Review

13

/home/eko/MUBench/MUBench/checkouts/closure/319/original-src/com/google/javascript/jscomp/CheckSideEffects.java

visit(NodeTraversal, Node, Node)

class CheckSideEffects {
  public void visit(NodeTraversal t, Node n, Node parent) {
    // VOID nodes appear when there are extra semicolons at the BLOCK level.
    // I've been unable to think of any cases where this indicates a bug,
    // and apparently some people like keeping these semicolons around,
    // so we'll allow it.
    if (n.getType() == Token.EMPTY ||
        n.getType() == Token.COMMA) {
      return;
    }

    if (parent == null)
      return;

    int pt = parent.getType();
    if (pt == Token.COMMA) {
      Node gramps = parent.getParent();
      if (gramps.getType() == Token.CALL &&
          parent == gramps.getFirstChild()) {
        // Semantically, a direct call to eval is different from an indirect
        // call to an eval. See Ecma-262 S15.1.2.1. So it's ok for the first
        // expression to a comma to be a no-op if it's used to indirect
        // an eval.
        if (n == parent.getFirstChild() &&
            parent.getChildCount() == 2 &&
            n.getNext().getType() == Token.NAME &&
            "eval".equals(n.getNext().getString())) {
          return;
        }
      }

      if (n == parent.getLastChild()) {
        for (Node an : parent.getAncestors()) {
          int ancestorType = an.getType();
          if (ancestorType == Token.COMMA)
            continue;
          if (ancestorType != Token.EXPR_RESULT &&
              ancestorType != Token.BLOCK)
            return;
          else
            break;
        }
      }
    } else if (pt != Token.EXPR_RESULT && pt != Token.BLOCK) {
      if (pt == Token.FOR && parent.getChildCount() == 4 &&
          (n == parent.getFirstChild() ||
           n == parent.getFirstChild().getNext().getNext())) {
        // Fall through and look for warnings for the 1st and 3rd child
        // of a for.
      } else {
        return;  // it might be ok to not have a side-effect
      }
    }
    if (NodeUtil.isSimpleOperatorType(n.getType()) ||
        !NodeUtil.mayHaveSideEffects(n, t.getCompiler())) {
      if (n.isQualifiedName() && n.getJSDocInfo() != null) {
        // This no-op statement was there so that JSDoc information could
        // be attached to the name. This check should not complain about it.
        return;
      } else if (NodeUtil.isExpressionNode(n)) {
        // we already reported the problem when we visited the child.
        return;
      }

      String msg = "This code lacks side-effects. Is there a bug?";
      if (n.getType() == Token.STRING) {
        msg = "Is there a missing '+' on the previous line?";
      }

      t.getCompiler().report(
          t.makeError(n, level, USELESS_CODE_ERROR, msg));
    }
  }

}