Steps to reproduce

With a packages.yaml like:

packages:
  zlib:
    require: cflags="-g"

spack spec zlib fails. Claiming that the requirements cannot be satisfied.

Error message

...
spack.error.SpackError: concretization failed for the following reasons:

   1. Cannot satisfy the requirements in packages.yaml for package 'zlib'. You may want to delete them to proceed with concretization. To check where the requirements are defined run 'spack config blame packages'

Information on your system

• spack config blame packages shows no non-default config (other than the one I explicitly add in this report)

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