Fix #5590: [java] LiteralsFirstInComparisons with constant field

[oowekyala]

Describe the PR

To fix this i had to refactor a bit the constant folding logic. It wasn't actually implementing the definition of the JLS for a "compile-time constant". The logic now makes ASTExpression#isCompileTimeConstant() and #getConstValue() respect the JLS definition, that is, the only variables referenced must be compile-time constant fields (ie static final with CT constant initializer, and cannot have blank initializer). However this is very restrictive, while some rules want to know if the value is known at compile time, even if it uses non-static final fields, or final local variables for instance. I extended the logic of the constant folder to track whether the resolved constant value is a CT constant according to the strict definition or to the loose definition.

Related issues

• Fix [java] LiteralsFirstInComparisonsRule not applied on constant #5590

Ready?

• Added unit tests for fixed bug/feature
• Passing all unit tests
• Complete build ./mvnw clean verify passes (checked automatically by github actions)
• Added (in-code) documentation (if needed)

[github-actions]

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Compared to main:
This changeset changes 0 violations,
introduces 31 new violations, 0 new errors and 0 new configuration errors,
removes 11 violations, 0 errors and 0 configuration errors.

Regression Tester Report

[adangel]

Thanks!

[adangel]

isCompileTimeConstant can also be removed here and the default from ASTExpression can be used.

[adangel]

Ok, this change broke the (treedump) tests, that expect that NullLiterals are not compile-time constants. See also

pmd/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/AbstractLiteral.java

Lines 58 to 60 in 120c2bb

	public boolean isCompileTimeConstant() {
	return true; // note: NullLiteral overrides this to false
	}

@oowekyala I would have expected, that all literals are compile time constants. But this doesn't seem to be the case for null? Is this correct? Do you know, why?
If I understand it correctly, compile-time constants can only be created by Constant Expressions which is of a primitive type or String. But null is neither, therefore null is not a compile-time constant...