[antlr-interest] Bug (difference) in ANTLR 3.2 tree matching.

Michael Matera mike.matera at xilinx.com
Wed Dec 9 10:50:04 PST 2009


Today I noticed a difference in the matching behavior of the tree match
wildcard between ANTLR 3.1.1 and ANTLR 3.2.  I suspect this is a bug
because I don't see anything on the release notes that would tell me
it's a feature.  Here's the problem:

I have a simple grammar with simplified try/catch/always blocks.  I have
a tree parser rule that matches those blocks and looks like this:

testblock : ^('test' body=. failblock=. alwaysblock=.)
  try {
  } catch (MyProgramException e) {
  } always {

When I updated to ANTLR 3.2 I began to notice that my 'fail' blocks were
being executed no matter what (sometimes twice).  When I dumped the
parse tree here's what I found:

  (testbody (print "One"))
  (failure (print "Two"))
  (always (print "Three"))
) null

Since in my language a print statement can't fail what I expect to see
from this parse tree is:


After upgrading to ANTLR 3.2 I see:


For now I am working around the problem by using ANTLR 3.1.1 runtime
against my 3.2 generated code.  I'm not sure that's the best thing to do
but for now it's got me moving forward.

Thanks for any help you can give me!  ANTLR has made a huge impact in my
work, I really love it!


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