[antlr-interest] Line and column numbers in rewrite rules

[Andreas Stefik]

It looks like I missed a few posts on this topic from a few days ago
(Thanks, Jim!)

The suggestion appears to pass, for a tree grammar rule like:

expression    returns[ExpressionValue eval]
    :
        ^(PLUS left = expression right = expression)

to use $e.tree and then get the line and column info.

On the Java target, the following:

CommonTree tree = $left.tree;

generates:

CommonTree tree = (left!=null?((CommonTree)left.tree):null);

But there is no variable called tree (apparently). There is, however, a
"getTree()" function, but it doesn't look like ANTLR automatically
translates it into that form, so I assume that's not its intended use. If,
however, I hack the generated code and put in something similar to

(CommonTree)left.getTree()) the result appears to always be null.

Jim, does your solution have some preconditions I'm not seeing?

Andy
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