spack/etc/spack/defaults/concretizer.yaml

# -------------------------------------------------------------------------
# This is the default spack configuration file.
#
# Settings here are versioned with Spack and are intended to provide
# sensible defaults out of the box. Spack maintainers should edit this
# file to keep it current.
#
# Users can override these settings by editing
# `$SPACK_ROOT/etc/spack/concretizer.yaml`, `~/.spack/concretizer.yaml`,
# or by adding a `concretizer:` section to an environment.
# -------------------------------------------------------------------------
concretizer:
  # Whether to consider installed packages or packages from buildcaches when
  # concretizing specs. If `true`, we'll try to use as many installs/binaries
  # as possible, rather than building. If `false`, we'll always give you a fresh
  # concretization. If `dependencies`, we'll only reuse dependencies but
  # give you a fresh concretization for your root specs.
  reuse: dependencies
  # Options that tune which targets are considered for concretization. The
  # concretization process is very sensitive to the number targets, and the time
  # needed to reach a solution increases noticeably with the number of targets
  # considered.
  targets:
    # Determine whether we want to target specific or generic
    # microarchitectures. Valid values are: "microarchitectures" or "generic".
    # An example of "microarchitectures" would be "skylake" or "bulldozer",
    # while an example of "generic" would be "aarch64" or "x86_64_v4".
    granularity: microarchitectures
    # If "false" allow targets that are incompatible with the current host (for
    # instance concretize with target "icelake" while running on "haswell").
    # If "true" only allow targets that are compatible with the host.
    host_compatible: true
  # When "true" concretize root specs of environments together, so that each unique
  # package in an environment corresponds to one concrete spec. This ensures
  # environments can always be activated. When "false" perform concretization separately
  # on each root spec, allowing different versions and variants of the same package in
  # an environment.
  unify: true
  # Option to deal with possible duplicate nodes (i.e. different nodes from the same package) in the DAG.
  duplicates:
    # "none": allows a single node for any package in the DAG.
    # "minimal": allows the duplication of 'build-tools' nodes only (e.g. py-setuptools, cmake etc.)
    # "full" (experimental): allows separation of the entire build-tool stack (e.g. the entire "cmake" subDAG)
    strategy: minimal