "$MACOSX_SDK_PATH"; then
+                                break 2
+                            fi
+                        done
+                    done
                 fi
             fi
-        done
+        fi
+
         if test -d "$MACOSX_SDK_PATH"; then
             CC="$(xcrun -find clang) -m64 -isysroot $MACOSX_SDK_PATH"
             INSTALL_NAME_TOOL=$(xcrun -find install_name_tool)
@@ -98,7 +117,7 @@ case "$host_os" in
             STRIP=$(xcrun -find strip)
             LIBTOOL=$(xcrun -find libtool)
             RANLIB=$(xcrun -find ranlib)
-            AC_MSG_RESULT([$CC])
+            AC_MSG_RESULT([${MACOSX_SDK_PATH}])
         else
             AC_MSG_RESULT([legacy])
         fi