[gentoo-dev] [PATCH 4/7] distutils-r1.eclass: Support reusing prior wheels when compatible

["Michał Górny" <mgorny@gentoo.org>]

Support reusing the wheels built for earlier Python implementations
if they are compatible with the subsequent implementations being built.
This includes pure Python wheels in packages that do not set
DISTUTILS_EXT, and stable ABI wheels.

Closes: https://bugs.gentoo.org/931689
Signed-off-by: Michał Górny <mgorny@gentoo.org>
---
 eclass/distutils-r1.eclass | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/eclass/distutils-r1.eclass b/eclass/distutils-r1.eclass
index f014a184885a..e4d53083124e 100644
--- a/eclass/distutils-r1.eclass
+++ b/eclass/distutils-r1.eclass
@@ -189,6 +189,18 @@ esac
 #     ${DISTUTILS_DEPS}"
 # @CODE
 
+# @ECLASS_VARIABLE: DISTUTILS_ALLOW_WHEEL_REUSE
+# @DEFAULT_UNSET
+# @USER_VARIABLE
+# @DESCRIPTION:
+# If set to a non-empty value, the eclass is allowed to reuse a wheel
+# that was built for a prior Python implementation, provided that it is
+# compatible with the current one, rather than building a new one.
+#
+# This is an optimization that can avoid the overhead of calling into
+# the build system in pure Python packages and packages using the stable
+# Python ABI.
+
 if [[ -z ${_DISTUTILS_R1_ECLASS} ]]; then
 _DISTUTILS_R1_ECLASS=1
 
@@ -1584,6 +1596,27 @@ distutils-r1_python_compile() {
 	esac
 
 	if [[ ${DISTUTILS_USE_PEP517} ]]; then
+		if [[ ${DISTUTILS_ALLOW_WHEEL_REUSE} ]]; then
+			local whl
+			for whl in "${DISTUTILS_WHEELS[@]}"; do
+				# 1. Use pure Python wheels only if we're not expected
+				# to build extensions.  Otherwise, we may end up
+				# not building the extension at all when e.g. PyPy3
+				# is built without one.
+				#
+				# 2. For CPython, we can reuse stable ABI wheels.  Note
+				# that this relies on the assumption that we're building
+				# from the oldest to the newest implementation,
+				# and the wheels are forward-compatible.
+				if [[ ( ! ${DISTUTILS_EXT} && ${whl} == *py3-none-any* ) ||
+					( ${EPYTHON} == python* && ${whl} == *-abi3-* ) ]]
+				then
+					distutils_wheel_install "${BUILD_DIR}/install" "${whl}"
+					return
+				fi
+			done
+		fi
+
 		distutils_pep517_install "${BUILD_DIR}/install"
 		DISTUTILS_WHEELS+=( "${DISTUTILS_WHEEL_PATH}" )
 	fi
-- 
2.45.1