[JEP 488][Preview][Primitive Patterns] ECJ crashes compiling switch over void typed selector expression

[srikanth-sankaran]

Found by code inspection and white box testing:

ECJ crashes compiling the following code; javac complains error: the switch statement does not cover all possible input values

public class X {
	public static void main(String[] args) {
		switch (main(null)) {
		
		}
	}
}

Stack trace on master (problem can be seen from 4.34 M2)

Caused by: java.util.EmptyStackException
	at java.base/java.util.Stack.peek(Stack.java:103)
	at org.eclipse.jdt.internal.compiler.codegen.OperandStack.peek(OperandStack.java:123)
	at org.eclipse.jdt.internal.compiler.codegen.CodeStream.dup(CodeStream.java:1082)
	at org.eclipse.jdt.internal.compiler.ast.SwitchStatement.generateCodeSwitchPatternPrologue(SwitchStatement.java:850)
	at org.eclipse.jdt.internal.compiler.ast.SwitchStatement.generateCode(SwitchStatement.java:708)
	at org.eclipse.jdt.internal.compiler.ast.AbstractMethodDeclaration.generateCode(AbstractMethodDeclaration.java:395)
	at org.eclipse.jdt.internal.compiler.ast.AbstractMethodDeclaration.generateCode(AbstractMethodDeclaration.java:331)
	at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.generateCode(TypeDeclaration.java:773)
	at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.generateCode(TypeDeclaration.java:843)
	at org.eclipse.jdt.internal.compiler.ast.CompilationUnitDeclaration.generateCode(CompilationUnitDeclaration.java:403)
	at org.eclipse.jdt.internal.compiler.Compiler.resolve(Compiler.java:1119)
	at org.eclipse.jdt.internal.compiler.Compiler.resolve(Compiler.java:1155)
	at org.eclipse.jdt.internal.core.CompilationUnitProblemFinder.process(CompilationUnitProblemFinder.java:292)

[srikanth-sankaran]

From a cursory reading of JEP488 and Draft JLS changes I haven't been able to ascertain the right behavior here:

14.11 has been modified to say The type of the selector expression may be any type. and then if it is void what ? I haven't been able to determine.

[srikanth-sankaran]

Not sure this should compile, but does with both javac and ECJ:

public class X {
	public static void main(String[] args) {
		switch (null) {
			case null -> System.out.println("Null");
			default-> System.out.println("Default");
		}
	}
}

Not sure this should not (two nots there) compile, but doesn't with both ECJ and javac: Both complain about missing default

public class X {
	public static void main(String[] args) {
		switch (null) {
			case null -> System.out.println("Null");
			// default-> System.out.println("Default");
		}
	}
}