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[SPARK-3873][BUILD] Add style checker to enforce import ordering.
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The checker tries to follow as closely as possible the guidelines of
the code style document, and makes some decisions where the guide is
not clear. In particular:

- wildcard imports come first when there are other imports in the
  same package
- multi-import blocks come before single imports
- lower-case names inside multi-import blocks come before others

In some projects, such as graphx, there seems to be a convention to
separate o.a.s imports from the project's own; to simplify the
checker, I chose not to allow that, which is a strict interpretation
of the code style guide, even though I think it makes sense.

Since the checks are based on syntax only, some edge cases may
generate spurious warnings; for example, when class names start
with a lower case letter (and are thus treated as a package name
by the checker).

The checker is currently only generating warnings, and since there
are many of those, the build output does get a little noisy. The
idea is to fix the code (and the checker, as needed) little by little
instead of having a huge change that touches everywhere.

Author: Marcelo Vanzin <[email protected]>

Closes apache#6502 from vanzin/SPARK-3873.
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Marcelo Vanzin committed Dec 8, 2015
1 parent 06746b3 commit 2ff17bc
Showing 1 changed file with 13 additions and 1 deletion.
14 changes: 13 additions & 1 deletion scalastyle-config.xml
Original file line number Diff line number Diff line change
Expand Up @@ -153,7 +153,7 @@ This file is divided into 3 sections:
<check customId="visiblefortesting" level="error" class="org.scalastyle.file.RegexChecker" enabled="true">
<parameters><parameter name="regex">@VisibleForTesting</parameter></parameters>
<customMessage><![CDATA[
@VisibleForTesting auses classpath issues. Please note this in the java doc instead (SPARK-11615).
@VisibleForTesting causes classpath issues. Please note this in the java doc instead (SPARK-11615).
]]></customMessage>
</check>

Expand Down Expand Up @@ -203,6 +203,18 @@ This file is divided into 3 sections:
<!-- Should turn this on, but we have a few places that need to be fixed first -->
<check level="error" class="org.scalastyle.scalariform.EqualsHashCodeChecker" enabled="false"></check>

<!-- Import ordering. Currently warning only since there are lots of violations. -->
<check level="warning" class="org.scalastyle.scalariform.ImportOrderChecker" enabled="true">
<parameters>
<parameter name="groups">java,scala,3rdParty,spark</parameter>
<parameter name="group.java">javax?\..+</parameter>
<parameter name="group.scala">scala\..+</parameter>
<parameter name="group.3rdParty">(?!org\.apache\.spark\.).*</parameter>
<parameter name="group.spark">org\.apache\.spark\..*</parameter>
</parameters>
</check>


<!-- ================================================================================ -->
<!-- rules we don't want -->
<!-- ================================================================================ -->
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