EmptyLineSeparator: Inability to use xpath for violation on empty line

[shashwatj07]

Split from #7956

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/whitespace/EmptyLineSeparatorCheck.java

Line 419 in a8a90cf

log(lineNo + 1, MSG_MULTIPLE_LINES_INSIDE);

There is no AST node associated an empty line for which the violations are logged. This results the inability of such violations to be xpath suppressed. We may need to change the violation a bit to make it compliant with xpath.

C:\Users\Shashwat\Documents>cat config.xml
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
          "https://checkstyle.org/dtds/configuration_1_3.dtd">
<module name="Checker">
  <module name="TreeWalker">
        <module name="EmptyLineSeparator">
        <property name="allowMultipleEmptyLinesInsideClassMembers" value="false"/>
        <property name="allowMultipleEmptyLines" value="false"/>
        </module>
  </module>
</module>
C:\Users\Shashwat\Documents>cat Test.java
class A {



    void foo() { // line 5



    } // line 9
}
C:\Users\Shashwat\Documents>java -jar checkstyle-8.31-all.jar -c config.xml Test.java
Starting audit...
[ERROR] C:\Users\Shashwat\Documents\Test.java:5: 'METHOD_DEF' has more than 1 empty lines before. [EmptyLineSeparator]
[ERROR] C:\Users\Shashwat\Documents\Test.java:7: There is more than 1 empty line one after another. [EmptyLineSeparator]
[ERROR] C:\Users\Shashwat\Documents\Test.java:8: There is more than 1 empty line one after another. [EmptyLineSeparator]
Audit done.
Checkstyle ends with 3 errors.

In the above example it is clear that when we have to log violation for a similar case, outside the class members, we do it in a single go.
Test.java:5: 'METHOD_DEF' has more than 1 empty lines before. [EmptyLineSeparator]
This can be extended to solve this issue as well, where instead of logging for every empty line, we can log violation for the above example as follows:
Test.java:9: There is more than 1 empty line above. [EmptyLineSeparator]
However, the node to be logged is a bit uncertain. This needs to be dicussed.

[romani]

it is not critical on what node to print violation as in java you always have some character after - end of class scope. It would be good to report on previous token always, as we always know it existed and we do NOT know what will be on next line, this will be more reliable approach I think.

[HuGanghui]

@romani it' ok to move violation report on previous token, right? If yes, I will plan to solve this issue.

[romani]

it' ok to move violation report on previous token, right?

Right. You are welcome to send PR

[AkMo3]

I am on it.

[romani]

merged

[cowwoc]

Shouldn't the warning be removed from the documentation? https://checkstyle.org/checks/whitespace/emptylineseparator.html#EmptyLineSeparator

[romani]

@cowwoc , thanks a lot for heads up #13506