common/hooks/pre-pkg/03-restrict-py3-version: new hook

This hook ensures that any package installing files under ${py3_sitelib}
contain a python3 dependency that is bound to the correct minor version.

common/hooks/pre-pkg/03-restrict-py3-version.sh

@@ -0,0 +1,31 @@
+# vim: set ts=4 sw=4 et:
+#
+# This hook performs the following task:
+# - Identifies any python3 runtime dependencies
+# - If any are found, ensures that the base python3 package is included
+# - Restricts the python3 version to the same minor specified in $py3_ver
+
+hook() {
+    [ -d "${PKGDESTDIR}/${py3_lib}" ] || return 0
+    [ "${pkgname}" = python3 ] && return 0
+
+    local dep rdeps
+    for dep in ${run_depends}; do
+        case "${dep}" in
+            python3 | "python3>"* | "python3<"* | "python3-${py3_ver}"* ) ;;
+            *) rdeps+=( "${dep}" ) ;;
+        esac
+    done
+
+    local minor next_minor
+
+    minor="${py3_ver#3.}"
+    next_minor="$(( "${minor}" + 1 ))" >/dev/null 2>&1 || next_minor=
+
+    if ! [ "${next_minor}" -gt "${minor}" ]; then
+        msg_error 'unable to determine python3 minor bounds from $py3_ver\n'
+    fi
+
+    rdeps+=( "python3>=3.${minor}.0_1<3.${next_minor}.0_1" )
+    run_depends="${rdeps[*]}"
+}