[java] UnnecessaryCast: ContextedRuntimeException when parsing switch expression with lambdas

[Ledmington]

Affects PMD Version: 7.18.0

Rule: UnnecessaryCast

Description:
When launching pmd, it crashes with a ContextedRuntimeException, caused by a ClassCastException, when applying the rule UnnecessaryCast. By reading through the error message, it seems to me that the problem is that I am using a switch expression where the function expects a lambda.

Exception Stacktrace:

...
Exception applying rule UnnecessaryCast on file /home/fbarbari/prova/emu/core/src/main/java/com/ledmington/emu/X86Cpu.java, continuing with next rule
org.apache.commons.lang3.exception.ContextedRuntimeException: java.lang.ClassCastException: class net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression cannot be cast to class net.sourceforge.pmd.lang.java.ast.InvocationNode (net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression and net.sourceforge.pmd.lang.java.ast.InvocationNode are in unnamed module of loader org.gradle.internal.classloader.VisitableURLClassLoader @5fe469d4)
Exception Context:
        [1:Rule applied on node=!debug only! [CastExpression:574:23](long) imm.asInt()]
---------------------------------
        at net.sourceforge.pmd.util.AssertionUtil.contexted(AssertionUtil.java:257)
        at net.sourceforge.pmd.lang.rule.internal.RuleApplicator.applyOnIndex(RuleApplicator.java:79)
        at net.sourceforge.pmd.lang.rule.internal.RuleApplicator.apply(RuleApplicator.java:57)
        at net.sourceforge.pmd.lang.rule.internal.RuleSets.apply(RuleSets.java:183)
        at net.sourceforge.pmd.lang.impl.PmdRunnable.processSource(PmdRunnable.java:140)
        at net.sourceforge.pmd.lang.impl.PmdRunnable.run(PmdRunnable.java:80)
        at java.base@21.0.8/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
        at java.base@21.0.8/java.util.concurrent.FutureTask.run(FutureTask.java:317)
        at java.base@21.0.8/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
        at java.base@21.0.8/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
        at java.base@21.0.8/java.lang.Thread.run(Thread.java:1583)
Caused by: java.lang.ClassCastException: class net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression cannot be cast to class net.sourceforge.pmd.lang.java.ast.InvocationNode (net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression and net.sourceforge.pmd.lang.java.ast.InvocationNode are in unnamed module of loader org.gradle.internal.classloader.VisitableURLClassLoader @5fe469d4)
        at net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryCastRule.isCastDeterminingReturnOfLambda(UnnecessaryCastRule.java:281)
        at net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryCastRule.isCastUnnecessary(UnnecessaryCastRule.java:143)
        at net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryCastRule.visit(UnnecessaryCastRule.java:111)
        at net.sourceforge.pmd.lang.java.ast.ASTCastExpression.acceptVisitor(ASTCastExpression.java:33)
        at net.sourceforge.pmd.lang.java.ast.AbstractJavaNode.acceptVisitor(AbstractJavaNode.java:38)
        at net.sourceforge.pmd.lang.java.rule.AbstractJavaRule.apply(AbstractJavaRule.java:30)
        at net.sourceforge.pmd.lang.rule.RuleReference.apply(RuleReference.java:413)
        at net.sourceforge.pmd.lang.rule.internal.RuleApplicator.applyOnIndex(RuleApplicator.java:77)
        ... 9 more
Exception occurred on node !debug only! [CastExpression:574:23](long) imm.asInt()
Exception applying rule UnnecessaryCast on file /home/fbarbari/prova/emu/core/src/main/java/com/ledmington/emu/X86Cpu.java, continuing with next rule
org.apache.commons.lang3.exception.ContextedRuntimeException: java.lang.ClassCastException: class net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression cannot be cast to class net.sourceforge.pmd.lang.java.ast.InvocationNode (net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression and net.sourceforge.pmd.lang.java.ast.InvocationNode are in unnamed module of loader org.gradle.internal.classloader.VisitableURLClassLoader @5fe469d4)
Exception Context:
        [1:Rule applied on node=!debug only! [CastExpression:573:22](long) imm.asByte()]
---------------------------------
        at net.sourceforge.pmd.util.AssertionUtil.contexted(AssertionUtil.java:257)
        at net.sourceforge.pmd.lang.rule.internal.RuleApplicator.applyOnIndex(RuleApplicator.java:79)
        at net.sourceforge.pmd.lang.rule.internal.RuleApplicator.apply(RuleApplicator.java:57)
        at net.sourceforge.pmd.lang.rule.internal.RuleSets.apply(RuleSets.java:183)
        at net.sourceforge.pmd.lang.impl.PmdRunnable.processSource(PmdRunnable.java:140)
        at net.sourceforge.pmd.lang.impl.PmdRunnable.run(PmdRunnable.java:80)
        at java.base@21.0.8/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
        at java.base@21.0.8/java.util.concurrent.FutureTask.run(FutureTask.java:317)
        at java.base@21.0.8/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
        at java.base@21.0.8/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
        at java.base@21.0.8/java.lang.Thread.run(Thread.java:1583)
Caused by: java.lang.ClassCastException: class net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression cannot be cast to class net.sourceforge.pmd.lang.java.ast.InvocationNode (net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression and net.sourceforge.pmd.lang.java.ast.InvocationNode are in unnamed module of loader org.gradle.internal.classloader.VisitableURLClassLoader @5fe469d4)
        at net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryCastRule.isCastDeterminingReturnOfLambda(UnnecessaryCastRule.java:281)
        at net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryCastRule.isCastUnnecessary(UnnecessaryCastRule.java:143)
        at net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryCastRule.visit(UnnecessaryCastRule.java:111)
        at net.sourceforge.pmd.lang.java.ast.ASTCastExpression.acceptVisitor(ASTCastExpression.java:33)
        at net.sourceforge.pmd.lang.java.ast.AbstractJavaNode.acceptVisitor(AbstractJavaNode.java:38)
        at net.sourceforge.pmd.lang.java.rule.AbstractJavaRule.apply(AbstractJavaRule.java:30)
        at net.sourceforge.pmd.lang.rule.RuleReference.apply(RuleReference.java:413)
        at net.sourceforge.pmd.lang.rule.internal.RuleApplicator.applyOnIndex(RuleApplicator.java:77)
        ... 9 more
Exception occurred on node !debug only! [CastExpression:573:22](long) imm.asByte()

> Task :core:pmdMain FAILED
/home/fbarbari/prova/emu/core/src/main/java/com/ledmington/emu/X86Cpu.java      -       ContextedRuntimeException: java.lang.ClassCastException: class net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression cannot be cast to class net.sourceforge.pmd.lang.java.ast.InvocationNode (net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression and net.sourceforge.pmd.lang.java.ast.InvocationNode are in unnamed module of loader org.gradle.internal.classloader.VisitableURLClassLoader @5fe469d4)
Exception Context:
        [1:Rule applied on node=!debug only! [CastExpression:574:23](long) imm.asInt()]
---------------------------------
/home/fbarbari/prova/emu/core/src/main/java/com/ledmington/emu/X86Cpu.java      -       ContextedRuntimeException: java.lang.ClassCastException: class net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression cannot be cast to class net.sourceforge.pmd.lang.java.ast.InvocationNode (net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression and net.sourceforge.pmd.lang.java.ast.InvocationNode are in unnamed module of loader org.gradle.internal.classloader.VisitableURLClassLoader @5fe469d4)
Exception Context:
        [1:Rule applied on node=!debug only! [CastExpression:573:22](long) imm.asByte()]
---------------------------------

Code Sample demonstrating the issue:
This is the problematic part, in particular the switch returning lambdas (at core/src/main/java/com/ledmington/emu/X86Cpu.java, line 568).

private void opSX(final Register64 op1, final Immediate imm, final BiFunction<Long, Long, Long> task) {
	op(
			() -> rf.get(op1),
			// FIXME: ugly
			switch (imm.bits()) {
				case 8 -> () -> (long) imm.asByte();
				case 32 -> () -> (long) imm.asInt();
				default -> throw new IllegalArgumentException(String.format("Unknown immediate: %s.", imm));
			},
			task,
			result -> rf.set(op1, result),
			true);
}

Steps to reproduce:

Please provide detailed steps for how we can reproduce the bug.

1. git clone https://github.com/Ledmington/emu.git
2. cd emu
3. git checkout 9ec3ef3f4982f7e779e0e8ea1812fb034a4919e1
4. ./gradlew clean :core:pmdMain

Running PMD through: Gradle

[Ledmington]

If it may be of any help, I tried changing that switch into this (a lambda with a switch instead of a switch returning lambdas):

...
() -> switch (imm.bits()) {
	case 8 -> (long) imm.asByte();
	case 32 -> (long) imm.asInt();
	default -> throw new IllegalArgumentException(String.format("Unknown immediate: %s.", imm));
},
...

and the error, meaning PMD crashing, went away. It still complained about the unnecessary casts.

[Ledmington]

Minor double update.

1. This bug affects also 7.19.0.

2. While trying to mess around with the PMD codebase to open a PR, I found a smaller reproducer:

import java.util.function.Supplier;
public class Foo {
    public void bar(int x) {
        foo(
            switch(x) {
                case 0 -> () -> (long) 1;
                case 1 -> () -> (long) 2;
                default -> throw new Error();
            }
        );
    }

    public void foo(Supplier<Long> sup) {
        // intentionally empty
    }
}

[oowekyala]

Thank you for the complete reproducer. I'm working on it

[Ledmington]

Thank you very much for the fix @adangel and @oowekyala. Happy new Year!