Support PYTHON_DEPEND / PYTHON_BDEPEND in EAPI >=4.
(Patch by Arfrever. Backported from Progress Overlay.)
--- python.eclass
+++ python.eclass
@@ -130,9 +130,37 @@
 
 # @ECLASS-VARIABLE: PYTHON_DEPEND
 # @DESCRIPTION:
-# Specification of dependency on dev-lang/python.
-# Syntax:
-#   PYTHON_DEPEND:             [[!]USE_flag? ]<version_components_group>[ version_components_group]
+# Specification of build time and run time dependency on Python implementational packages.
+#
+# PYTHON_DEPEND in EAPI >=4 is a dependency string with <<>> markers.
+# <<>> markers indicate atoms of Python implementational packages.
+# <<>> markers can contain USE dependencies.
+# <<>> markers must contain versions ranges in ebuilds of packages not supporting installation for multiple Python ABIs.
+#
+# Syntax in EAPI <=3:
+#   PYTHON_DEPEND:             [[!]USE_flag? ]<versions_range>
+#
+# Syntax of versions range:
+#   versions_range:            [[!]USE_flag? ]<version_components_group>[ version_components_group]
+#   version_components_group:  <major_version[:[minimal_version][:maximal_version]]>
+#   major_version:             <2|3|*>
+#   minimal_version:           <minimal_major_version.minimal_minor_version>
+#   maximal_version:           <maximal_major_version.maximal_minor_version>
+
+# @ECLASS-VARIABLE: PYTHON_BDEPEND
+# @DESCRIPTION:
+# Specification of build time dependency on Python implementational packages.
+#
+# PYTHON_BDEPEND in EAPI >=4 is a dependency string with <<>> markers.
+# <<>> markers indicate atoms of Python implementational packages.
+# <<>> markers can contain USE dependencies.
+# <<>> markers must contain versions ranges in ebuilds of packages not supporting installation for multiple Python ABIs.
+#
+# Syntax in EAPI <=3:
+#   PYTHON_BDEPEND:            [[!]USE_flag? ]<versions_range>
+#
+# Syntax of versions range:
+#   versions_range:            [[!]USE_flag? ]<version_components_group>[ version_components_group]
 #   version_components_group:  <major_version[:[minimal_version][:maximal_version]]>
 #   major_version:             <2|3|*>
 #   minimal_version:           <minimal_major_version.minimal_minor_version>
@@ -282,8 +310,172 @@
 	fi
 }
 
+unset _PYTHON_USE_FLAGS_CHECKS_CODE
+
 _python_parse_dependencies_in_new_EAPIs() {
-	:
+	local component cpython_abis=() cpython_atoms=() cpython_reversed_abis=() i input_value input_variable output_value output_variable output_variables PYTHON_ABI replace_whitespace_characters="1" required_USE_flags separate_components USE_dependencies versions_range
+
+	input_value="${!1}"
+	input_variable="$1"
+	output_variables="$2"
+
+	if has "${EAPI:-0}" 4 && _python_package_supporting_installation_for_multiple_python_abis; then
+		cpython_abis=(${_CPYTHON2_GLOBALLY_SUPPORTED_ABIS[@]} ${_CPYTHON3_GLOBALLY_SUPPORTED_ABIS[@]})
+		for ((i = $((${#cpython_abis[@]} - 1)); i >= 0; i--)); do
+			cpython_reversed_abis+=("${cpython_abis[${i}]}")
+		done
+	fi
+
+	_get_matched_USE_dependencies() {
+		local matched_USE_dependencies patterns separate_USE_dependencies USE_dependency
+
+		if [[ -n "${USE_dependencies}" ]]; then
+			separate_USE_dependencies="${USE_dependencies:1:$((${#USE_dependencies} - 2))}"
+			separate_USE_dependencies="${separate_USE_dependencies//,/$'\n'}"
+			while read USE_dependency; do
+				if [[ "${USE_dependency}" == "{"*"}"* ]]; then
+					patterns="${USE_dependency%\}*}"
+					patterns="${patterns:1}"
+					USE_dependency="${USE_dependency#*\}}"
+					if _python_check_python_abi_matching --patterns-list "${PYTHON_ABI}" "${patterns}"; then
+						matched_USE_dependencies+="${matched_USE_dependencies:+,}${USE_dependency}"
+					fi
+				else
+					matched_USE_dependencies+="${matched_USE_dependencies:+,}${USE_dependency}"
+				fi
+			done <<< "${separate_USE_dependencies}"
+			if [[ -n "${matched_USE_dependencies}" ]]; then
+				matched_USE_dependencies="[${matched_USE_dependencies}]"
+			fi
+		fi
+
+		echo "${matched_USE_dependencies}"
+	}
+
+	for ((i = 0; i < "${#input_value}"; i++)); do
+		if [[ "${input_value:${i}:1}" == "<" && "${input_value:$((${i} + 1)):1}" == "<" ]]; then
+			replace_whitespace_characters="0"
+			separate_components+="${input_value:${i}:1}"
+		elif [[ "${input_value:${i}:1}" == ">" && "${input_value:$((${i} + 1)):1}" == ">" ]]; then
+			replace_whitespace_characters="1"
+			separate_components+="${input_value:${i}:1}"
+		elif [[ "${input_value:${i}:1}" == [${IFS}] ]]; then
+			if [[ "${replace_whitespace_characters}" == "1" ]]; then
+				separate_components+=$'\n'
+			else
+				separate_components+="${input_value:${i}:1}"
+			fi
+		else
+			separate_components+="${input_value:${i}:1}"
+		fi
+	done
+
+	while read component; do
+		if [[ -z "${component}" ]]; then
+			continue
+		elif [[ "${component}" == "<<"*">>" ]]; then
+			component="${component:2:$((${#component} - 4))}"
+			if [[ "${component}" == *"["*"]" ]]; then
+				versions_range="${component%%\[*\]}"
+				USE_dependencies="${component#${versions_range}}"
+			else
+				versions_range="${component}"
+				USE_dependencies=""
+			fi
+			if _python_package_supporting_installation_for_multiple_python_abis; then
+				if [[ -n "${versions_range}" ]]; then
+					die "Invalid syntax of ${input_variable}: Versions range cannot be used in ebuilds of packages supporting installation for multiple Python ABIs"
+				fi
+				if has "${EAPI:-0}" 4; then
+					cpython_atoms=()
+					for PYTHON_ABI in "${cpython_reversed_abis[@]}"; do
+						if ! _python_check_python_abi_matching --patterns-list "${PYTHON_ABI}" "${PYTHON_RESTRICTED_ABIS}"; then
+							cpython_atoms+=("dev-lang/python:${PYTHON_ABI}$(_get_matched_USE_dependencies)")
+						fi
+					done
+					if [[ "${#cpython_atoms[@]}" -gt 1 ]]; then
+						output_value+="${output_value:+ }|| ( ${cpython_atoms[@]} )"
+					else
+						output_value+="${output_value:+ }${cpython_atoms[@]}"
+					fi
+					if [[ -z "${USE_dependencies}" ]]; then
+						_PYTHON_USE_FLAGS_CHECKS_CODE+="${_PYTHON_USE_FLAGS_CHECKS_CODE:+ }:;"
+					fi
+				fi
+				for PYTHON_ABI in "${_PYTHON_LOCALLY_SUPPORTED_ABIS[@]}"; do
+					if has "${EAPI:-0}" 4; then
+						if [[ -n "${USE_dependencies}" ]]; then
+							_PYTHON_USE_FLAGS_CHECKS_CODE+="${_PYTHON_USE_FLAGS_CHECKS_CODE:+ }if [[ \"\${PYTHON_ABI}\" == \"${PYTHON_ABI}\" ]] && ! has_version \"\$(python_get_implementational_package)$(_get_matched_USE_dependencies)\"; then die \"\$(python_get_implementational_package)$(_get_matched_USE_dependencies) not installed\"; fi;"
+						fi
+					else
+						if [[ "${PYTHON_ABI}" =~ ^[[:digit:]]+\.[[:digit:]]+$ ]]; then
+							output_value+="${output_value:+ }python_abis_${PYTHON_ABI}? ( dev-lang/python:${PYTHON_ABI}$(_get_matched_USE_dependencies) )"
+						elif [[ "${PYTHON_ABI}" =~ ^[[:digit:]]+\.[[:digit:]]+-jython$ ]]; then
+							output_value+="${output_value:+ }python_abis_${PYTHON_ABI}? ( dev-java/jython:${PYTHON_ABI%-jython}$(_get_matched_USE_dependencies) )"
+						elif [[ "${PYTHON_ABI}" =~ ^[[:digit:]]+\.[[:digit:]]+-pypy-[[:digit:]]+\.[[:digit:]]+$ ]]; then
+							output_value+="${output_value:+ }python_abis_${PYTHON_ABI}? ( dev-python/pypy:${PYTHON_ABI#*-pypy-}$(_get_matched_USE_dependencies) )"
+						fi
+					fi
+				done
+				if ! has "${EAPI:-0}" 4; then
+					if [[ "${#_PYTHON_LOCALLY_SUPPORTED_ABIS[@]}" -gt 1 ]]; then
+						required_USE_flags+="${required_USE_flags:+ }|| ( ${_PYTHON_LOCALLY_SUPPORTED_ABIS[@]/#/python_abis_} )"
+					else
+						required_USE_flags+="${required_USE_flags:+ }${_PYTHON_LOCALLY_SUPPORTED_ABIS[@]/#/python_abis_}"
+					fi
+				fi
+			else
+				_python_parse_versions_range "${versions_range}" "${input_variable}" cpython_atoms
+				cpython_atoms=("${cpython_atoms[@]/%/${USE_dependencies}}")
+				if [[ "${#cpython_atoms[@]}" -gt 1 ]]; then
+					output_value+="${output_value:+ }|| ( ${cpython_atoms[@]} )"
+				else
+					output_value+="${output_value:+ }${cpython_atoms[@]}"
+				fi
+				if [[ -n "${USE_dependencies}" ]]; then
+					_PYTHON_USE_FLAGS_CHECKS_CODE+="${_PYTHON_USE_FLAGS_CHECKS_CODE:+ }if ! has_version \"\$(python_get_implementational_package)${USE_dependencies}\"; then die \"\$(python_get_implementational_package)${USE_dependencies} not installed\"; fi;"
+				else
+					_PYTHON_USE_FLAGS_CHECKS_CODE+="${_PYTHON_USE_FLAGS_CHECKS_CODE:+ }:;"
+				fi
+			fi
+		elif [[ "${component}" == *"?" ]]; then
+			output_value+="${output_value:+ }${component}"
+			required_USE_flags+="${required_USE_flags:+ }${component}"
+			_PYTHON_USE_FLAGS_CHECKS_CODE+="${_PYTHON_USE_FLAGS_CHECKS_CODE:+ }if use ${component%\?};"
+		elif [[ "${component}" == "||" ]]; then
+			if has "${EAPI:-0}" 4 || ! _python_package_supporting_installation_for_multiple_python_abis; then
+				die "Invalid syntax of ${input_variable}: Unrecognized component '${component}'"
+			fi
+			output_value+="${output_value:+ }${component}"
+			required_USE_flags+="${required_USE_flags:+ }${component}"
+		elif [[ "${component}" == "(" ]]; then
+			output_value+="${output_value:+ }${component}"
+			required_USE_flags+="${required_USE_flags:+ }${component}"
+			_PYTHON_USE_FLAGS_CHECKS_CODE+="${_PYTHON_USE_FLAGS_CHECKS_CODE:+ }then"
+		elif [[ "${component}" == ")" ]]; then
+			output_value+="${output_value:+ }${component}"
+			required_USE_flags+="${required_USE_flags:+ }${component}"
+			_PYTHON_USE_FLAGS_CHECKS_CODE+="${_PYTHON_USE_FLAGS_CHECKS_CODE:+ }fi;"
+		else
+			die "Invalid syntax of ${input_variable}: Unrecognized component '${component}'"
+		fi
+	done <<< "${separate_components}"
+
+	for output_variable in ${output_variables}; do
+		eval "${output_variable}+=\"\${!output_variable:+ }\${output_value}\""
+	done
+
+	_PYTHON_USE_FLAGS_CHECKS_CODE="${_PYTHON_USE_FLAGS_CHECKS_CODE%;}"
+
+	if ! has "${EAPI:-0}" 4 && _python_package_supporting_installation_for_multiple_python_abis; then
+		if [[ "${input_variable}" == "PYTHON_DEPEND" ]]; then
+			REQUIRED_USE="${required_USE_flags}"
+		fi
+
+		unset _PYTHON_USE_FLAGS_CHECKS_CODE
+	fi
+
+	unset -f _get_matched_USE_dependencies
 }
 
 DEPEND=">=app-admin/eselect-python-20091230"
@@ -305,7 +497,15 @@
 	fi
 	unset _PYTHON_ATOMS
 else
-	_python_parse_dependencies_in_new_EAPIs
+	if [[ -z "$(declare -p PYTHON_DEPEND 2> /dev/null)" ]] && _python_package_supporting_installation_for_multiple_python_abis; then
+		PYTHON_DEPEND="<<>>"
+	fi
+	if [[ -n "${PYTHON_DEPEND}" ]]; then
+		_python_parse_dependencies_in_new_EAPIs PYTHON_DEPEND "DEPEND RDEPEND"
+	fi
+	if [[ -n "${PYTHON_BDEPEND}" ]]; then
+		_python_parse_dependencies_in_new_EAPIs PYTHON_BDEPEND "DEPEND"
+	fi
 fi
 unset -f _python_parse_versions_range _python_parse_dependencies_in_old_EAPIs _python_parse_dependencies_in_new_EAPIs
 
@@ -523,7 +723,7 @@
 		PYTHON_ABI="${PYTHON_ABI:-$(PYTHON --ABI)}"
 	fi
 
-	if ! has "${EAPI:-0}" 0 1 && [[ -n "${PYTHON_USE_WITH}" || -n "${PYTHON_USE_WITH_OR}" ]]; then
+	if has "${EAPI:-0}" 2 3 && [[ -n "${PYTHON_USE_WITH}" || -n "${PYTHON_USE_WITH_OR}" ]]; then
 		if [[ "${PYTHON_USE_WITH_OPT}" ]]; then
 			if [[ "${PYTHON_USE_WITH_OPT}" == !* ]]; then
 				use ${PYTHON_USE_WITH_OPT#!} && return
@@ -556,6 +756,20 @@
 		}
 
 		if _python_package_supporting_installation_for_multiple_python_abis; then
+			PYTHON_SKIP_SANITY_CHECKS="1" python_execute_function -q python_pkg_setup_check_USE_flags
+		else
+			python_pkg_setup_check_USE_flags
+		fi
+
+		unset -f python_pkg_setup_check_USE_flags
+	fi
+
+	if has "${EAPI:-0}" 4 || { ! has "${EAPI:-0}" 0 1 2 3 4 && ! _python_package_supporting_installation_for_multiple_python_abis; }; then
+		python_pkg_setup_check_USE_flags() {
+			eval "${_PYTHON_USE_FLAGS_CHECKS_CODE}"
+		}
+
+		if _python_package_supporting_installation_for_multiple_python_abis; then
 			PYTHON_SKIP_SANITY_CHECKS="1" python_execute_function -q python_pkg_setup_check_USE_flags
 		else
 			python_pkg_setup_check_USE_flags