Installation issue: `gcc@16 % gcc+mold ^mold@2.38` fails, so do attempts to constraint `mold`'s version

[yizeyi18]

Steps to reproduce the issue

No response

Error message

see rui314/mold#1545 . The error is spack-independent.

Information on your system

• Spack: 1.3.0.dev0 (spack/spack@e2e5041)
• Builtin repo: 3388718
• Python: 3.12.1
• Platform: linux-ubuntu26.04-zen3

Additional information

The build error is totally mold's fault, mold @:2.40 always fails building gcc@16.

The spack-side issue is, when trying to constraint spack to refuse such spec, none of below works:

requires("mold@2.41:", when="@16: %gcc+mold")
requires("mold@2.41:", when="@16: ^gcc+mold")
requires("mold@2.41:", when="@16: +mold")
requires("mold@2.41:", when="@16:")
requires("mold@2.41:", when="@16: %[virtuals=c,cxx] gcc+mold")
requires("%[virtuals=c,cxx] gcc+mold %mold@2.41:", when="@16: %[virtuals=c,cxx] gcc+mold")
requires("^[virtuals=c,cxx] gcc+mold %mold@2.41:", when="@16: %[virtuals=c,cxx] gcc+mold")
conflicts("mold@:2.40", when="@16: %gcc+mold")
conflicts("mold@:2.40", when="@16: ^gcc+mold")
conflicts("mold@:2.40", when="@16: %gcc+mold")
conflicts("%gcc+mold ^mold@:2.40", when="@16: %gcc+mold")
conflicts("^gcc+mold %mold@:2.40", when="@16: %gcc+mold")
conflicts("%[virtuals=c,cxx] gcc+mold %mold@:2.40", when="@16: %[virtuals=c,cxx] gcc+mold")

Some of them accepts gcc@16 % gcc+mold and concretized a spec using gcc+mold %mold@2.38; the rest always fails on gcc@16 + mold.

To constraint spec of a build dependency, how to write that？My attempts failed; it may need some spack maintainer's help. @michaelkuhn @alalazo

General information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have run spack maintainers <name-of-the-package> and @mentioned any maintainers
• I have uploaded the build log and environment files
• I have searched the issues of this repo and believe this is not a duplicate