What is the purpose of PrimordialHandler class and while default indent level is set to zero?

[kalpadiptyaroy]

I am raising this question due to #14149 (comment)

consider the code below.

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/PrimordialHandler.java

Lines 47 to 50 in 0723bc1

	@Override
	protected IndentLevel getIndentImpl() {
	return new IndentLevel(0);
	}

I wanted to enquire - what is purpose of hardcoding 0 as the default indent level?
And also, I want to understand the purpose of this class PrimordialHandler ?

[romani]

Try to go to git history to get links to issues and PRs when it was introduced.

[nrmancuso]

I would assume that the name PrimordialHandler is to hint that this is the base/initial/fundamental indentation handler; therefore we would always want the base indentation to be zero.

[rnveach]

The class literally says it is a no-op class. This means no indentation increase for whatever it points out.

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/PrimordialHandler.java

Line 23 in a4411aa

* A default no-op handler.

[kalpadiptyaroy]

Fine. I understood the purpose.
Now, I would like to ask whether the following behavior is the desired behavior or is it not?

When indentation check is triggered - then the program flows in the following way --

1. checkModifiers method is called.

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/AbstractExpressionHandler.java

Lines 496 to 508 in a4411aa

	protected void checkModifiers() {
	final DetailAST modifiers =
	mainAst.findFirstToken(TokenTypes.MODIFIERS);
	for (DetailAST modifier = modifiers.getFirstChild();
	modifier != null;
	modifier = modifier.getNextSibling()) {
	if (isOnStartOfLine(modifier)
	&& !getIndent().isAcceptable(expandedTabsColumnNo(modifier))) {
	logError(modifier, "modifier",
	expandedTabsColumnNo(modifier));
	}
	}
	}

2. getIndent method is called.

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/AbstractExpressionHandler.java

Lines 83 to 88 in a4411aa

	public final IndentLevel getIndent() {
	if (indent == null) {
	indent = getIndentImpl();
	}
	return indent;
	}

3. getIndentImpl method is called.

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/AbstractExpressionHandler.java

Lines 95 to 97 in a4411aa

	protected IndentLevel getIndentImpl() {
	return parent.getSuggestedChildIndent(this);
	}

Now, here this return parent.getSuggestedChildIndent(this); is has an overridden implementation and it executes the following method from PrimordialHandler for all the handlers that are executed by TreeWalker.

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/PrimordialHandler.java

Lines 48 to 50 in a4411aa

	protected IndentLevel getIndentImpl() {
	return new IndentLevel(0);
	}

Now, the question is: should it be like this:
that the IndentLevel's value is initially set to zero obeying the implementation of primordial handler, but when we are using another handler (e.g. ClassDefHandler .... etc) then, the indentlevel parameters' value should be overridden as per the configuration of that handler?

--------------------- UPDATE --------------------->>

I have further investigated and found the PrimordialHandler is injected as the parent of each handlers, here in IndentationCheck.

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/IndentationCheck.java

Lines 426 to 430 in a4411aa

	public void visitToken(DetailAST ast) {
	final AbstractExpressionHandler handler = handlerFactory.getHandler(this, ast,
	handlers.peek());
	handlers.push(handler);
	handler.checkIndentation();

[nrmancuso]

behavior

Figuring out how the code here is supposed to behave is a fool's errand, IMO. This is our most complicated (and buggy) check. It is better to focus on actual behavior, what we need to do to get to the expected check behavior, and thorough regression testing.

[kalpadiptyaroy]

may be you are right - but I have made certain fixes - explore here #14149 (comment)