GitHub user okram opened a pull request:
https://github.com/apache/tinkerpop/pull/527
TINKERPOP-1521: Mutating steps don't recognize side-effects
https://issues.apache.org/jira/browse/TINKERPOP-1521
`AddVertexStartStep` was using an `EmptyTraverser` to compute the
`Parameters`. I thus, create a dummy traverser that has respective traversal
side-effects. Added two new test cases to `AddVertexTest`.
```groovy
gremlin> g = TinkerGraph.open().traversal()
==>graphtraversalsource[tinkergraph[vertices:0 edges:0], standard]
gremlin> g.withSideEffect("a", "marko").addV().property("name", select("a"))
==>v[0]
gremlin> g.V().valueMap()
==>[name:[marko]]
gremlin>
```
Finally, realized that `PathRetractionStrategy` was adding a
`NoOpBarrierStep` to the end of local traversal. This is pointless computation
as 99% of local traversals are `by()`-modulators that only need the first
`next()`.
VOTE +1.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/apache/tinkerpop TINKERPOP-1521
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/tinkerpop/pull/527.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #527
----
commit 276064530617c04706b62ac57ec4e2e660a756a4
Author: Marko A. Rodriguez <okramma...@gmail.com>
Date: 2017-01-09T16:36:15Z
fixed an NPE in AddVertexStartStep. In PathRetractionStrategy, NoOpBarriers
are only added to global children as 99% of local children are by()-modulation
based and thus, there is no point to fully compute the traversal if only the
first next() is going to be used.
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