makefile: use Python 3 by default (BC)

This change is long overdue IMO.

.. bc::

   Makefile now uses `python3` instead of `python` by default on
   non-Windows platforms. This means Mercurial will be built and
   run with Python 3 instead of Python 2.7 by default.

   To continue using Python 2, set the PYTHON variable. e.g.
   `make install PYTHON=python2.7`.

Differential Revision: https://phab.mercurial-scm.org/D7258

Makefile

@@ -1,258 +1,267 b''
 # If you want to change PREFIX, do not just edit it below. The changed
 # value wont get passed on to recursive make calls. You should instead
 # override the variable on the command like:
 #
 # % make PREFIX=/opt/ install
 
 export PREFIX=/usr/local
+
+# Default to Python 3.
+#
+# Windows ships Python 3 as `python.exe`.
+ifeq ($(OS),Windows_NT)
 PYTHON?=python
+else
+PYTHON?=python3
+endif
+
 $(eval HGROOT := $(shell pwd))
 HGPYTHONS ?= $(HGROOT)/build/pythons
 PURE=
 PYFILESCMD=find mercurial hgext doc -name '*.py'
 PYFILES:=$(shell $(PYFILESCMD))
 DOCFILES=mercurial/helptext/*.txt
 export LANGUAGE=C
 export LC_ALL=C
 TESTFLAGS ?= $(shell echo $$HGTESTFLAGS)
 OSXVERSIONFLAGS ?= $(shell echo $$OSXVERSIONFLAGS)
 CARGO = cargo
 
 # Set this to e.g. "mingw32" to use a non-default compiler.
 COMPILER=
 
 COMPILERFLAG_tmp_ =
 COMPILERFLAG_tmp_${COMPILER} ?= -c $(COMPILER)
 COMPILERFLAG=${COMPILERFLAG_tmp_${COMPILER}}
 
 help:
 	@echo 'Commonly used make targets:'
 	@echo '  all          - build program and documentation'
 	@echo '  install      - install program and man pages to $$PREFIX ($(PREFIX))'
 	@echo '  install-home - install with setup.py install --home=$$HOME ($(HOME))'
 	@echo '  local        - build for inplace usage'
 	@echo '  tests        - run all tests in the automatic test suite'
 	@echo '  test-foo     - run only specified tests (e.g. test-merge1.t)'
 	@echo '  dist         - run all tests and create a source tarball in dist/'
 	@echo '  clean        - remove files created by other targets'
 	@echo '                 (except installed files or dist source tarball)'
 	@echo '  update-pot   - update i18n/hg.pot'
 	@echo
 	@echo 'Example for a system-wide installation under /usr/local:'
 	@echo '  make all && su -c "make install" && hg version'
 	@echo
 	@echo 'Example for a local installation (usable in this directory):'
 	@echo '  make local && ./hg version'
 
 all: build doc
 
 local:
 	$(PYTHON) setup.py $(PURE) \
 	  build_py -c -d . \
 	  build_ext $(COMPILERFLAG) -i \
 	  build_hgexe $(COMPILERFLAG) -i \
 	  build_mo
 	env HGRCPATH= $(PYTHON) hg version
 
 build:
 	$(PYTHON) setup.py $(PURE) build $(COMPILERFLAG)
 
 wheel:
 	FORCE_SETUPTOOLS=1 $(PYTHON) setup.py $(PURE) bdist_wheel $(COMPILERFLAG)
 
 doc:
 	$(MAKE) -C doc
 
 cleanbutpackages:
 	rm -f hg.exe
 	-$(PYTHON) setup.py clean --all # ignore errors from this command
 	find contrib doc hgext hgext3rd i18n mercurial tests hgdemandimport \
 		\( -name '*.py[cdo]' -o -name '*.so' \) -exec rm -f '{}' ';'
 	rm -f MANIFEST MANIFEST.in hgext/__index__.py tests/*.err
 	rm -f mercurial/__modulepolicy__.py
 	if test -d .hg; then rm -f mercurial/__version__.py; fi
 	rm -rf build mercurial/locale
 	$(MAKE) -C doc clean
 	$(MAKE) -C contrib/chg distclean
 	rm -rf rust/target
 	rm -f mercurial/rustext.so
 
 clean: cleanbutpackages
 	rm -rf packages
 
 install: install-bin install-doc
 
 install-bin: build
 	$(PYTHON) setup.py $(PURE) install --root="$(DESTDIR)/" --prefix="$(PREFIX)" --force
 
 install-doc: doc
 	cd doc && $(MAKE) $(MFLAGS) install
 
 install-home: install-home-bin install-home-doc
 
 install-home-bin: build
 	$(PYTHON) setup.py $(PURE) install --home="$(HOME)" --prefix="" --force
 
 install-home-doc: doc
 	cd doc && $(MAKE) $(MFLAGS) PREFIX="$(HOME)" install
 
 MANIFEST-doc:
 	$(MAKE) -C doc MANIFEST
 
 MANIFEST.in: MANIFEST-doc
 	hg manifest | sed -e 's/^/include /' > MANIFEST.in
 	echo include mercurial/__version__.py >> MANIFEST.in
 	sed -e 's/^/include /' < doc/MANIFEST >> MANIFEST.in
 
 dist:	tests dist-notests
 
 dist-notests:	doc MANIFEST.in
 	TAR_OPTIONS="--owner=root --group=root --mode=u+w,go-w,a+rX-s" $(PYTHON) setup.py -q sdist
 
 check: tests
 
 tests:
         # Run Rust tests if cargo is installed
 	if command -v $(CARGO) >/dev/null 2>&1; then \
 		$(MAKE) rust-tests; \
 	fi
 	cd tests && $(PYTHON) run-tests.py $(TESTFLAGS)
 
 test-%:
 	cd tests && $(PYTHON) run-tests.py $(TESTFLAGS) $@
 
 testpy-%:
 	@echo Looking for Python $* in $(HGPYTHONS)
 	[ -e $(HGPYTHONS)/$*/bin/python ] || ( \
 	cd $$(mktemp --directory --tmpdir) && \
         $(MAKE) -f $(HGROOT)/contrib/Makefile.python PYTHONVER=$* PREFIX=$(HGPYTHONS)/$* python )
 	cd tests && $(HGPYTHONS)/$*/bin/python run-tests.py $(TESTFLAGS)
 
 rust-tests: py_feature = $(shell $(PYTHON) -c \
  'import sys; print(["python27-bin", "python3-bin"][sys.version_info[0] >= 3])')
 rust-tests:
 	cd $(HGROOT)/rust/hg-cpython \
 		&& $(CARGO) test --quiet --all \
 			--no-default-features --features "$(py_feature) $(HG_RUST_FEATURES)"
 
 check-code:
 	hg manifest | xargs python contrib/check-code.py
 
 format-c:
 	clang-format --style file -i \
 	  `hg files 'set:(**.c or **.cc or **.h) and not "listfile:contrib/clang-format-ignorelist"'`
 
 update-pot: i18n/hg.pot
 
 i18n/hg.pot: $(PYFILES) $(DOCFILES) i18n/posplit i18n/hggettext
 	$(PYTHON) i18n/hggettext mercurial/commands.py \
 	  hgext/*.py hgext/*/__init__.py \
 	  mercurial/fileset.py mercurial/revset.py \
 	  mercurial/templatefilters.py \
 	  mercurial/templatefuncs.py \
 	  mercurial/templatekw.py \
 	  mercurial/filemerge.py \
 	  mercurial/hgweb/webcommands.py \
 	  mercurial/util.py \
 	  $(DOCFILES) > i18n/hg.pot.tmp
         # All strings marked for translation in Mercurial contain
         # ASCII characters only. But some files contain string
         # literals like this '\037\213'. xgettext thinks it has to
         # parse them even though they are not marked for translation.
         # Extracting with an explicit encoding of ISO-8859-1 will make
         # xgettext "parse" and ignore them.
 	$(PYFILESCMD) | xargs \
 	  xgettext --package-name "Mercurial" \
 	  --msgid-bugs-address "<[e-mail]>" \
 	  --copyright-holder "Matt Mackall <[e-mail]> and others" \
 	  --from-code ISO-8859-1 --join --sort-by-file --add-comments=i18n: \
 	  -d hg -p i18n -o hg.pot.tmp
 	$(PYTHON) i18n/posplit i18n/hg.pot.tmp
         # The target file is not created before the last step. So it never is in
         # an intermediate state.
 	mv -f i18n/hg.pot.tmp i18n/hg.pot
 
 %.po: i18n/hg.pot
         # work on a temporary copy for never having a half completed target
 	cp $@ $@.tmp
 	msgmerge --no-location --update $@.tmp $^
 	mv -f $@.tmp $@
 
 # Packaging targets
 
 packaging_targets := \
   centos5 \
   centos6 \
   centos7 \
   centos8 \
   deb \
   docker-centos5 \
   docker-centos6 \
   docker-centos7 \
   docker-centos8 \
   docker-debian-bullseye \
   docker-debian-buster \
   docker-debian-stretch \
   docker-fedora \
   docker-ubuntu-trusty \
   docker-ubuntu-trusty-ppa \
   docker-ubuntu-xenial \
   docker-ubuntu-xenial-ppa \
   docker-ubuntu-artful \
   docker-ubuntu-artful-ppa \
   docker-ubuntu-bionic \
   docker-ubuntu-bionic-ppa \
   fedora \
   linux-wheels \
   linux-wheels-x86_64 \
   linux-wheels-i686 \
   ppa
 
 # Forward packaging targets for convenience.
 $(packaging_targets):
 	$(MAKE) -C contrib/packaging $@
 
 osx:
 	rm -rf build/mercurial
 	/usr/bin/python2.7 setup.py install --optimize=1 \
 	  --root=build/mercurial/ --prefix=/usr/local/ \
 	  --install-lib=/Library/Python/2.7/site-packages/
 	make -C doc all install DESTDIR="$(PWD)/build/mercurial/"
         # Place a bogon .DS_Store file in the target dir so we can be
         # sure it doesn't get included in the final package.
 	touch build/mercurial/.DS_Store
         # install zsh completions - this location appears to be
         # searched by default as of macOS Sierra.
 	install -d build/mercurial/usr/local/share/zsh/site-functions/
 	install -m 0644 contrib/zsh_completion build/mercurial/usr/local/share/zsh/site-functions/_hg
         # install bash completions - there doesn't appear to be a
         # place that's searched by default for bash, so we'll follow
         # the lead of Apple's git install and just put it in a
         # location of our own.
 	install -d build/mercurial/usr/local/hg/contrib/
 	install -m 0644 contrib/bash_completion build/mercurial/usr/local/hg/contrib/hg-completion.bash
 	make -C contrib/chg \
 	  HGPATH=/usr/local/bin/hg \
 	  PYTHON=/usr/bin/python2.7 \
 	  DESTDIR=../../build/mercurial \
 	  PREFIX=/usr/local \
 	  clean install
 	mkdir -p $${OUTPUTDIR:-dist}
 	HGVER=$$(python contrib/genosxversion.py $(OSXVERSIONFLAGS) build/mercurial/Library/Python/2.7/site-packages/mercurial/__version__.py) && \
 	OSXVER=$$(sw_vers -productVersion | cut -d. -f1,2) && \
 	pkgbuild --filter \\.DS_Store --root build/mercurial/ \
 	  --identifier org.mercurial-scm.mercurial \
 	  --version "$${HGVER}" \
 	  build/mercurial.pkg && \
 	productbuild --distribution contrib/packaging/macosx/distribution.xml \
 	  --package-path build/ \
 	  --version "$${HGVER}" \
 	  --resources contrib/packaging/macosx/ \
 	  "$${OUTPUTDIR:-dist/}"/Mercurial-"$${HGVER}"-macosx"$${OSXVER}".pkg
 
 .PHONY: help all local build doc cleanbutpackages clean install install-bin \
 	install-doc install-home install-home-bin install-home-doc \
 	dist dist-notests check tests rust-tests check-code format-c \
 	update-pot \
 	$(packaging_targets) \
 	osx