Implement parse tree pretty-printing a la Cpp runtime in other runtimes

The C++ runtime supports generating string representations of the parse tree in two forms: the standard all-in-one-line Lisp-ish expression, and a pretty-printed version, which splits the Lisp expression into multiple lines and indents subexpressions. None of the other runtime targets have the pretty-printing capability. It would be quite handy for human-focused results, including the unit test systems of the grammars-v4 collection.

I suggest we implement the C++ runtime behavior in all the other runtimes.

[parrt]

I have to generate json from parse trees to serialize across socket from server to client for antlr lab.

[KvanTTT]

We’ve encoutered the similar issue several times:

• https://github.com/antlr/antlr4/issues/1502
• https://github.com/antlr/antlr4/pull/2340
• https://github.com/antlr/antlr4/pull/3229

Yes I guess it seems like there’s really no reason to add code that I will have to support for the next decade or so, when there’s no strong need.

It’s useful feature, but I consider the suggested format with a lot of confusing parentheses is confusing. I suggest using tree with indents:

parse 
 sql_stmt_list 
  sql_stmt 
   select_stmt 
    select_core 
     select    
     result_column 
      expr 
       column_name 
        any_name 
         id
     ,    
     result_column 
      expr 
       column_name 
        any_name 
         first_name
     from    
     table_or_subquery 
      table_name 
       any_name 
        users
  ;
 <EOF>

What’s a JSON generator actually? I have to admit I haven’t heard about that before.

It’s useful feature especially for client-server scenarious and other scenarios where serilization is required. Also, it’s useful for tree comparison in tests.