Steps to reproduce

$ spack spec -lt ninja^[email protected]
Input spec
--------------------------------
[    ]  ninja
[    ]      ^[email protected]

Concretized
--------------------------------
jugtnbl  [    ]  [email protected]%[email protected] arch=linux-ubuntu20.04-x86_64_v3
cboatoj  [b   ]      ^[email protected]%[email protected]+bz2+ctypes+dbm~debug+ensurepip+libxml2+lzma~nis~optimizations+pic+pyexpat+pythoncmd+readline+shared+sqlite3+ssl~tix~tkinter~ucs4+uuid+zlib patches=0d98e93,4c24573,f2fd060 arch=linux-ubuntu20.04-x86_64_v3
[...]
$ 
--------------------------------
[    ]  ninja
[    ]      ^[email protected]

Concretized
--------------------------------
b4mlafv  [    ]  [email protected]%[email protected] arch=linux-ubuntu20.04-x86_64_v3
ndozxrc  [b   ]      ^[email protected]%[email protected]+bz2+ctypes+dbm~debug+ensurepip+libxml2+lzma~nis~optimizations+pic+pyexpat+pythoncmd+readline+shared+sqlite3+ssl~tix~tkinter~ucs4+uuid+zlib patches=0d98e93,4c24573,f2fd060 arch=linux-ubuntu20.04-x86_64_v3

[...]

Error message

According to the documentation (https://spack.readthedocs.io/en/latest/packaging_guide.html), the hash should not change if this is a build-only dependency:

Another consequence of this is that build-only dependencies do not affect the hash of the package.

However, the hash changes for every python version that I use here.
Perhaps the documentation is misleading me here or dependencies on python are somewhat special...

The documented behavior would be very helpful as the changing hashes of ninja lead to rebuilding lots of other dependencies...

Information on your system

• Spack: 0.18.1 (13e6f87)
• Python: 3.8.10
• Platform: linux-ubuntu20.04-skylake_avx512
• Concretizer: clingo

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