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Bug 507001

Summary:	Warning The method xxx from the type X is never used locally is shown for code using xxx from another class.
Product:	[Eclipse Project] JDT	Reporter:	Daniel Friederich <danielfriederich>
Component:	Core	Assignee:	JDT-Core-Inbox <jdt-core-inbox>
Status:	CLOSED WONTFIX	QA Contact:	Stephan Herrmann <stephan.herrmann>
Severity:	normal
Priority:	P3	CC:	jarthana, stephan.herrmann
Version:	4.6
Target Milestone:	---
Hardware:	PC
OS:	Linux
Whiteboard:	stalebug

Description Daniel Friederich

2016-11-03 15:23:11 EDT

Technically the message is not actually wrong as it is really not used locally.
But my expectation with this message is that it is save to remove the function (which is also the quickfix for it), but in this case this breaks the code.

I saw this warning from some java library in github (https://github.com/vidstige/jadb.git).
Simplified the issue is shown for the PubDef.hello method in this code:
public class Def {
	static private class PrivDef {
		static public class PubDef {
			public void hello() {
				System.out.println("Hello");
			}
		}
		PubDef getPubDef() {
			return new PubDef();
		}
	}
	PrivDef.PubDef getPubDef() {
		return new PrivDef().getPubDef();
	}
}

However another class can call hello:

public class User {
	static public int main(char[] args) {
		Def d = new Def();
		d.getPubDef().hello();
		return 0;
	}
}

Hence it is not correct to remove it.

Comment 1 Stephan Herrmann

2016-11-03 16:30:13 EDT

Geewiz, always another surprise with Java.

Conceptually, that's what I'd call an API leak: getPubDef() makes an inaccessible type accessible (kind-of, see below).

Interesting twist: User cannot name Def.Privdef.PubDef but it can use it. Wow!
Hint: try extracting "d.getPubDef()" to a local variable => Boom!

Put differently, java seems to allow accessing a method of an inaccessible type.

=> Our assumption that membership in a private type restricts the accessibility is wrong.

OTOH, I'd definitely not accept the above as good design. So maybe the warning (and resulting error if you remove the method) is a good thing to alert folks of the bad design :p


On a related note: I just surfed JLS to figure out what should change for Jigsaw, and indeed could not find any requirement that the receiver type of a field access or method invocation must be accessible. Looks like a spec bug, if you ask me.

Comment 2 Eclipse Genie

2020-05-07 13:38:16 EDT

This bug hasn't had any activity in quite some time. Maybe the problem got resolved, was a duplicate of something else, or became less pressing for some reason - or maybe it's still relevant but just hasn't been looked at yet. As such, we're closing this bug.

If you have further information on the current state of the bug, please add it and reopen this bug. The information can be, for example, that the problem still occurs, that you still want the feature, that more information is needed, or that the bug is (for whatever reason) no longer relevant.

--
The automated Eclipse Genie.