Bug#1086702: llvm-toolchain-19: FTBFS: Could not find wasi-libc on the system

[Duetsch, Thomas]

Source: llvm-toolchain-19
Version: 19.1.2-2
Tags: ftbfs

Dear Maintainer,

The source package llvm-toolchain-19 FTBFS on a current Trixie system running on ARM64.
Log output:
---
# llvm-spirv was found, so we can enable *.spv files. Debian
# buster and Ubuntu 18.04 don't have llvm-spirv to create the
# *.spv files.
if test "no" = "yes"; then \
	sed -i -e "s|#spv\ ||g" debian/libclc-19.install; \
fi
# disable libc++-X.Y-dev-wasm32.install.in on old distro
if test "yes" = "no"; then \
	echo "" > debian/libc++-19-dev-wasm32.install; \
	echo "" > debian/libc++abi-19-dev-wasm32.install; \
else \
	if ! dpkg -l|grep -q wasi-libc; then \
		echo "Could not find wasi-libc on the system"; \
		echo "Please check that the package is available on the system"; \
		echo "it might be that the 'hello' package is installed by another constraint"; \
		exit 1; \
	fi; \
fi
Could not find wasi-libc on the system
Please check that the package is available on the system
it might be that the 'hello' package is installed by another constraint
make[1]: *** [debian/rules:699: stamps/preconfigure] Error 1
make[1]: Leaving directory '/work/tmp/llvm-toolchain-19_19.1.2-2/llvm-toolchain-19-19.1.2'
make: *** [debian/rules:646: binary] Error 2
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2
debuild: fatal error at line 1184:
dpkg-buildpackage -us -uc -ui -j6 -F failed
---

Digging into the control file, we found this patch:
https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/commit/b13a5e5005bcc0da6bde1a2331d82c14e79fd9d1

This seems to break the build-dependencies for an ARM based build. The patch ignores the warning described a few lines below regarding the constraints of the alternatives.
Below is a small patch which fixes the issue for us.

---
diff -ru debian/control debian.new/control
--- debian/control      2024-10-26 07:14:42.000000000 +0000
+++ debian.new/control  2024-11-04 11:43:58.460681442 +0000
@@ -16,7 +16,7 @@
     libipt-dev [amd64 i386],
     lcov, procps, help2man,
     zlib1g-dev, libzstd-dev,
-    g++-multilib [amd64 i386 mips64 mips64el mipsel powerpc ppc64 s390x sparc sparc64 x32] | hello,
+    g++-multilib [amd64 i386 mips64 mips64el mipsel powerpc ppc64 s390x sparc sparc64 x32] | hello [amd64 i386 mips64 mips64el mipsel powerpc ppc64 s390x sparc sparc64 x32],
     libjs-mathjax, python3-myst-parser | python3-recommonmark, python3-pexpect,
     doxygen, time,
     ocaml-base [amd64 arm64 ppc64el riscv64 s390x] | ocaml-nox [amd64 arm64 ppc64el riscv64 s390x],
diff -ru debian/control.in debian.new/control.in
--- debian/control.in   2024-10-26 07:14:42.000000000 +0000
+++ debian.new/control.in       2024-11-04 11:44:15.650681247 +0000
@@ -16,7 +16,7 @@
     libipt-dev [amd64 i386],
     lcov, procps, help2man,
     zlib1g-dev, libzstd-dev,
-    g++-multilib [@MULTILIB_ARCHS@] | hello,
+    g++-multilib [@MULTILIB_ARCHS@] | hello [@MULTILIB_ARCHS@],
     libjs-mathjax, python3-myst-parser | python3-recommonmark, python3-pexpect,
     doxygen, at USAGE_BUILD_DEP@
     ocaml-base [@OCAML_ARCHS@] | ocaml-nox [@OCAML_ARCHS@],---

With best regards,
Thomas Duetsch