Steps to reproduce

I have a minimal reproducing Spack package called foo:

from spack_repo.builtin.build_systems.cmake import CMakePackage
from spack.package import *


class Foo(CMakePackage):
    git = "https://github.com/mycpptutorial/helloworld-cmake"

    depends_on("c", type="build")
    depends_on("cxx", type="build")

    version("develop", branch="master")

    depends_on("llvm@18:")

The package is in a repository that I have registered (using spack repo add) and spack info foo suceeds.

Error message

Trying to concretize a simple spec using the package and specifying LLVM as the compiler results in an internal solver error:

$ spack spec foo %c,cxx=llvm
==> Error: internal solver error: the following specs were concretized, but do not satisfy the input:
    - input: foo %c,cxx=clang
      output: <...>
    Please report a bug at https://github.com/spack/spack/issues and attach the following files:
    - /tmp/spack-asp-tupb8lee/input-1.json
    - /tmp/spack-asp-tupb8lee/output-1.json

input-1.json
output-1.json

(Censored) output of spack --debug --stacktrace spec foo %c,cxx=llvm: spack-stacktrace.log

Interestingly, the problem does not occur when I remove the depends_on("llvm@18:") from the package.

Information on your system

• Spack: 1.1.0.dev0 (9a0e926)
• Builtin repo: spack/spack-packages@668dce2
• Python: 3.9.18
• Platform: linux-rhel9-cascadelake

$ spack compiler list
==> Available compilers
-- gcc rhel9-x86_64 ---------------------------------------------
[e]  gcc@11.4.1

-- llvm rhel9-x86_64 --------------------------------------------
[+]  llvm@main  [+]  llvm@18.1.8

General information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have searched the issues of this repo and believe this is not a duplicate
• I have run the failing commands in debug mode and reported the output