common/hooks: use file for managing provides

python packages use this to automatically generate provides for each
module installed by the package.

common/hooks/pre-pkg/04-generate-provides.sh

@@ -0,0 +1,29 @@
+# vim: set ts=4 sw=4 et:
+#
+# This hook executes the following tasks:
+#	- Generates provides file with provides entries for xbps-create(1)
+
+generate_python_provides() {
+    local py3_bin="${XBPS_MASTERDIR}/usr/bin/python3"
+
+    if [ -z "$nopyprovides" ] && [ -d "${PKGDESTDIR}/${py3_sitelib}" ] && [ -x "${py3_bin}" ]; then
+        PYTHONPATH="${XBPS_MASTERDIR}/${py3_sitelib}-bootstrap" "${py3_bin}" \
+            "${XBPS_COMMONDIR}"/scripts/parse-py-metadata.py \
+            -S "${PKGDESTDIR}/${py3_sitelib}" -v "${pkgver}" provides
+    fi
+}
+
+hook() {
+    local -a _provides=()
+
+    # include explicit values from the template
+    read -r -a _provides <<< "$provides"
+
+    # get the canonical python package names for each python module
+    mapfile -t _provides -O "${#_provides[@]}" < <( generate_python_provides )
+
+    if [ "${#_provides[@]}" -gt 0 ]; then
+        echo "   ${_provides[*]}"
+        echo "${_provides[*]}" > "${XBPS_STATEDIR}/${pkgname}-provides"
+    fi
+}