Compiler gives false error with respect to unreachable code

[blickly]

Try compiling the following in the Closure Compiler UI:

// ==ClosureCompiler==
// @compilation_level SIMPLE_OPTIMIZATIONS
// @output_file_name default.js
// ==/ClosureCompiler==

function instanceOf(value, type) {
  try {
    // first try built-in test -- if it succeeds, we're golden.
    if (value instanceof type) {
      return true;
    }
  } catch (exception) {
    if (exception instanceof TypeError) {
      throw exception; // indicates that "type" is not a type
    }
    // Otherwise, assume the exception was caused by 
    // the Firefox 1.0.3 bug.  Work around it.
    return (type === Object);
  }
}

The Compiler issues the following warning:

JSC_UNREACHABLE_CODE: unreachable code at line 7 character 0
  } catch (exception) {

This code is from a Firefox extension (Chickenfoot) where (at least
historically) calling instanceof in this manner could throw a security
exception (or something else, I forget what -- Chickenfoot has been around
since Firefox 1.0) which is why the catch blocks is there and is indeed
reachable.

Original issue reported on code.google.com by bolinfest on 2010-02-20 18:23:26

[blickly]

If anyone is in a similar situation, I was able to do the following as a workaround:

// ==ClosureCompiler==
// @compilation_level SIMPLE_OPTIMIZATIONS
// @output_file_name default.js
// ==/ClosureCompiler==

function instanceOf(value, type) {
  var result;
  try {
    // first try built-in test -- if it succeeds, we're golden.
    result = value instanceof type;
  } catch (exception) {
    if (exception instanceof TypeError) {
      throw exception; // indicates that "type" is not a type
    }
    // Otherwise, assume the exception was caused by 
    // the Firefox 1.0.3 bug.  Work around it.
    return (type === Object);
  }
  return result;
}

Original issue reported on code.google.com by bolinfest on 2010-02-20 18:30:08

[blickly]

Alan, you should be able to fix this pretty easily. Mind taking a look?

Original issue reported on code.google.com by Nicholas.J.Santos on 2010-02-21 19:11:52

[blickly]

Fixed and checked in.

The fix should be available in the next release.

Original issue reported on code.google.com by acleung on 2010-02-22 23:01:22

[blickly]

This issue was closed by revision r114.

Original issue reported on code.google.com by Nicholas.J.Santos on 2010-02-23 01:07:50