From 282749749da38aa746e403ce8f2cf1ed50f49845 Mon Sep 17 00:00:00 2001
From: Michal Rostecki <vadorovsky@protonmail.com>
Date: Tue, 11 Nov 2025 14:19:40 +0100
Subject: [PATCH] dev-lang/rust: Require clang when building WASM sysroot
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GCC does not support WASM. Require clang to build C code for WASM
target and make sure it's actually used.

[mgorny: added strip-unsupported-flags too]

Bug: https://bugs.gentoo.org/965346
Signed-off-by: Michal Rostecki <vadorovsky@protonmail.com>
Part-of: https://github.com/gentoo/gentoo/pull/44594
Closes: https://github.com/gentoo/gentoo/pull/44594
Signed-off-by: Michał Górny <mgorny@gentoo.org>
---
 dev-lang/rust/rust-1.92.0_p1-r1.ebuild | 17 ++++++++++++++++-
 dev-lang/rust/rust-9999.ebuild         | 17 ++++++++++++++++-
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/dev-lang/rust/rust-1.92.0_p1-r1.ebuild b/dev-lang/rust/rust-1.92.0_p1-r1.ebuild
index f5073db6688b3..6086b58e2f2fa 100644
--- a/dev-lang/rust/rust-1.92.0_p1-r1.ebuild
+++ b/dev-lang/rust/rust-1.92.0_p1-r1.ebuild
@@ -125,6 +125,7 @@ BDEPEND="
 			sys-devel/mold
 		)
 	) )
+	rust_sysroots_wasm? ( llvm-core/clang )
 	!system-llvm? (
 		>=dev-build/cmake-3.13.4
 		app-alternatives/ninja
@@ -587,9 +588,23 @@ src_configure() {
 	done
 	if use rust_sysroots_wasm; then
 		wasm_target="wasm32-unknown-unknown"
-		export CFLAGS_${wasm_target//-/_}="$(filter-flags '-mcpu*' '-march*' '-mtune*'; echo "$CFLAGS")"
+		if tc-is-clang; then
+			local wasm_cc=$(tc-getCC)
+			local wasm_cxx=$(tc-getCXX)
+		else
+			local wasm_cc=${CHOST}-clang
+			local wasm_cxx=${CHOST}-clang++
+		fi
+		export CFLAGS_${wasm_target//-/_}="$(
+			CC="${wasm_cc} --target=wasm32-unknown-unknown"
+			filter-flags '-mcpu*' '-march*' '-mtune*'
+			strip-unsupported-flags
+			echo "${CFLAGS}"
+		)"
 		cat <<- _EOF_ >> "${S}"/bootstrap.toml
 			[target.wasm32-unknown-unknown]
+			cc = "${wasm_cc}"
+			cxx = "${wasm_cxx}"
 			linker = "$(usex system-llvm lld rust-lld)"
 			# wasm target does not have profiler_builtins https://bugs.gentoo.org/848483
 			profiler = false
diff --git a/dev-lang/rust/rust-9999.ebuild b/dev-lang/rust/rust-9999.ebuild
index f5073db6688b3..6086b58e2f2fa 100644
--- a/dev-lang/rust/rust-9999.ebuild
+++ b/dev-lang/rust/rust-9999.ebuild
@@ -125,6 +125,7 @@ BDEPEND="
 			sys-devel/mold
 		)
 	) )
+	rust_sysroots_wasm? ( llvm-core/clang )
 	!system-llvm? (
 		>=dev-build/cmake-3.13.4
 		app-alternatives/ninja
@@ -587,9 +588,23 @@ src_configure() {
 	done
 	if use rust_sysroots_wasm; then
 		wasm_target="wasm32-unknown-unknown"
-		export CFLAGS_${wasm_target//-/_}="$(filter-flags '-mcpu*' '-march*' '-mtune*'; echo "$CFLAGS")"
+		if tc-is-clang; then
+			local wasm_cc=$(tc-getCC)
+			local wasm_cxx=$(tc-getCXX)
+		else
+			local wasm_cc=${CHOST}-clang
+			local wasm_cxx=${CHOST}-clang++
+		fi
+		export CFLAGS_${wasm_target//-/_}="$(
+			CC="${wasm_cc} --target=wasm32-unknown-unknown"
+			filter-flags '-mcpu*' '-march*' '-mtune*'
+			strip-unsupported-flags
+			echo "${CFLAGS}"
+		)"
 		cat <<- _EOF_ >> "${S}"/bootstrap.toml
 			[target.wasm32-unknown-unknown]
+			cc = "${wasm_cc}"
+			cxx = "${wasm_cxx}"
 			linker = "$(usex system-llvm lld rust-lld)"
 			# wasm target does not have profiler_builtins https://bugs.gentoo.org/848483
 			profiler = false