[antlr-interest] NoViableAltException in ()? rule

[Ingo Maier]

Hi,

for a (x)? the generated code seems not only to check if an x comes
next, but also what can come after (or instead of) that x. If such a
token doesn't follow it throws a NoViableAltException.

For example in the java grammar:

tryBlock: "try"^ compoundStatement (handler)* (finallyClause)?;

If no finally clause comes next, it also checks for possibly following
tokens in the generated typeBlock() method:

switch ( LA(1)) {
  case LITERAL_finally:
  {
    ...
  }
  case FINAL:
  case ABSTRACT:
   ...
     break;


Why? Those following tokens have nothing to do with the rule tryBlock
itself, but only with the enclosing grammar, right?

As a consequence java snippets followed by some non-java text cannot be
parsed without an exception: 

try { /*...*/ } catch(Exception e) { /*...*/ } /* no finally clause */
here comes some text...

When I call tryBlock(), "here" is not expected because of the generated
switch block as pasted above. However, "here" should have nothing to do
with the tryBlock() rule.

Thanks in advance,
Ingo



 
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