[gentoo-dev] [PATCH v2] distutils-r1.eclass: Implement PEP517 mode

[Michał Górny]

Add a PEP517 mode to the distutils-r1.eclass in order to facilitate
building packages via PEP517 backends.  In order to use it, set
DISTUTILS_USE_PEP517 to the appropriate build system name.  The eclass
will take care of setting BDEPEND, then invoke the backend to build
a wheel and then install its contents in python_compile().  The install
phase is limited to merging the staging area into the image directory.

In PEP517 mode, the test phase is automatically provided with venv-style
install tree that should suffice the vast majority of test suites.
As a result, distutils_install_for_testing should no longer be necessary
and is not available in this mode.

The new mode can also be used to install pre-PEP517 distutils
and setuptools packages.  To do so, just specify setuptools backend.
If pyproject.toml is missing, the eclass assumes legacy setuptools
backend that invokes setup.py.  It also enables setuptools-vendored
distutils, effectively carrying the migration from deprecated stdlib
version.

The PEP517 support effectively deprecates the legacy eclass mode.
This follows upstream deprecation of distutils and install commands
in setuptools.

Signed-off-by: Michał Górny <mgorny@g.o>
---
 eclass/distutils-r1.eclass | 381 ++++++++++++++++++++++++++++---------
 1 file changed, 291 insertions(+), 90 deletions(-)

Changes:

* do not override build paths as pep517 doesn't respect pydistutils.cfg
  and this effectively means it can't find built extensions and builds
  them again

* fix handling legacy packages with pyproject.toml that don't declare
  build-backend

* add more backends (fdm, poetry)

diff --git a/eclass/distutils-r1.eclass b/eclass/distutils-r1.eclass
index ba0226f8fed3..eb8471db8a53 100644
--- a/eclass/distutils-r1.eclass
+++ b/eclass/distutils-r1.eclass
@@ -78,7 +78,35 @@ esac
 # to be exported. It must be run in order for the eclass functions
 # to function properly.
 
+# @ECLASS-VARIABLE: DISTUTILS_USE_PEP517
+# @PRE_INHERIT
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Enable experimental PEP 517 mode for the specified build system.
+# In this mode, the complete build and install is done
+# in python_compile(), venv-style install tree is provided
+# to python_test() and python_install() just merges the temporary
+# install tree into real fs.
+#
+# The variable specifies the build system used.  Currently,
+# the following values are supported:
+#
+# - flit - flit_core backend
+#
+# - pdm - pdm.pep517 backend
+#
+# - poetry - poetry-core backend
+#
+# - setuptools - distutils or setuptools (incl. legacy mode)
+#
+# - standalone - standalone build systems without external deps
+#                (used for bootstrapping).
+#
+# The variable needs to be set before the inherit line.  The eclass
+# adds appropriate build-time dependencies and verifies the value.
+
 # @ECLASS-VARIABLE: DISTUTILS_USE_SETUPTOOLS
+# @DEFAULT_UNSET
 # @PRE_INHERIT
 # @DESCRIPTION:
 # Controls adding dev-python/setuptools dependency.  The allowed values
@@ -97,13 +125,13 @@ esac
 #             (assumes you will take care of doing it correctly)
 #
 # This variable is effective only if DISTUTILS_OPTIONAL is disabled.
-# It needs to be set before the inherit line.
-: ${DISTUTILS_USE_SETUPTOOLS:=bdepend}
+# It is available only in non-PEP517 mode.  It needs to be set before
+# the inherit line.
 
 if [[ ! ${_DISTUTILS_R1} ]]; then
 
 [[ ${EAPI} == 6 ]] && inherit eutils xdg-utils
-inherit multiprocessing toolchain-funcs
+inherit multibuild multiprocessing toolchain-funcs
 
 if [[ ! ${DISTUTILS_SINGLE_IMPL} ]]; then
 	inherit python-r1
@@ -121,25 +149,62 @@ if [[ ! ${_DISTUTILS_R1} ]]; then
 
 _distutils_set_globals() {
 	local rdep bdep
-	local setuptools_dep='>=dev-python/setuptools-42.0.2[${PYTHON_USEDEP}]'
+	if [[ ${DISTUTILS_USE_PEP517} ]]; then
+		if [[ ${DISTUTILS_USE_SETUPTOOLS} ]]; then
+			die "DISTUTILS_USE_SETUPTOOLS is not used in PEP517 mode"
+		fi
 
-	case ${DISTUTILS_USE_SETUPTOOLS} in
-		no|manual)
-			;;
-		bdepend)
-			bdep+=" ${setuptools_dep}"
-			;;
-		rdepend)
-			bdep+=" ${setuptools_dep}"
-			rdep+=" ${setuptools_dep}"
-			;;
-		pyproject.toml)
-			bdep+=' >=dev-python/pyproject2setuppy-22[${PYTHON_USEDEP}]'
-			;;
-		*)
-			die "Invalid DISTUTILS_USE_SETUPTOOLS=${DISTUTILS_USE_SETUPTOOLS}"
-			;;
-	esac
+		# pip is used to install the wheel (TODO: replace with installer
+		# once it finally gets a CLI)
+		# tomli is used to read build-backend from pyproject.toml
+		bdep+='
+			dev-python/pip[${PYTHON_USEDEP}]
+			dev-python/tomli[${PYTHON_USEDEP}]'
+		case ${DISTUTILS_USE_PEP517} in
+			flit)
+				bdep+='
+					dev-python/flit_core[${PYTHON_USEDEP}]'
+				;;
+			pdm)
+				bdep+='
+					dev-python/pdm-pep517[${PYTHON_USEDEP}]'
+				;;
+			poetry)
+				bdep+='
+					dev-python/poetry-core[${PYTHON_USEDEP}]'
+				;;
+			setuptools)
+				bdep+='
+					>=dev-python/setuptools-60.5.0[${PYTHON_USEDEP}]
+					dev-python/wheel[${PYTHON_USEDEP}]'
+				;;
+			standalone)
+				;;
+			*)
+				die "Unknown DISTUTILS_USE_PEP517=${DISTUTILS_USE_PEP517}"
+				;;
+		esac
+	else
+		local setuptools_dep='>=dev-python/setuptools-42.0.2[${PYTHON_USEDEP}]'
+
+		case ${DISTUTILS_USE_SETUPTOOLS:-bdepend} in
+			no|manual)
+				;;
+			bdepend)
+				bdep+=" ${setuptools_dep}"
+				;;
+			rdepend)
+				bdep+=" ${setuptools_dep}"
+				rdep+=" ${setuptools_dep}"
+				;;
+			pyproject.toml)
+				bdep+=' >=dev-python/pyproject2setuppy-22[${PYTHON_USEDEP}]'
+				;;
+			*)
+				die "Invalid DISTUTILS_USE_SETUPTOOLS=${DISTUTILS_USE_SETUPTOOLS}"
+				;;
+		esac
+	fi
 
 	if [[ ! ${DISTUTILS_SINGLE_IMPL} ]]; then
 		bdep=${bdep//\$\{PYTHON_USEDEP\}/${PYTHON_USEDEP}}
@@ -469,7 +534,9 @@ esetup.py() {
 
 	_python_check_EPYTHON
 
-	[[ ${BUILD_DIR} ]] && _distutils-r1_create_setup_cfg
+	if [[ ${BUILD_DIR} && ! ${DISTUTILS_USE_PEP517} ]]; then
+		_distutils-r1_create_setup_cfg
+	fi
 
 	local setup_py=( setup.py )
 	if [[ ${DISTUTILS_USE_SETUPTOOLS} == pyproject.toml ]]; then
@@ -487,7 +554,7 @@ esetup.py() {
 	"${@}" || die -n
 	local ret=${?}
 
-	if [[ ${BUILD_DIR} ]]; then
+	if [[ ${BUILD_DIR} && ! ${DISTUTILS_USE_PEP517} ]]; then
 		rm "${HOME}"/.pydistutils.cfg || die -n
 	fi
 
@@ -525,9 +592,17 @@ esetup.py() {
 #
 # Please note that in order to test the solution properly you need
 # to unmerge the package first.
+#
+# This function is not available in PEP517 mode.  The eclass provides
+# a venv-style install unconditionally therefore, and therefore it
+# should no longer be necessary.
 distutils_install_for_testing() {
 	debug-print-function ${FUNCNAME} "${@}"
 
+	if [[ ${DISTUTILS_USE_PEP517} ]]; then
+		die "${FUNCNAME} is not implemented in PEP517 mode"
+	fi
+
 	# A few notes about --via-home mode:
 	# 1) 'install --home' is terribly broken on pypy, so we need
 	#    to override --install-lib and --install-scripts,
@@ -676,8 +751,10 @@ distutils-r1_python_prepare_all() {
 		fi
 	fi
 
-	_distutils-r1_disable_ez_setup
-	_distutils-r1_handle_pyproject_toml
+	if [[ ! ${DISTUTILS_USE_PEP517} ]]; then
+		_distutils-r1_disable_ez_setup
+		_distutils-r1_handle_pyproject_toml
+	fi
 
 	if [[ ${DISTUTILS_IN_SOURCE_BUILD} && ! ${DISTUTILS_SINGLE_IMPL} ]]
 	then
@@ -721,8 +798,8 @@ _distutils-r1_create_setup_cfg() {
 		zip_safe = False
 	_EOF_
 
-	# we can't refer to ${D} before src_install()
 	if [[ ${EBUILD_PHASE} == install ]]; then
+		# we can't refer to ${D} before src_install()
 		cat >> "${HOME}"/.pydistutils.cfg <<-_EOF_ || die
 
 			# installation paths -- allow calling extra install targets
@@ -734,6 +811,7 @@ _distutils-r1_create_setup_cfg() {
 		_EOF_
 
 		if [[ ! ${DISTUTILS_SINGLE_IMPL} ]]; then
+			# this gets appended to [install]
 			cat >> "${HOME}"/.pydistutils.cfg <<-_EOF_ || die
 				install_scripts = $(python_get_scriptdir)
 			_EOF_
@@ -753,6 +831,35 @@ _distutils-r1_copy_egg_info() {
 	find -name '*.egg-info' -type d -exec cp -R -p {} "${BUILD_DIR}"/ ';' || die
 }
 
+# @FUNCTION: _distutils-r1_backend_to_key
+# @USAGE: <backend>
+# @INTERNAL
+# @DESCRIPTION:
+# Print the DISTUTILS_USE_PEP517 value corresponding to the backend
+# passed as the only argument.
+_distutils-r1_backend_to_key() {
+	debug-print-function ${FUNCNAME} "${@}"
+
+	local backend=${1}
+	case ${backend} in
+		flit_core.buildapi)
+			echo flit
+			;;
+		pdm.pep517.api)
+			echo pdm
+			;;
+		poetry.core.masonry.api)
+			echo poetry
+			;;
+		setuptools.build_meta|setuptools.build_meta:__legacy__)
+			echo setuptools
+			;;
+		*)
+			die "Unknown backend: ${backend}"
+			;;
+	esac
+}
+
 # @FUNCTION: distutils-r1_python_compile
 # @USAGE: [additional-args...]
 # @DESCRIPTION:
@@ -767,16 +874,88 @@ distutils-r1_python_compile() {
 
 	_python_check_EPYTHON
 
-	_distutils-r1_copy_egg_info
+	# call setup.py build when using setuptools (either via PEP517
+	# or in legacy mode)
+	if [[ ${DISTUTILS_USE_PEP517:-setuptools} == setuptools ]]; then
+		_distutils-r1_copy_egg_info
 
-	# distutils is parallel-capable since py3.5
-	local jobs=$(makeopts_jobs "${MAKEOPTS}" INF)
-	if [[ ${jobs} == INF ]]; then
-		local nproc=$(get_nproc)
-		jobs=$(( nproc + 1 ))
+		# distutils is parallel-capable since py3.5
+		local jobs=$(makeopts_jobs "${MAKEOPTS}" INF)
+		if [[ ${jobs} == INF ]]; then
+			local nproc=$(get_nproc)
+			jobs=$(( nproc + 1 ))
+		fi
+
+		esetup.py build -j "${jobs}" "${@}"
 	fi
 
-	esetup.py build -j "${jobs}" "${@}"
+	if [[ ${DISTUTILS_USE_PEP517} ]]; then
+		if [[ -n ${DISTUTILS_ARGS[@]} || -n ${mydistutilsargs[@]} ]]; then
+			die "DISTUTILS_ARGS are not supported in PEP-517 mode"
+		fi
+
+		# python likes to compile any module it sees, which triggers sandbox
+		# failures if some packages haven't compiled their modules yet.
+		addpredict "${EPREFIX}/usr/lib/${EPYTHON}"
+		addpredict /usr/lib/pypy3.8
+		addpredict /usr/lib/portage/pym
+		addpredict /usr/local # bug 498232
+
+		local -x WHEEL_BUILD_DIR=${BUILD_DIR}/wheel
+		mkdir -p "${WHEEL_BUILD_DIR}"
+
+		local build_backend
+		if [[ -f pyproject.toml ]]; then
+			build_backend=$("${EPYTHON}" -c 'import tomli; \
+				print(tomli.load(open("pyproject.toml", "rb")) \
+					["build-system"]["build-backend"])' 2>/dev/null)
+		fi
+		if [[ -z ${build_backend} && ${DISTUTILS_USE_PEP517} == setuptools &&
+			-f setup.py ]]
+		then
+			# use the legacy setuptools backend
+			build_backend=setuptools.build_meta:__legacy__
+		fi
+		[[ -z ${build_backend} ]] &&
+			die "Unable to obtain build-backend from pyproject.toml"
+
+		if [[ ${DISTUTILS_USE_PEP517} != standalone ]]; then
+			local expected_value=$(_distutils-r1_backend_to_key "${build_backend}")
+			if [[ ${DISTUTILS_USE_PEP517} != ${expected_value} ]]; then
+				eerror "DISTUTILS_USE_PEP517 does not match pyproject.toml!"
+				eerror "    have: DISTUTILS_USE_PEP517=${DISTUTILS_USE_PEP517}"
+				eerror "expected: DISTUTILS_USE_PEP517=${expected_value}"
+				eerror "(backend: ${build_backend})"
+				die "DISTUTILS_USE_PEP517 value incorrect"
+			fi
+		fi
+
+		einfo "Building a wheel via ${build_backend}"
+		"${EPYTHON}" -c "import ${build_backend%:*}; \
+			import os; \
+			${build_backend/:/.}.build_wheel(os.environ['WHEEL_BUILD_DIR'])" ||
+			die "Wheel build failed"
+
+		local wheel=( "${WHEEL_BUILD_DIR}"/*.whl )
+		if [[ ${#wheel[@]} -ne 1 ]]; then
+			die "Incorrect number of wheels created (${#wheel[@]}): ${wheel[*]}"
+		fi
+
+		local root=${BUILD_DIR}/install
+		pip install --root "${root}" --no-deps --disable-pip-version-check \
+			--progress-bar off --verbose --ignore-installed \
+			--no-warn-script-location "${wheel}" ||
+			die "pip install failed"
+
+		# enable venv magic inside the install tree
+		mkdir -p "${root}"/usr/bin || die
+		ln -s "${PYTHON}" "${root}/usr/bin/${EPYTHON}" || die
+		ln -s "${EPYTHON}" "${root}/usr/bin/python3" || die
+		ln -s "${EPYTHON}" "${root}/usr/bin/python" || die
+		cat > "${root}"/usr/pyvenv.cfg <<-EOF || die
+			include-system-site-packages = true
+		EOF
+	fi
 }
 
 # @FUNCTION: _distutils-r1_wrap_scripts
@@ -888,59 +1067,74 @@ distutils-r1_python_install() {
 
 	_python_check_EPYTHON
 
-	local root=${D%/}/_${EPYTHON}
-	[[ ${DISTUTILS_SINGLE_IMPL} ]] && root=${D%/}
-
-	# inline DISTUTILS_ARGS logic from esetup.py in order to make
-	# argv overwriting easier
-	local args=(
-		"${DISTUTILS_ARGS[@]}"
-		"${mydistutilsargs[@]}"
-		install --skip-build --root="${root}" "${args[@]}"
-		"${@}"
-	)
-	local DISTUTILS_ARGS=()
-	local mydistutilsargs=()
+	local scriptdir=${EPREFIX}/usr/bin
+	if [[ ${DISTUTILS_USE_PEP517} ]]; then
+		local root=${BUILD_DIR}/install
+		local rscriptdir=${root}$(python_get_scriptdir)
+		[[ -d ${rscriptdir} ]] &&
+			die "${rscriptdir} should not exist!"
+		# remove venv magic
+		rm "${root}"/usr/{pyvenv.cfg,bin/{python,python3,${EPYTHON}}} || die
+		find "${root}"/usr/bin -empty -delete || die
+		if [[ ! ${DISTUTILS_SINGLE_IMPL} && -d ${root}/usr/bin ]]; then
+			mkdir -p "${rscriptdir%/*}" || die
+			mv "${root}/usr/bin" "${rscriptdir}" || die
+		fi
+		python_optimize "${root}$(python_get_sitedir)"
+	else
+		local root=${D%/}/_${EPYTHON}
+		[[ ${DISTUTILS_SINGLE_IMPL} ]] && root=${D%/}
+
+		# inline DISTUTILS_ARGS logic from esetup.py in order to make
+		# argv overwriting easier
+		local args=(
+			"${DISTUTILS_ARGS[@]}"
+			"${mydistutilsargs[@]}"
+			install --skip-build --root="${root}" "${args[@]}"
+			"${@}"
+		)
+		local DISTUTILS_ARGS=()
+		local mydistutilsargs=()
 
-	# enable compilation for the install phase.
-	local -x PYTHONDONTWRITEBYTECODE=
+		# enable compilation for the install phase.
+		local -x PYTHONDONTWRITEBYTECODE=
 
-	# python likes to compile any module it sees, which triggers sandbox
-	# failures if some packages haven't compiled their modules yet.
-	addpredict "${EPREFIX}/usr/lib/${EPYTHON}"
-	addpredict /usr/lib/pypy3.8
-	addpredict /usr/lib/portage/pym
-	addpredict /usr/local # bug 498232
+		# python likes to compile any module it sees, which triggers sandbox
+		# failures if some packages haven't compiled their modules yet.
+		addpredict "${EPREFIX}/usr/lib/${EPYTHON}"
+		addpredict /usr/lib/pypy3.8
+		addpredict /usr/lib/portage/pym
+		addpredict /usr/local # bug 498232
 
-	if [[ ! ${DISTUTILS_SINGLE_IMPL} ]]; then
-		# user may override --install-scripts
-		# note: this is poor but distutils argv parsing is dumb
-		local scriptdir=${EPREFIX}/usr/bin
-
-		# rewrite all the arguments
-		set -- "${args[@]}"
-		args=()
-		while [[ ${@} ]]; do
-			local a=${1}
-			shift
+		if [[ ! ${DISTUTILS_SINGLE_IMPL} ]]; then
+			# user may override --install-scripts
+			# note: this is poor but distutils argv parsing is dumb
+
+			# rewrite all the arguments
+			set -- "${args[@]}"
+			args=()
+			while [[ ${@} ]]; do
+				local a=${1}
+				shift
+
+				case ${a} in
+					--install-scripts=*)
+						scriptdir=${a#--install-scripts=}
+						;;
+					--install-scripts)
+						scriptdir=${1}
+						shift
+						;;
+					*)
+						args+=( "${a}" )
+						;;
+				esac
+			done
+		fi
 
-			case ${a} in
-				--install-scripts=*)
-					scriptdir=${a#--install-scripts=}
-					;;
-				--install-scripts)
-					scriptdir=${1}
-					shift
-					;;
-				*)
-					args+=( "${a}" )
-					;;
-			esac
-		done
+		esetup.py "${args[@]}"
 	fi
 
-	esetup.py "${args[@]}"
-
 	local forbidden_package_names=(
 		examples test tests
 		.pytest_cache .hypothesis
@@ -964,8 +1158,10 @@ distutils-r1_python_install() {
 		die "Package installs 'share' in PyPy prefix, see bug #465546."
 	fi
 
-	if [[ ! ${DISTUTILS_SINGLE_IMPL} ]]; then
+	if [[ ! ${DISTUTILS_SINGLE_IMPL} || ${DISTUTILS_USE_PEP517} ]]; then
 		multibuild_merge_root "${root}" "${D%/}"
+	fi
+	if [[ ! ${DISTUTILS_SINGLE_IMPL} ]]; then
 		_distutils-r1_wrap_scripts "${scriptdir}"
 	fi
 }
@@ -1006,12 +1202,21 @@ distutils-r1_run_phase() {
 		fi
 		local BUILD_DIR=${BUILD_DIR}/build
 	fi
-	local -x PYTHONPATH="${BUILD_DIR}/lib:${PYTHONPATH}"
 
-	# make PATH local for distutils_install_for_testing calls
-	# it makes little sense to let user modify PATH in per-impl phases
-	# and _all() already localizes it
-	local -x PATH=${PATH}
+	if [[ ${DISTUTILS_USE_PEP517} ]]; then
+		local -x PATH=${BUILD_DIR}/install/usr/bin:${PATH}
+	else
+		local -x PYTHONPATH="${BUILD_DIR}/lib:${PYTHONPATH}"
+
+		# make PATH local for distutils_install_for_testing calls
+		# it makes little sense to let user modify PATH in per-impl phases
+		# and _all() already localizes it
+		local -x PATH=${PATH}
+
+		# Undo the default switch in setuptools-60+ for the time being,
+		# to avoid replacing .egg-info file with directory in-place.
+		local -x SETUPTOOLS_USE_DISTUTILS="${SETUPTOOLS_USE_DISTUTILS:-stdlib}"
+	fi
 
 	# Bug 559644
 	# using PYTHONPATH when the ${BUILD_DIR}/lib is not created yet might lead to
@@ -1037,10 +1242,6 @@ distutils-r1_run_phase() {
 
 	local -x LDSHARED="${CC} ${ldopts}" LDCXXSHARED="${CXX} ${ldopts}"
 
-	# Undo the default switch in setuptools-60+ for the time being,
-	# to avoid replacing .egg-info file with directory in-place.
-	local -x SETUPTOOLS_USE_DISTUTILS="${SETUPTOOLS_USE_DISTUTILS:-stdlib}"
-
 	"${@}"
 
 	cd "${_DISTUTILS_INITIAL_CWD}" || die
-- 
2.34.1