PrimAndStringOp bug in AstJavaTypeInference

[vazexqi]

Problem

I was using AstJavaTypeInference and discovered a bug with the way that string + primitives are handled. I've included a test case in the pull request but here's the gist of it

package javaonepointfive;

public class TypeInferencePrimAndStringOp {
  public static void main(String[] args) {
    int a = 2;
    String result = "a" + a;
  }
}

Trying to infer the type of result ends with a Unexpected type: class com.ibm.wala.analysis.typeInference.JavaPrimitiveType exception.

Cause

After tracing it down, I found that PrimAndStringOp uses a field call stringClass in AstJavaTypeInference but that field does not get a chance to be initialized before it is used. That is because the first line in AstJavaTypeInference is a call to super that initializes the AbstractFixedPointSolver, which calls the initialize() and solve() functions, which in turn, calls the evaluate function in PrimAndStringOp.

Here's the original constructor for AstJavaTypeInference:

  public AstJavaTypeInference(IR ir, IClassHierarchy cha, boolean doPrimitives) {
    super(ir, cha, JavaPrimitiveType.BOOLEAN, doPrimitives);
    this.stringClass = cha.lookupClass(TypeReference.JavaLangString);

(Possible) Solution

I used lazy initialization for stringClass to ensure that it is initialized when it is first used in the evaluate function in PrimAndStringOp.

  IClass getStringClass() {
    if (stringClass == null) {
      this.stringClass = cha.lookupClass(TypeReference.JavaLangString);
    }
    return stringClass;
  }

[msridhar]

Nice report and fix; merged. Thanks!