[patch] 6746458 support for exotic identifiers (identifier superquote)

[John Rose]

Each language has its own rules for forming identifiers of functions,  
variables, and types.  The JVM allows almost total freedom, at the  
bytecode level, for forming names of methods, fields, and classes.   
So far so good.  If a language (say, Lisp, Smalltalk, Ruby, or Scala)  
wants to encode its names directly in the JVM, it runs into two  
problems.  The first is the small number of remaining restrictions on  
JVM bytecode names; this can easily be overcome by lightweight  
mangling as outlined in this blog post:
   http://blogs.sun.com/jrose/entry/symbolic_freedom_in_the_vm

The second problem is the fact that the language runtime is probably  
written largely in Java, which means that the "exotic" names in the  
language cannot be directly implemented by Java classes, methods, and  
fields.  In practice, this difficulty forces language implementors to  
mangle their names not for the JVM (which is permissive) but for Java  
(which is restrictive).

The solution to the second problem is to provide an "escape" syntax  
(similar to that of Lisp and other languages) which allows an  
arbitrary string to pass through the language scanner as a simple  
identifier token instead of some other token (or an unscannable mess).

We propose the syntax #"foo".  See example implementation here and  
enclosed in this message:
   http://hg.openjdk.java.net/mlvm/mlvm/langtools/file/tip/quid.patch

The javac frontend should accept any quoted string immediately  
following '#' (with no intervening space), interpreting normal string  
escape sequences, and taking the resulting string exactly as the  
spelling of a normal identifier.  Keywords like 'int' should not be  
recognized.  Strings which risk being illegal at the JVM level must  
be rejectedi immediately; this simply means rejecting the empty  
string and strings which contain any of the characters "/.;<>[".

This design is neutral toward mangling schemes but supports the one  
described in the blog entry mentioned above.

(Thanks for Alex Buckley and Jon Gibbons for helping me figure this  
out, and especially for suggesting a reasonable syntax.)

-- John

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