tree 62fa81d09202079aa196d46db09c932a5ce30a63
parent 027e9b21e6605fb1f954636d39681aa4d678b189
author Chenchu Kolli <ckolli@google.com> 1652142874 -0500
committer Yun Peng <pcloudy@google.com> 1652190803 +0200

Unify sandbox/remote handling of empty TreeArtifact inputs (#15449)

Actions that take a TreeArtifact as input should see a corresponding
directory even if the TreeArtifact is empty.

Previously, SandboxHelpers contained special handling for the case of
empty TreeArtifact action inputs to ensure that they are added to the
sandbox as empty directories. As pointed out in a comment, this logic
should live in SpawnInputExpander, where it would also apply to remote
execution.

This commit adds a integration tests for this previously untested case,
extracts the logic into SpawnInputExpander and adapts
DirectoryTreeBuilder to handle empty TreeArtifacts when creating the
Merkle trees.

Note: The Merkle tree builder now reports an error when it encounters a
non-empty TreeArtifact. Such an artifact should have been expanded by
SpawnInputExpander and if it wasn't, e.g. because it wasn't properly
registered with Skyframe, it can't be expanded at this point anyway.
The tests uncovered that the spawn for split coverage postprocessing declared the
coverage dir artifact as such an input. In this case, it can simply be
removed as the coverage script creates the coverage dir if it doesn't
exist.

Closes #15276.

PiperOrigin-RevId: 446452587

Co-authored-by: Fabian Meumertzheim <fabian@meumertzhe.im>