Urm… I think

--exclude-target-regexp

does a little more than I want it to… I think it prevents those BUILD files from being parsed, whether as roots or deps, which means that any target which depends on an excluded target fails to parse:

Exception message: Build graph construction failed: ExecutionError Received unexpected Throw state(s):

...

Computing Select(SingleAddress(directory='testprojects/src/antlr/python/test', name='eval'), =Collection.of(HydratedTarget))
  Computing Task(<function transitive_hydrated_targets at 0x103864d70>, SingleAddress(directory='testprojects/src/antlr/python/test', name='eval'), =Collection.of(HydratedTarget))
    Computing Task(<function addresses_from_address_families at 0x10341ca28>, SingleAddress(directory='testprojects/src/antlr/python/test', name='eval'), =BuildFileAddresses)
      Throw("eval" was not found in namespace "testprojects/src/antlr/python/test". Did you mean one of:
  :antlr_failure
  :eval)
        Traceback (most recent call last):
          File "/Users/dwagnerhall/src/github.com/pantsbuild/pants/src/python/pants/engine/native.py", line 412, in extern_invoke_runnable
            val = runnable(*args)
          File "/Users/dwagnerhall/src/github.com/pantsbuild/pants/src/python/pants/engine/build_files.py", line 266, in addresses_from_address_families
            _raise_did_you_mean(address_families[0], spec.name)
          File "/Users/dwagnerhall/src/github.com/pantsbuild/pants/src/python/pants/engine/build_files.py", line 113, in _raise_did_you_mean
            .format(name, address_family.namespace, possibilities))
        ResolveError: "eval" was not found in namespace "testprojects/src/antlr/python/test". Did you mean one of:
          :antlr_failure
          :eval