Rather than requiring the path to blurb and/or sphinx-build to be specified to the make rule, enhance the Doc/Makefile to look for each first in a virtual environment created by make venv and, if not found, look on the normal process PATH. This allows the Doc/Makefile to take advantage of an installed spinx-build or blurb and, thus, do the right thing most of the time. Also, make the directory for the venv be configurable and document the `make venv` target.
* bpo-30052: Always regenerate cross-references
The patch for bpo-30052 changed the preferred link target
for :func:`bytes` and :func`bytearray` references to be the
respective type definitions rather than the corresponding
builtin function entries.
This patch changes the daily documentation builds to disable
the output caching in Sphinx, in order to ensure that
cross-reference changes like this one are reliably picked
up and applied automatically after merging.
rstlint.py run by "make check" doesn't support Python 2.
"make venv" runs "$(PYTHON) -m venv", whereas Python 2 doens't
provide the venv module: it's a module of Python 3 standard library.
This will create a venv using the interpreter specified by the PYTHON
variable for the Makefile that also install Sphinx. Typical usage is
expected to be:
cd Doc
make venv PYTHON=../python
make html PYTHON=venv/bin/python3
