Add filter for Kotlin enum classes

[Godin]

Fixes #1557

[leveretka]

Overall looks good, thanks for fixing it!

I just have a small suggestion to improve readability.

[leveretka]

I don't know if this is the convention here, but as a code reader, I'd prefer to see a single if without negations in the conditions to reduce a cognitive load. Since the body of the if is just one line, this is an acceptable level of nesting.

[Godin]

We don't have a strict convention about this and both styles can be found, but seems that the early-returns style is prevalent:

single if in

jacoco/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/EnumEmptyConstructorFilter.java

Lines 39 to 48 in 5aabb2e

	public void filter(final MethodNode methodNode,
	final IFilterContext context, final IFilterOutput output) {
	if (ENUM_TYPE.equals(context.getSuperClassName())
	&& CONSTRUCTOR_NAME.equals(methodNode.name)
	&& CONSTRUCTOR_DESC.equals(methodNode.desc)
	&& new Matcher().match(methodNode)) {
	output.ignore(methodNode.instructions.getFirst(),
	methodNode.instructions.getLast());
	}
	}

jacoco/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/PrivateEmptyNoArgConstructorFilter.java

Lines 26 to 35 in 5aabb2e

	public void filter(final MethodNode methodNode,
	final IFilterContext context, final IFilterOutput output) {
	if ((methodNode.access & Opcodes.ACC_PRIVATE) != 0
	&& CONSTRUCTOR_NAME.equals(methodNode.name)
	&& CONSTRUCTOR_DESC.equals(methodNode.desc) && new Matcher()
	.match(methodNode, context.getSuperClassName())) {
	output.ignore(methodNode.instructions.getFirst(),
	methodNode.instructions.getLast());
	}
	}

early returns in

jacoco/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/BridgeFilter.java

Lines 23 to 30 in 5aabb2e

	public void filter(final MethodNode methodNode,
	final IFilterContext context, final IFilterOutput output) {
	if ((methodNode.access & Opcodes.ACC_BRIDGE) == 0) {
	return;
	}
	output.ignore(methodNode.instructions.getFirst(),
	methodNode.instructions.getLast());
	}

jacoco/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/KotlinInlineClassFilter.java

Lines 74 to 87 in 5aabb2e

	public void filter(final MethodNode methodNode,
	final IFilterContext context, final IFilterOutput output) {
	if (!KotlinGeneratedFilter.isKotlinClass(context)) {
	return;
	}
	if (!context.getClassAnnotations().contains("Lkotlin/jvm/JvmInline;")) {
	return;
	}
	if ((methodNode.access & Opcodes.ACC_STATIC) != 0) {
	return;
	}
	output.ignore(methodNode.instructions.getFirst(),
	methodNode.instructions.getLast());
	}

jacoco/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/KotlinGeneratedFilter.java

Lines 31 to 50 in 5aabb2e

	public void filter(final MethodNode methodNode,
	final IFilterContext context, final IFilterOutput output) {
	if (context.getSourceFileName() == null) {
	// probably full debug information is missing
	// disabled filtering as all methods might be erroneously skipped
	return;
	}
	if (!isKotlinClass(context)) {
	return;
	}
	if (hasLineNumber(methodNode)) {
	return;
	}
	output.ignore(methodNode.instructions.getFirst(),
	methodNode.instructions.getLast());
	}

jacoco/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/KotlinDefaultMethodsFilter.java

Lines 25 to 31 in 5aabb2e

	public void filter(final MethodNode methodNode,
	final IFilterContext context, final IFilterOutput output) {
	if (!KotlinGeneratedFilter.isKotlinClass(context)) {
	return;
	}
	new Matcher().match(methodNode, output);
	}

jacoco/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/KotlinDefaultArgumentsFilter.java

Lines 72 to 86 in 5aabb2e

	public void filter(final MethodNode methodNode,
	final IFilterContext context, final IFilterOutput output) {
	if ((methodNode.access & Opcodes.ACC_SYNTHETIC) == 0) {
	return;
	}
	if (!KotlinGeneratedFilter.isKotlinClass(context)) {
	return;
	}
	if (isDefaultArgumentsMethod(methodNode)) {
	new Matcher().match(methodNode, output, false);
	} else if (isDefaultArgumentsConstructor(methodNode)) {
	new Matcher().match(methodNode, output, true);
	}
	}

[leveretka]

Why do we need a // here?

[Godin]

Otherwise Eclipse JDT Formatter will join lines and the change will look like

                                new AnnotationGeneratedFilter(), new KotlinGeneratedFilter(),
-                               new KotlinLateinitFilter(), new KotlinWhenFilter(),
-                               new KotlinWhenStringFilter(),
+                               new KotlinEnumFilter(), new KotlinLateinitFilter(),
+                               new KotlinWhenFilter(), new KotlinWhenStringFilter(),
                                new KotlinUnsafeCastOperatorFilter(),