/**
* Creates a middleman for the compilation prerequisites.
*
* @return the middleman or null if there are no prerequisites
*/
private Artifact createMiddleman(ActionOwner owner, MiddlemanFactory middlemanFactory) {
if (compilationPrerequisites.isEmpty()) {
return null;
}
// Compilation prerequisites gathered in the compilationPrerequisites
// must be generated prior to executing C++ compilation step that depends
// on them (since these prerequisites include all potential header files, etc
// that could be referenced during compilation). So there is a definite need
// to ensure scheduling edge dependency. However, those prerequisites should
// have no effect on the decision whether C++ compilation should happen in
// the first place - only CppCompileAction outputs (*.o and *.d files) and
// all files referenced by the *.d file should be used to make that decision.
// If this action was never executed, then *.d file would be missing, forcing
// compilation to occur. If *.d file is present and has not changed then the
// only reason that would force us to re-compile would be change in one of
// the files referenced by the *.d file, since no other files participated
// in the compilation. We also need to propagate errors through this
// dependency link. So we use an error propagating middleman.
// Such middleman will be ignored by the dependency checker yet will still
// represent an edge in the action dependency graph - forcing proper execution
// order and error propagation.
return middlemanFactory.createErrorPropagatingMiddleman(
owner,
ruleContext.getLabel().toString(),
purpose,
ImmutableList.copyOf(compilationPrerequisites),
ruleContext
.getConfiguration()
.getMiddlemanDirectory(ruleContext.getRule().getRepository()));
}
/**
* Returns the same set of artifacts as createMiddleman() would, but without actually creating
* middlemen.
*/
private Artifact getMiddlemanArtifact(MiddlemanFactory middlemanFactory) {
if (compilationPrerequisites.isEmpty()) {
return null;
}
return middlemanFactory.getErrorPropagatingMiddlemanArtifact(
ruleContext.getLabel().toString(),
purpose,
ruleContext
.getConfiguration()
.getMiddlemanDirectory(ruleContext.getRule().getRepository()));
}