Current master fails to build PDF documentation

[mouse07410]

MacOS Big Sur 11.6.1, Xcode-13.1, Python-3.9.7 (probably all irrelevant).

Build fails on documentation (so it does not get around to building botan-test):

.  .  .  .  .
clang++ -fstack-protector -m64 -pthread -stdlib=libc++ -march=native build/obj/cli/argon2.o build/obj/cli/asn1.o build/obj/cli/bcrypt.o build/obj/cli/cc_enc.o build/obj/cli/cipher.o build/obj/cli/cli.o build/obj/cli/cli_rng.o build/obj/cli/codec.o build/obj/cli/compress.o build/obj/cli/entropy.o build/obj/cli/hash.o build/obj/cli/hmac.o build/obj/cli/main.o build/obj/cli/math.o build/obj/cli/pbkdf.o build/obj/cli/pk_crypt.o build/obj/cli/psk.o build/obj/cli/pubkey.o build/obj/cli/roughtime.o build/obj/cli/sandbox.o build/obj/cli/speed.o build/obj/cli/timing_tests.o build/obj/cli/tls_client.o build/obj/cli/tls_http_server.o build/obj/cli/tls_proxy.o build/obj/cli/tls_server.o build/obj/cli/tls_utils.o build/obj/cli/tss.o build/obj/cli/utils.o build/obj/cli/x509.o  -L/opt/local/lib/libomp -lomp -L/opt/local/lib  -L. -lbotan-3 -L/opt/local/lib/libomp -lomp -L/opt/local/lib   -lboost_system-mt -lbz2 -lcrypto -ldl -llzma -lsqlite3 -lz -framework CoreFoundation -framework Security  -o botan
"/opt/local/bin/python" "src/scripts/build_docs.py" --build-dir="build"
   INFO: Starting sphinx-build -q -c ./src/configs/sphinx -j 20 -b html ./doc build/docs/handbook
WARNING: while setting up extension sphinx.addnodes: node class 'meta' is already registered, its visitors will be overridden

Extension error:
Could not import extension sphinx.directives.patches (exception: cannot import name 'html' from 'docutils.parsers.rst.directives' (/opt/local/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/docutils/parsers/rst/directives/__init__.py))
  ERROR: Error running sphinx-build -q -c ./src/configs/sphinx -j 20 -b html ./doc build/docs/handbook
make: *** [Makefile:48: build/doc.stamp] Error 1

Configuration: conf-out.txt Failing build: make-out.txt

[mouse07410]

Cleaned everything, rebuilt - problem seems to disappear.