[antlr-interest] ANTLR-based Java grammar for javac compiler

[Yang Jiang]

Andy Tripp wrote:
> This seems like a good goal for the new ANTLR tree rewrite mechanism.
> Given the problem of converting a "whatever the java.g author thought
> was reasonable" AST to a "exactly what javac needs" AST, if the
> rewrite mechanism can make this easier than just "doing it by hand", then
> it will be a "good" mechanism, and not just a toy.
>
> Having said that, it looks to me like none of the tree rewrite software
> (e.g. TXL) out there are "good". In other words, they don't look to me 
> like they
> are saving anybody any work, even for this typical use case.
>
> I'm sure Terence could use ANTLR treewalkers to do this pretty quickly,
> but I wonder if Jiang could, too.
Hi Andy,
I agree with you that rewrite from on AST to another AST could be hard :)

But what Simon was saying is to use the Antlr tree rewrite + a custom 
TreeAdaptor to build
the javac tree directly, rather than using the Antlr tree built from the 
tree rewrite grammar with a tree walker,
then generating the javac tree.

>
> Yang Jiang wrote:
>> Yeah, that is the reason.
>> The javac tree is more than just nodes, it also has info like 
>> position, javadoc and line maps etc..
>> It would be pretty easy to simply use the Antlr tree rewrite to build 
>> a tree, but not that easy if
>> the tree structure/specification has already been defined.
>
> When is the tree structure that you need to produce NOT already defined?
For example, the javac node for Compilation unit has three children : 
package annotations, package declaration,  definition list(including 
types imported from "import" and class/interface/enum declaration).

The Java.g grammar I used , from here 
http://antlr.org/grammar/1152141644268/Java.g, defines compliationUnit 
like this:

compilationUnit
    :   annotations
        (   packageDeclaration importDeclaration* typeDeclaration*
        |   classOrInterfaceDeclaration typeDeclaration*
        )
    |   packageDeclaration? importDeclaration* typeDeclaration*
    ;


importDeclaration is NOT part of typeDeclaration here.
Of course, I could tweak the rules to make it generate what I need, but 
it'll just make the grammar hard to read. Besides, I don't want to write 
another Java.g  myself:)


Yang