dev-lang/swift: update LLVM_COMPAT

Updates LLVM_COMPAT to allow building Swift 6 with LLVM/Clang 22, and reintroduces a `libcxx` USE flag to allow dropping a hard dependency on GCC <16 on systems that don't want to use it. Swift 5.10 does not build with Clang 22. Signed-off-by: Itai Ferber <itai@itaiferber.net>
2026-07-08 14:43:27 -04:00 · 2026-07-01 12:53:21 -04:00
parent 80fbc4c2ac
commit 0591ece77d
7 changed files with 227 additions and 42 deletions
--- a/dev-lang/swift/metadata.xml
+++ b/dev-lang/swift/metadata.xml
@@ -8,6 +8,11 @@
  <upstream>
    <remote-id type="github">swiftlang/swift</remote-id>
  </upstream>
+  <use>
+    <flag name="libcxx">
+      Build against <pkg>llvm-runtimes/libcxx</pkg> as the default C++ runtime library over GCC's libdstc++.
+    </flag>
+  </use>
  <slots>
    <slot name="0">
      The original slot for swift-5.10.1; should no longer be used.
--- a/dev-lang/swift/swift-6.0.3-r2.ebuild
+++ b/dev-lang/swift/swift-6.0.3-r2.ebuild
@@ -3,9 +3,9 @@

 EAPI=8

-LLVM_COMPAT=( {17..21} )
+LLVM_COMPAT=( {17..22} )
 PYTHON_COMPAT=( python3_{12..14} )
-inherit flag-o-matic llvm-r2 python-single-r1 toolchain-funcs
+inherit flag-o-matic llvm-r2 python-single-r1

 DESCRIPTION="A high-level, general-purpose, multi-paradigm, compiled programming language"
 HOMEPAGE="https://www.swift.org"
@@ -67,6 +67,7 @@ S="${WORKDIR}"
 LICENSE="Apache-2.0"
 SLOT="6/0"
 KEYWORDS="~amd64"
+IUSE="libcxx"
 REQUIRED_USE="${PYTHON_REQUIRED_USE}"

 RESTRICT="strip"
@@ -85,8 +86,34 @@ RDEPEND="
 	>=virtual/zlib-1.3:=
 	dev-lang/python
 	$(llvm_gen_dep 'llvm-core/lld:${LLVM_SLOT}=')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
 "

+# Adapted from `llvm-r2.eclass`'s `llvm_gen_dep` to output conditional
+# dependency alocks, which isn't currently supported. If llvm-r2 or a future
+# eclass introduces `llvm_gen_cond_dep`, this definition should be dropped in
+# favor of that.
+#
+# Used to conditionally depend on GCC <16 for LLVM_SLOT <22; see `src_configure`
+# for more.
+_swift_llvm_gen_cond_dep() {
+	debug-print-function ${FUNCNAME} "$@"
+
+	[[ $# -ge 2 ]] || die "Usage: ${FUNCNAME} <dependency> <slot>..."
+
+	local dep=${1}
+	shift
+
+	local slot
+	for slot in "${_LLVM_SLOTS[@]}"; do
+		for match in $*; do
+			if [[ "$slot" == "${match}" ]]; then
+				echo "llvm_slot_${slot}? ( ${dep//\$\{LLVM_SLOT\}/${slot}} )"
+			fi
+		done
+	done
+}
+
 BDEPEND="
 	${PYTHON_DEPS}
 	>=dev-build/cmake-3.24.2
@@ -99,7 +126,6 @@ BDEPEND="
 	>=dev-vcs/git-2.39
 	>=sys-apps/coreutils-9
 	>=sys-devel/gcc-11
-	<sys-devel/gcc-16
 	>=sys-libs/ncurses-6
 	>=virtual/zlib-1.3:=
 	|| (
@@ -110,6 +136,8 @@ BDEPEND="
 		llvm-core/clang:${LLVM_SLOT}=
 		llvm-core/lld:${LLVM_SLOT}=
 	')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
+	!libcxx? ( $(_swift_llvm_gen_cond_dep '<sys-devel/gcc-16' {17..21}) )
 	dev-lang/python
 	$(python_gen_cond_dep 'dev-python/setuptools[${PYTHON_USEDEP}]')
 "
@@ -204,14 +232,16 @@ src_configure() {
 		fi
 	fi

-	if [[ "$(tc-get-cxx-stdlib)" = 'libc++' ]]; then
-		# On systems which use libc++ as their default C++ stdlib (e.g. systems
-		# with the LLVM profile), we want to build the internal libc++ and
-		# ensure we link against it.
+	if use libcxx; then
 		extra_build_flags+=(
 			--libcxx
 			--extra-cmake-options=-DCLANG_DEFAULT_CXX_STDLIB=libc++
 		)
+	elif [[ "${LLVM_SLOT}" -ge 22 ]]; then
+		# While `__COUNTER__` is being standardized, Clang 22 considers it a C2Y
+		# extension, and produces compilation errors by default. The semantics
+		# haven't changed, so these can be downgraded to warnings.
+		append-cxxflags '-Wno-error=c2y-extensions'
 	else
 		# Swift is going to be building against GCC's libstdc++ using Clang, and
 		# GCC 16 libstdc++ headers can only be parsed by Clang 22 and later.
--- a/dev-lang/swift/swift-6.1.3.ebuild
+++ b/dev-lang/swift/swift-6.1.3.ebuild
@@ -3,9 +3,9 @@

 EAPI=8

-LLVM_COMPAT=( {17..21} )
+LLVM_COMPAT=( {17..22} )
 PYTHON_COMPAT=( python3_{12..14} )
-inherit flag-o-matic llvm-r2 python-single-r1 toolchain-funcs
+inherit flag-o-matic llvm-r2 python-single-r1

 DESCRIPTION="A high-level, general-purpose, multi-paradigm, compiled programming language"
 HOMEPAGE="https://www.swift.org"
@@ -69,6 +69,7 @@ S="${WORKDIR}"
 LICENSE="Apache-2.0"
 SLOT="6/1"
 KEYWORDS="~amd64"
+IUSE="libcxx"
 REQUIRED_USE="${PYTHON_REQUIRED_USE}"

 RESTRICT="strip"
@@ -87,8 +88,34 @@ RDEPEND="
 	>=virtual/zlib-1.3.1:=
 	dev-lang/python
 	$(llvm_gen_dep 'llvm-core/lld:${LLVM_SLOT}=')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
 "

+# Adapted from `llvm-r2.eclass`'s `llvm_gen_dep` to output conditional
+# dependency alocks, which isn't currently supported. If llvm-r2 or a future
+# eclass introduces `llvm_gen_cond_dep`, this definition should be dropped in
+# favor of that.
+#
+# Used to conditionally depend on GCC <16 for LLVM_SLOT <22; see `src_configure`
+# for more.
+_swift_llvm_gen_cond_dep() {
+	debug-print-function ${FUNCNAME} "$@"
+
+	[[ $# -ge 2 ]] || die "Usage: ${FUNCNAME} <dependency> <slot>..."
+
+	local dep=${1}
+	shift
+
+	local slot
+	for slot in "${_LLVM_SLOTS[@]}"; do
+		for match in $*; do
+			if [[ "$slot" == "${match}" ]]; then
+				echo "llvm_slot_${slot}? ( ${dep//\$\{LLVM_SLOT\}/${slot}} )"
+			fi
+		done
+	done
+}
+
 BDEPEND="
 	${PYTHON_DEPS}
 	>=dev-build/cmake-3.30.2
@@ -101,7 +128,6 @@ BDEPEND="
 	>=dev-vcs/git-2.39
 	>=sys-apps/coreutils-9
 	>=sys-devel/gcc-11
-	<sys-devel/gcc-16
 	>=sys-libs/ncurses-6
 	>=virtual/zlib-1.3.1:=
 	|| (
@@ -112,6 +138,8 @@ BDEPEND="
 		llvm-core/clang:${LLVM_SLOT}=
 		llvm-core/lld:${LLVM_SLOT}=
 	')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
+	!libcxx? ( $(_swift_llvm_gen_cond_dep '<sys-devel/gcc-16' {17..21}) )
 	dev-lang/python
 	$(python_gen_cond_dep 'dev-python/setuptools[${PYTHON_USEDEP}]')
 "
@@ -206,14 +234,16 @@ src_configure() {
 		fi
 	fi

-	if [[ "$(tc-get-cxx-stdlib)" = 'libc++' ]]; then
-		# On systems which use libc++ as their default C++ stdlib (e.g. systems
-		# with the LLVM profile), we want to build the internal libc++ and
-		# ensure we link against it.
+	if use libcxx; then
 		extra_build_flags+=(
 			--libcxx
 			--extra-cmake-options=-DCLANG_DEFAULT_CXX_STDLIB=libc++
 		)
+	elif [[ "${LLVM_SLOT}" -ge 22 ]]; then
+		# While `__COUNTER__` is being standardized, Clang 22 considers it a C2Y
+		# extension, and produces compilation errors by default. The semantics
+		# haven't changed, so these can be downgraded to warnings.
+		append-cxxflags '-Wno-error=c2y-extensions'
 	else
 		# Swift is going to be building against GCC's libstdc++ using Clang, and
 		# GCC 16 libstdc++ headers can only be parsed by Clang 22 and later.
--- a/dev-lang/swift/swift-6.2.4.ebuild
+++ b/dev-lang/swift/swift-6.2.4.ebuild
@@ -3,9 +3,9 @@

 EAPI=8

-LLVM_COMPAT=( {17..21} )
+LLVM_COMPAT=( {17..22} )
 PYTHON_COMPAT=( python3_{12..14} )
-inherit flag-o-matic llvm-r2 python-single-r1 toolchain-funcs
+inherit flag-o-matic llvm-r2 python-single-r1

 DESCRIPTION="A high-level, general-purpose, multi-paradigm, compiled programming language"
 HOMEPAGE="https://www.swift.org"
@@ -70,6 +70,7 @@ S="${WORKDIR}"
 LICENSE="Apache-2.0"
 SLOT="6/2"
 KEYWORDS="~amd64"
+IUSE="libcxx"
 REQUIRED_USE="${PYTHON_REQUIRED_USE}"

 RESTRICT="strip"
@@ -88,8 +89,34 @@ RDEPEND="
 	>=virtual/zlib-1.3.1:=
 	dev-lang/python
 	$(llvm_gen_dep 'llvm-core/lld:${LLVM_SLOT}=')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
 "

+# Adapted from `llvm-r2.eclass`'s `llvm_gen_dep` to output conditional
+# dependency alocks, which isn't currently supported. If llvm-r2 or a future
+# eclass introduces `llvm_gen_cond_dep`, this definition should be dropped in
+# favor of that.
+#
+# Used to conditionally depend on GCC <16 for LLVM_SLOT <22; see `src_configure`
+# for more.
+_swift_llvm_gen_cond_dep() {
+	debug-print-function ${FUNCNAME} "$@"
+
+	[[ $# -ge 2 ]] || die "Usage: ${FUNCNAME} <dependency> <slot>..."
+
+	local dep=${1}
+	shift
+
+	local slot
+	for slot in "${_LLVM_SLOTS[@]}"; do
+		for match in $*; do
+			if [[ "$slot" == "${match}" ]]; then
+				echo "llvm_slot_${slot}? ( ${dep//\$\{LLVM_SLOT\}/${slot}} )"
+			fi
+		done
+	done
+}
+
 BDEPEND="
 	${PYTHON_DEPS}
 	>=dev-build/cmake-3.30.2
@@ -102,7 +129,6 @@ BDEPEND="
 	>=dev-vcs/git-2.39
 	>=sys-apps/coreutils-9
 	>=sys-devel/gcc-11
-	<sys-devel/gcc-16
 	>=sys-libs/ncurses-6
 	>=virtual/zlib-1.3.1:=
 	|| (
@@ -113,6 +139,8 @@ BDEPEND="
 		llvm-core/clang:${LLVM_SLOT}=
 		llvm-core/lld:${LLVM_SLOT}=
 	')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
+	!libcxx? ( $(_swift_llvm_gen_cond_dep '<sys-devel/gcc-16' {17..21}) )
 	dev-lang/python
 	$(python_gen_cond_dep 'dev-python/setuptools[${PYTHON_USEDEP}]')
 "
@@ -207,14 +235,16 @@ src_configure() {
 		fi
 	fi

-	if [[ "$(tc-get-cxx-stdlib)" = 'libc++' ]]; then
-		# On systems which use libc++ as their default C++ stdlib (e.g. systems
-		# with the LLVM profile), we want to build the internal libc++ and
-		# ensure we link against it.
+	if use libcxx; then
 		extra_build_flags+=(
 			--libcxx
 			--extra-cmake-options=-DCLANG_DEFAULT_CXX_STDLIB=libc++
 		)
+	elif [[ "${LLVM_SLOT}" -ge 22 ]]; then
+		# While `__COUNTER__` is being standardized, Clang 22 considers it a C2Y
+		# extension, and produces compilation errors by default. The semantics
+		# haven't changed, so these can be downgraded to warnings.
+		append-cxxflags '-Wno-error=c2y-extensions'
 	else
 		# Swift is going to be building against GCC's libstdc++ using Clang, and
 		# GCC 16 libstdc++ headers can only be parsed by Clang 22 and later.
--- a/dev-lang/swift/swift-6.3-r1.ebuild
+++ b/dev-lang/swift/swift-6.3-r1.ebuild
@@ -3,9 +3,9 @@

 EAPI=8

-LLVM_COMPAT=( {17..21} )
+LLVM_COMPAT=( {17..22} )
 PYTHON_COMPAT=( python3_{12..14} )
-inherit flag-o-matic llvm-r2 python-single-r1 toolchain-funcs
+inherit flag-o-matic llvm-r2 python-single-r1

 DESCRIPTION="A high-level, general-purpose, multi-paradigm, compiled programming language"
 HOMEPAGE="https://www.swift.org"
@@ -72,6 +72,7 @@ S="${WORKDIR}"
 LICENSE="Apache-2.0"
 SLOT="6/3"
 KEYWORDS="~amd64"
+IUSE="libcxx"
 REQUIRED_USE="${PYTHON_REQUIRED_USE}"

 RESTRICT="strip"
@@ -90,8 +91,34 @@ RDEPEND="
 	>=virtual/zlib-1.3.1:=
 	dev-lang/python
 	$(llvm_gen_dep 'llvm-core/lld:${LLVM_SLOT}=')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
 "

+# Adapted from `llvm-r2.eclass`'s `llvm_gen_dep` to output conditional
+# dependency alocks, which isn't currently supported. If llvm-r2 or a future
+# eclass introduces `llvm_gen_cond_dep`, this definition should be dropped in
+# favor of that.
+#
+# Used to conditionally depend on GCC <16 for LLVM_SLOT <22; see `src_configure`
+# for more.
+_swift_llvm_gen_cond_dep() {
+	debug-print-function ${FUNCNAME} "$@"
+
+	[[ $# -ge 2 ]] || die "Usage: ${FUNCNAME} <dependency> <slot>..."
+
+	local dep=${1}
+	shift
+
+	local slot
+	for slot in "${_LLVM_SLOTS[@]}"; do
+		for match in $*; do
+			if [[ "$slot" == "${match}" ]]; then
+				echo "llvm_slot_${slot}? ( ${dep//\$\{LLVM_SLOT\}/${slot}} )"
+			fi
+		done
+	done
+}
+
 BDEPEND="
 	${PYTHON_DEPS}
 	>=dev-build/cmake-3.30.2
@@ -104,7 +131,6 @@ BDEPEND="
 	>=dev-vcs/git-2.39
 	>=sys-apps/coreutils-9
 	>=sys-devel/gcc-11
-	<sys-devel/gcc-16
 	>=sys-libs/ncurses-6
 	>=virtual/zlib-1.3.1:=
 	|| (
@@ -115,6 +141,8 @@ BDEPEND="
 		llvm-core/clang:${LLVM_SLOT}=
 		llvm-core/lld:${LLVM_SLOT}=
 	')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
+	!libcxx? ( $(_swift_llvm_gen_cond_dep '<sys-devel/gcc-16' {17..21}) )
 	dev-lang/python
 	$(python_gen_cond_dep 'dev-python/setuptools[${PYTHON_USEDEP}]')
 "
@@ -209,14 +237,16 @@ src_configure() {
 		fi
 	fi

-	if [[ "$(tc-get-cxx-stdlib)" = 'libc++' ]]; then
-		# On systems which use libc++ as their default C++ stdlib (e.g. systems
-		# with the LLVM profile), we want to build the internal libc++ and
-		# ensure we link against it.
+	if use libcxx; then
 		extra_build_flags+=(
 			--libcxx
 			--extra-cmake-options=-DCLANG_DEFAULT_CXX_STDLIB=libc++
 		)
+	elif [[ "${LLVM_SLOT}" -ge 22 ]]; then
+		# While `__COUNTER__` is being standardized, Clang 22 considers it a C2Y
+		# extension, and produces compilation errors by default. The semantics
+		# haven't changed, so these can be downgraded to warnings.
+		append-cxxflags '-Wno-error=c2y-extensions'
 	else
 		# Swift is going to be building against GCC's libstdc++ using Clang, and
 		# GCC 16 libstdc++ headers can only be parsed by Clang 22 and later.
--- a/dev-lang/swift/swift-6.3.1.ebuild
+++ b/dev-lang/swift/swift-6.3.1.ebuild
@@ -3,9 +3,9 @@

 EAPI=8

-LLVM_COMPAT=( {17..21} )
+LLVM_COMPAT=( {17..22} )
 PYTHON_COMPAT=( python3_{12..14} )
-inherit flag-o-matic llvm-r2 python-single-r1 toolchain-funcs
+inherit flag-o-matic llvm-r2 python-single-r1

 DESCRIPTION="A high-level, general-purpose, multi-paradigm, compiled programming language"
 HOMEPAGE="https://www.swift.org"
@@ -72,6 +72,7 @@ S="${WORKDIR}"
 LICENSE="Apache-2.0"
 SLOT="6/3"
 KEYWORDS="~amd64"
+IUSE="libcxx"
 REQUIRED_USE="${PYTHON_REQUIRED_USE}"

 RESTRICT="strip"
@@ -90,8 +91,34 @@ RDEPEND="
 	>=virtual/zlib-1.3.1:=
 	dev-lang/python
 	$(llvm_gen_dep 'llvm-core/lld:${LLVM_SLOT}=')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
 "

+# Adapted from `llvm-r2.eclass`'s `llvm_gen_dep` to output conditional
+# dependency alocks, which isn't currently supported. If llvm-r2 or a future
+# eclass introduces `llvm_gen_cond_dep`, this definition should be dropped in
+# favor of that.
+#
+# Used to conditionally depend on GCC <16 for LLVM_SLOT <22; see `src_configure`
+# for more.
+_swift_llvm_gen_cond_dep() {
+	debug-print-function ${FUNCNAME} "$@"
+
+	[[ $# -ge 2 ]] || die "Usage: ${FUNCNAME} <dependency> <slot>..."
+
+	local dep=${1}
+	shift
+
+	local slot
+	for slot in "${_LLVM_SLOTS[@]}"; do
+		for match in $*; do
+			if [[ "$slot" == "${match}" ]]; then
+				echo "llvm_slot_${slot}? ( ${dep//\$\{LLVM_SLOT\}/${slot}} )"
+			fi
+		done
+	done
+}
+
 BDEPEND="
 	${PYTHON_DEPS}
 	>=dev-build/cmake-3.30.2
@@ -104,7 +131,6 @@ BDEPEND="
 	>=dev-vcs/git-2.39
 	>=sys-apps/coreutils-9
 	>=sys-devel/gcc-11
-	<sys-devel/gcc-16
 	>=sys-libs/ncurses-6
 	>=virtual/zlib-1.3.1:=
 	|| (
@@ -115,6 +141,8 @@ BDEPEND="
 		llvm-core/clang:${LLVM_SLOT}=
 		llvm-core/lld:${LLVM_SLOT}=
 	')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
+	!libcxx? ( $(_swift_llvm_gen_cond_dep '<sys-devel/gcc-16' {17..21}) )
 	dev-lang/python
 	$(python_gen_cond_dep 'dev-python/setuptools[${PYTHON_USEDEP}]')
 "
@@ -209,14 +237,16 @@ src_configure() {
 		fi
 	fi

-	if [[ "$(tc-get-cxx-stdlib)" = 'libc++' ]]; then
-		# On systems which use libc++ as their default C++ stdlib (e.g. systems
-		# with the LLVM profile), we want to build the internal libc++ and
-		# ensure we link against it.
+	if use libcxx; then
 		extra_build_flags+=(
 			--libcxx
 			--extra-cmake-options=-DCLANG_DEFAULT_CXX_STDLIB=libc++
 		)
+	elif [[ "${LLVM_SLOT}" -ge 22 ]]; then
+		# While `__COUNTER__` is being standardized, Clang 22 considers it a C2Y
+		# extension, and produces compilation errors by default. The semantics
+		# haven't changed, so these can be downgraded to warnings.
+		append-cxxflags '-Wno-error=c2y-extensions'
 	else
 		# Swift is going to be building against GCC's libstdc++ using Clang, and
 		# GCC 16 libstdc++ headers can only be parsed by Clang 22 and later.
--- a/dev-lang/swift/swift-6.3.2.ebuild
+++ b/dev-lang/swift/swift-6.3.2.ebuild
@@ -3,9 +3,9 @@

 EAPI=8

-LLVM_COMPAT=( {17..21} )
+LLVM_COMPAT=( {17..22} )
 PYTHON_COMPAT=( python3_{12..14} )
-inherit flag-o-matic llvm-r2 python-single-r1 toolchain-funcs
+inherit flag-o-matic llvm-r2 python-single-r1

 DESCRIPTION="A high-level, general-purpose, multi-paradigm, compiled programming language"
 HOMEPAGE="https://www.swift.org"
@@ -72,6 +72,7 @@ S="${WORKDIR}"
 LICENSE="Apache-2.0"
 SLOT="6/3"
 KEYWORDS="~amd64"
+IUSE="libcxx"
 REQUIRED_USE="${PYTHON_REQUIRED_USE}"

 RESTRICT="strip"
@@ -90,8 +91,34 @@ RDEPEND="
 	>=virtual/zlib-1.3.1:=
 	dev-lang/python
 	$(llvm_gen_dep 'llvm-core/lld:${LLVM_SLOT}=')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
 "

+# Adapted from `llvm-r2.eclass`'s `llvm_gen_dep` to output conditional
+# dependency alocks, which isn't currently supported. If llvm-r2 or a future
+# eclass introduces `llvm_gen_cond_dep`, this definition should be dropped in
+# favor of that.
+#
+# Used to conditionally depend on GCC <16 for LLVM_SLOT <22; see `src_configure`
+# for more.
+_swift_llvm_gen_cond_dep() {
+	debug-print-function ${FUNCNAME} "$@"
+
+	[[ $# -ge 2 ]] || die "Usage: ${FUNCNAME} <dependency> <slot>..."
+
+	local dep=${1}
+	shift
+
+	local slot
+	for slot in "${_LLVM_SLOTS[@]}"; do
+		for match in $*; do
+			if [[ "$slot" == "${match}" ]]; then
+				echo "llvm_slot_${slot}? ( ${dep//\$\{LLVM_SLOT\}/${slot}} )"
+			fi
+		done
+	done
+}
+
 BDEPEND="
 	${PYTHON_DEPS}
 	>=dev-build/cmake-3.30.2
@@ -104,7 +131,6 @@ BDEPEND="
 	>=dev-vcs/git-2.39
 	>=sys-apps/coreutils-9
 	>=sys-devel/gcc-11
-	<sys-devel/gcc-16
 	>=sys-libs/ncurses-6
 	>=virtual/zlib-1.3.1:=
 	|| (
@@ -115,6 +141,8 @@ BDEPEND="
 		llvm-core/clang:${LLVM_SLOT}=
 		llvm-core/lld:${LLVM_SLOT}=
 	')
+	libcxx? ( $(llvm_gen_dep '=llvm-runtimes/libcxx-${LLVM_SLOT}*') )
+	!libcxx? ( $(_swift_llvm_gen_cond_dep '<sys-devel/gcc-16' {17..21}) )
 	dev-lang/python
 	$(python_gen_cond_dep 'dev-python/setuptools[${PYTHON_USEDEP}]')
 "
@@ -209,14 +237,16 @@ src_configure() {
 		fi
 	fi

-	if [[ "$(tc-get-cxx-stdlib)" = 'libc++' ]]; then
-		# On systems which use libc++ as their default C++ stdlib (e.g. systems
-		# with the LLVM profile), we want to build the internal libc++ and
-		# ensure we link against it.
+	if use libcxx; then
 		extra_build_flags+=(
 			--libcxx
 			--extra-cmake-options=-DCLANG_DEFAULT_CXX_STDLIB=libc++
 		)
+	elif [[ "${LLVM_SLOT}" -ge 22 ]]; then
+		# While `__COUNTER__` is being standardized, Clang 22 considers it a C2Y
+		# extension, and produces compilation errors by default. The semantics
+		# haven't changed, so these can be downgraded to warnings.
+		append-cxxflags '-Wno-error=c2y-extensions'
 	else
 		# Swift is going to be building against GCC's libstdc++ using Clang, and
 		# GCC 16 libstdc++ headers can only be parsed by Clang 22 and later.