add baseline functionality for not saving unused artifacts

We define unused artifacts as those that aren't consumed by any
action. This can be because an action produced more outputs than
a dependent action needed, or because it's a top level artifact
and we don't care about its contents, just that it was built
without issue. Actions may prevent outputs from being discarded
by declaring them as mandatory. This is particularly useful for
test outputs. The motivation behind this change is to reduce
storage overhead for things we can do without.

It is worth noting this change doesn't cover all cases. In particular
it has difficulty identifying *_binary artifacts as orphaned. This
is due to the insertion of a virtual runfiles artifact which depends
upon the rule's outputs.

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MOS_MIGRATED_REVID=88467504

1 files changed, 8 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/actions/ActionMetadata.java b/src/main/java/com/google/devtools/build/lib/actions/ActionMetadata.java
index 3569f07a8b..64813aed07 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/ActionMetadata.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/ActionMetadata.java
@@ -124,6 +124,14 @@ public interface ActionMetadata {
   ImmutableSet<Artifact> getOutputs();
 
   /**
+   * Returns the set of output Artifacts that are required to be saved. This is
+   * used to identify items that would otherwise be potentially identified as
+   * orphaned (not consumed by any downstream {@link Action}s and potentially
+   * discarded during the build process.
+   */
+  public ImmutableSet<Artifact> getMandatoryOutputs();
+
+  /**
    * Returns the "primary" input of this action, if applicable.
    *
    * <p>For example, a C++ compile action would return the .cc file which is being compiled,