[gentoo-dev] [PATCH 08/11] distutils-r1.eclass: Invert DISTUTILS_USE_PEP517 - backend mapping

["Michał Górny" <mgorny@gentoo.org>]

Invert the eclass logic to map DISTUTILS_USE_PEP517 values to backends
rather than the other way around.  This is in preparation for making
it possible to override the backend used.  One side effect of this
is that in case of DISTUTILS_USE_PEP517 mismatch, we no longer provide
the "correct" value, and only indicate the backend used upstream.

Signed-off-by: Michał Górny <mgorny@gentoo.org>
---
 eclass/distutils-r1.eclass | 122 +++++++++++++++++--------------------
 1 file changed, 56 insertions(+), 66 deletions(-)

diff --git a/eclass/distutils-r1.eclass b/eclass/distutils-r1.eclass
index 2eb6e3208082..0ab42eba1f24 100644
--- a/eclass/distutils-r1.eclass
+++ b/eclass/distutils-r1.eclass
@@ -1064,58 +1064,57 @@ _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>
+# @FUNCTION: _distutils-r1_key_to_backend
+# @USAGE: <key>
 # @INTERNAL
 # @DESCRIPTION:
-# Print the DISTUTILS_USE_PEP517 value corresponding to the backend
-# passed as the only argument.
-_distutils-r1_backend_to_key() {
+# Print the backend corresponding to the DISTUTILS_USE_PEP517 value.
+_distutils-r1_key_to_backend() {
 	debug-print-function ${FUNCNAME} "$@"
 
-	local backend=${1}
-	case ${backend} in
-		flit_core.buildapi|flit.buildapi)
-			echo flit
+	local key=${1}
+	case ${key} in
+		flit)
+			echo flit_core.buildapi
 			;;
-		flit_scm:buildapi)
-			echo flit_scm
+		flit_scm)
+			echo flit_scm:buildapi
 			;;
-		hatchling.build)
-			echo hatchling
+		hatchling)
+			echo hatchling.build
 			;;
-		jupyter_packaging.build_api)
-			echo jupyter
+		jupyter)
+			echo jupyter_packaging.build_api
 			;;
 		maturin)
 			echo maturin
 			;;
-		mesonpy)
-			echo meson-python
+		meson-python)
+			echo mesonpy
 			;;
-		pbr.build)
-			echo pbr
+		pbr)
+			echo pbr.build
 			;;
-		pdm.backend|pdm.pep517.api)
-			echo pdm-backend
+		pdm-backend)
+			echo pdm.backend
 			;;
-		poetry.core.masonry.api|poetry.masonry.api)
-			echo poetry
+		poetry)
+			echo poetry.core.masonry.api
 			;;
-		scikit_build_core.build)
-			echo scikit-build-core
+		scikit-build-core)
+			echo scikit_build_core.build
 			;;
-		setuptools.build_meta|setuptools.build_meta:__legacy__)
-			echo setuptools
+		setuptools)
+			echo setuptools.build_meta
 			;;
-		sipbuild.api)
-			echo sip
+		sip)
+			echo sipbuild.api
 			;;
-		uv_build|uv)
-			echo uv-build
+		uv-build)
+			echo uv_build
 			;;
 		*)
-			die "Unknown backend: ${backend}"
+			die "Unknown DISTUTILS_USE_PEP517 key: ${key}"
 			;;
 	esac
 }
@@ -1150,48 +1149,39 @@ _distutils-r1_get_backend() {
 		return
 	fi
 
-	# verify whether DISTUTILS_USE_PEP517 was set correctly
-	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
-
-	# fix deprecated backends up
-	local new_backend=
-	case ${build_backend} in
-		flit.buildapi)
-			new_backend=flit_core.buildapi
-			;;
-		pdm.pep517.api)
-			new_backend=pdm.backend
-			;;
-		poetry.masonry.api)
-			new_backend=poetry.core.masonry.api
-			;;
-		setuptools.build_meta:__legacy__)
-			# this backend should only be used as implicit fallback
-			new_backend=setuptools.build_meta
-			;;
-		uv)
-			new_backend=uv_build
-			;;
-	esac
+	# get the preferred backend from the eclass
+	local backend_to_use=$(_distutils-r1_key_to_backend "${DISTUTILS_USE_PEP517}")
+	if [[ ${backend_to_use} != ${build_backend} ]]; then
+		# special-case deprecated backends
+		case ${build_backend} in
+			flit.buildapi)
+				;;
+			pdm.pep517.api)
+				;;
+			poetry.masonry.api)
+				;;
+			setuptools.build_meta:__legacy__)
+				;;
+			uv)
+				;;
+			*)
+				eerror "DISTUTILS_USE_PEP517 does not match pyproject.toml!"
+				eerror "  DISTUTILS_USE_PEP517=${DISTUTILS_USE_PEP517}"
+				eerror "  implies backend: ${backend_to_use}"
+				eerror "   pyproject.toml: ${build_backend}"
+				die "DISTUTILS_USE_PEP517 value incorrect"
+		esac
 
-	if [[ -n ${new_backend} ]]; then
+		# if we didn't die, we're dealing with a deprecated backend
 		if [[ ! -f ${T}/.distutils_deprecated_backend_warned ]]; then
 			eqawarn "${build_backend} backend is deprecated.  Please see:"
 			eqawarn "https://projects.gentoo.org/python/guide/qawarn.html#deprecated-pep-517-backends"
-			eqawarn "The eclass will be using ${new_backend} instead."
+			eqawarn "The eclass will be using ${backend_to_use} instead."
 			> "${T}"/.distutils_deprecated_backend_warned || die
 		fi
-		build_backend=${new_backend}
 	fi
 
-	echo "${build_backend}"
+	echo "${backend_to_use}"
 }
 
 # @FUNCTION: distutils_wheel_install