cross/crossdirect: support rust

Install two new wrappers to speed up cross compiling rust packages, by
using the native cross compiler.

Related: pmbootstrap#1861

cross/crossdirect/APKBUILD

@@ -5,21 +5,24 @@
 #
 # /native/usr/lib/crossdirect/armhf/gcc
 # -> /native/usr/bin/armv6-alpine-linux-muslgnueabihf-gcc
+# /native/usr/lib/crossdirect/armhf/rustc
+# -> /native/usr/bin/rustc --target=armv6-alpine-linux-musleabihf ...
 #
 # When building packages in the armhf chroot, PATH will get prepended with
 # "/native/usr/lib/crossdirect/armhf". The end game is of course invoking the
 # cross compiler from the native chroot, running at native speed, whenever
 # calling the compiler from the foreign arch chroot. See crossdirect.c for
-# implementation details (llvm, fakeroot, rpath).
+# implementation details of the C version (llvm, fakeroot, rpath). The rust
+# version is implemented as simple shell wrappers below.
 
 pkgname=crossdirect
-pkgver=3
-pkgrel=1
+pkgver=4
+pkgrel=0
 pkgdesc="Wrappers to launch native cross compilers in foreign chroots"
 url="https://postmarketOS.org"
 arch="all"
 license="MIT"
-options=""
+options="!check"
 source="crossdirect.c"
 
 build() {
@@ -40,27 +43,71 @@ build() {
 	done
 }
 
+rust_triplet() {
+	# Find the triplets in Alpine's rust APKBUILD or with:
+	# pmbootstrap chroot -barmhf --add=rust -- ls /usr/lib/rustlib
+	case "$1" in
+		x86_64)
+			echo "x86_64-alpine-linux-musl"
+			;;
+		armhf)
+			echo "arm-unknown-linux-musleabihf"
+			;;
+		armv7)
+			echo "armv7-unknown-linux-musleabihf"
+			;;
+		aarch64)
+			echo "aarch64-unknown-linux-musl"
+			;;
+		*)
+			echo "ERROR: don't know the rust triple for $1!" >&2
+			exit 1
+			;;
+	esac
+}
+
 package() {
 	# Architectures and binaries
 	_archs="x86_64 armhf armv7 aarch64"
 	_bins="c++ cc cpp g++ gcc clang clang++"
 
+	# Rust: crossdirect-clinker
+	# Invoked from native rustc, resets LD_LIBRARY_PATH and runs foreign
+	# arch GCC for linking
+	_clinker="$pkgdir/usr/lib/crossdirect/clinker"
+	mkdir -p "$pkgdir/usr/lib/crossdirect"
+	( echo "#!/bin/sh"
+	  echo "LD_LIBRARY_PATH=/lib:/usr/lib \\"
+	  echo '  gcc "$@"' ) > "$_clinker"
+	chmod +x "$_clinker"
+
 	# Iterate over architectures
 	for _arch in $_archs; do
 		[ "$_arch" == "$CARCH" ] && continue
 
-		# Put arch-specific crossdirect wrapper in arch-specific bin folder
+		# GCC: put arch-specific crossdirect wrapper in arch-specific
+		# bin folder
 		_bindir="$pkgdir/usr/lib/crossdirect/$_arch"
 		_hostspec="$(arch_to_hostspec $_arch)"
 		mkdir -p "$_bindir"
 		cd "$_bindir"
 		cp "$srcdir/crossdirect-$_arch" "./"
 
-		# Create compiler symlinks
+		# GCC: create compiler symlinks
 		for _bin in $_bins; do
 			ln -s "crossdirect-$_arch" "$_bin"
 			ln -s "crossdirect-$_arch" "$_hostspec-$_bin"
 		done
+
+		# Rust: arch-specific rustc wrapper
+		( echo "#!/bin/sh"
+		  echo "LD_LIBRARY_PATH=/native/lib:/native/usr/lib \\"
+		  echo "  /native/usr/bin/rustc \\"
+		  echo "    -Clinker=/native/usr/lib/crossdirect/clinker \\"
+		  echo "    --target=$(rust_triplet "$_arch") \\"
+		  echo "    --sysroot=/usr \\"
+		  echo '    "$@"' ) > "$_bindir/rustc"
+		chmod +x "$_bindir/rustc"
 	done
 }
 sha512sums="20b963322820de038257304c1eefa85767b78e242eda7459f06d70a1cfae5540a445aa7d5587024bf4d88a4bee28120ef9f5c2d24a648e71b542b9618318deb2  crossdirect.c"