kawa 1.14 causes java.lang.IllegalAccessException

[Per Bothner]

On 10/07/2013 12:36 AM, Ito Kazumitsu wrote:
> Could you explain this phenomenon?
>
> $ java -cp kawa-1.13.jar kawa.repl test.scm
> abc
> $ java -cp kawa-1.13.jar kawa.repl --script test.scm
> test.scm:2:1: warning - no known slot 'append' in java.lang.Object
> test.scm:3:1: warning - no known slot 'setLength' in java.lang.Object
> abc

This part is easy to explain:  In the first case, test.scm is
processed in "whole-module mode" - the entire file is read and
processed as a unit.  Therefore the Kawa compiler knows that sb
has no other assignments except the initial 'define', so Kawa can
easily infer the type to be java.lang.StringBuilder.

When using the --script flag (or the -f flag) then test.scm is
processed in "line-at-a-time mode".  Each command is individually
read, analyzed, and executed.  In that case the Kawa compiler
can't know there won't be later:
   (set! sb "foo")
Therefore Kawa has to defer method resolution until runtime,
and call the method using runtime reflection.

True, when it comes to the calls to append and setLength is it
easy to see that sb must still have its initial value and type.
But what if the call to append is inside a function - which might
get called after sb has been re-assigned?  It becomes compliucated,
especially if also want to handle loops, which are inlined function
calls.

Two ways to fix the problem (not counting using whole-module mode):

(1) Specify that sb is constant:

(define-constant sb (java.lang.StringBuilder))

(2) Specify an explicit type:

(define sb ::java.lang.StringBuilder (java.lang.StringBuilder))

Even if we're using run-time reflection, we shouldn't be getting
the IllegalAccessException.  The problem is that setLength is actually
defined in AbstractStringBuilder, which is a package-private superclass
to both StringBuilder and StringBuffer.  I'm not clear on how to avoid
the problem, but I'll dig into it.  Even more puzzling is what changed
between 1.13 and 1.14 to break it.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/