Bug 299900

Description Ayushman Jain 2010-01-18 02:20:10 EST

Build Identifier: I20091210-1301

The null analysis has a flaw while evaluating the OR conditional expression for null info. The variable(s) on the left have their null info properly in place when the analysis of the OR completes, but the same cannot be said about variables(s) on the right. This is because after the analysis of left and right expressions, to combine both we use FlowInfo.conditional, which merges the info when true and the info when false. Within that we use mergedWith() to combine the true info from left expression with true info from right expression.

Note that mergedWith takes the intersection of definitely null variables in the merging streams. So, since the stream of left expression has no info about what is null in the stream of right expression, the variables that are definitely null in right info (when true) are missed out when merging. Ex:

void foo(Object a, Object b) {
  if(a == null || b == null) {
      System.out.print(b.toString());  //Missing potential null access warning
  }
}

In the above case b is definitely null in 'right info when true', but this info about b gets discarded in the merging. This leads to the missing warning(s) further in the code.
Another ex:

void foo(Object a, Object b) {
  if(a == null || b == null) {}
  System.out.print(b.toString());  //Missing potential null access warning
}

In both cases warnings for a are correct.


Reproducible: Always

Steps to Reproduce:
1. in Preference-> Java -> Compiler -> Errors/warnings -> Potential programming problems, enable the warnings null pointer access and potential null pointer access.
2. Try the above two examples.
3. No potential null warning for b, but warning correctly reported for a.