gitlab ci: Provide a knob to control untouched spec pruning (#35274)

When untouched spec pruning is enabled, specs possibly affected
by a change cannot be pruned from a pipeline.

Previously spack looked at all specs matching changed package
names, and traversed dependents of each, all the way to the
environment root, to compute the set of environment specs
possibly affected by a change (and thus, not candidates for
pruning).

With this PR, when untouched spec pruning is enabled, a new
environment variable can control how far towards the root spack
traverses to compute the set of specs possibly affected by a
change.  SPACK_UNTOUCHED_PRUNING_DEPENDENT_DEPTH can be set
to any numeric value before the "spack ci generate" command
is called to control this traversal depth parameter.  Setting
it to "0" traverses only touched specs, setting it to "1"
traverses only touched specs and their direct dependents, and
so on.  Omitting the variable results in the previous behavior
of traversing all the way to the root.  Setting it to a negative
value means no traversal is done, and always yields an empty
set of possibly affected specs (which would result in the max
pruning possible).

0 files changed, 0 insertions, 0 deletions