[SPARK-14102][CORE] Block reset command in SparkShell

[dongjoon-hyun]

What changes were proposed in this pull request?

Spark Shell provides an easy way to use Spark in Scala environment. This PR adds reset command to a blocked list, also cleaned up according to the Scala coding style.

scala> sc
res0: org.apache.spark.SparkContext = org.apache.spark.SparkContext@718fad24
scala> :reset
scala> sc
<console>:11: error: not found: value sc
       sc
       ^

If we blocks reset, Spark Shell works like the followings.

scala> :reset
reset: no such command.  Type :help for help.
scala> :re
re is ambiguous: did you mean :replay or :require?

How was this patch tested?

Manual. Run bin/spark-shell and type :reset.

[dongjoon-hyun]

In Jira, I chose Spark Shell as a component, but here CORE is the nearest one.

[srowen]

Oh I see, hm, this is not actually tricky to implement now. Well, it's not a crazy idea, anyone have opinions on blocking :reset? People really just shouldn't call it, and should restart the shell.

[dongjoon-hyun]

Thank you for review, @srowen .

[dongjoon-hyun]

Oh, I didn't search properly to find the duplicated JIRA issue: SPARK-6335.
Thank you for correcting me there.

[SparkQA]

Test build #53965 has finished for PR 11920 at commit 8b14dba.

• This patch fails from timeout after a configured wait of 250m.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #53995 has finished for PR 11920 at commit 7a438ae.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #54053 has finished for PR 11920 at commit d071621.

• This patch fails from timeout after a configured wait of 250m.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #54123 has finished for PR 11920 at commit 62a4020.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[dongjoon-hyun]

Hi, @srowen .
Recently Jenkins was a little bit flakey.
How do you think about this PR now?
The code is the same. It is just rebased to pass the test.

[srowen]

OK. If it's pretty simple and there is no good reason to call reset (since it kills the SparkContext) maybe it is worth blocking after all.

[dongjoon-hyun]

Thank you for the positive feedback. Indeed, it was just one-line change to block reset.
All the other changes in that file are just about ScalaStyle corrections.
Could you merge this PR, then?

[srowen]

Merged to master

[dongjoon-hyun]

Thank you, @srowen !