Bug 147118

Summary:

[compiler][null] Incorrect null analysis involving do_while loop

Product:

[Eclipse Project] JDT

Reporter:

Gordon Henriksen <malanon>

Component:

Core

Assignee:

Maxime Daniel <maxime_daniel>

Status:

VERIFIED FIXED

QA Contact:

Severity:

normal

Priority:

CC:

eclipse, mlists

Version:

3.2

Target Milestone:

3.3 M3

Hardware:

Macintosh

OS:

Mac OS X - Carbon (unsup.)

Whiteboard:

Bug Depends on:

Bug Blocks:

157154

Attachments:

Description	Flags
Suggested fix plus activated test case	none

Description Gordon Henriksen

2006-06-14 17:04:44 EDT

This snippet causes null analysis to raise an incorrect warning. It could probably be slightly more minimal, but this actually makes sense.

	private final static class Node {
		public Node parent;
		public Node sibling;
		public Node child;
	}
	
	public void nullAnalysisBug(Node node) {
		Node cur = node;
		do {
			if (null != cur.child)  // INCORRECT -> warning: The variable cur may be null
				cur = cur.child;
			else if (null != cur.sibling)
				cur = cur.sibling;
			else if (null != cur.parent)
				cur = cur.parent.sibling;
			else
				cur = null; // B
		} while (cur != null);
	}

There are two workarounds:
A. Transforming the loop into a while loop silences the warning, at the cost of an additional comparison at runtime.
B. Transforming the final else statement into a 'break' also averts the warning:

Comment 1 Maxime Daniel

2006-06-15 04:21:19 EDT

Agreed. Following shorter test case should remove any doubt about it:

public class X {
  String f;
  void foo (boolean b) {
    X x = new X();
    do {
      System.out.println(x.f); // yields may be null, whereas it is not first 
                               // time, and is protected by the test thereafter
      if (b) {
        x = null;
      }
    } while (x != null);
  }
}

Added (inactive) test NullReferenceTest#613.

Comment 2 Maxime Daniel

2006-09-19 02:58:26 EDT

Created attachment 50447 [details]
Suggested fix plus activated test case

Mistakenly used the action flow info in input for the looping context late check. Must use the upstream flow instead.
Waiting for 3.3 M2 to be declared before committing.

Comment 3 Maxime Daniel

2006-09-25 06:25:20 EDT

Released for 3.3M3.

Comment 4 Olivier Thomann

2006-10-30 14:00:34 EST

Verified for 3.3 M3 using warm-up build I20061030-0010

Comment 5 Eclipse Webmaster

2007-07-29 09:20:21 EDT

Changing OS from Mac OS to Mac OS X as per bug 185991