Block Iteration

block-iteration experiment reserves the expansion block

The block-iteration experiment has been added as the gate for iterating a dependency, unit, or stack block over a count or for_each, declared through a nested expansion block, along with an enabled attribute on unit and stack blocks.

In this release the flag is reserved only, and enabling it has no behavioral effect. Writing an expansion block without the experiment now reports an error naming the flag, rather than leaving the block to be silently discarded:

the unit "app" block in /path/to/terragrunt.stack.hcl uses an expansion block, which requires the 'block-iteration' experiment; enable it with --experiment block-iteration

Track progress and share feedback in #4504.