[PATCH] Compile-time hooks into lexical scoping

The attached patches make it possible for extensions to hook into perl's
lexical scope mechanism at compile time. This would allow things like my
SCOPECHECK and Florian's @{^COMPILE_SCOPE_CONTAINER} to be implemented
as CPAN modules[1]. Usage is like this (from XS):

    STATIC void my_start_hook(pTHX_ int full);
    STATIC void my_pre_end_hook(pTHX_ OP **o);
    STATIC void my_post_end_hook(pTHX_ OP **o);
    STATIC void my_eval_hook(pTHX_ OP *const o);
    STATIC BHK my_hooks;

    BOOT:
        BhkENTRY_set(&my_hooks, start, my_start_hook);
        BhkENTRY_set(&my_hooks, pre_end, my_pre_end_hook);
        BhkENTRY_set(&my_hooks, post_end, my_post_end_hook);
        BhkENTRY_set(&my_hooks, eval, my_eval_hook);
        Perl_blockhook_register(aTHX_ &my_hooks);

This will cause

    - my_start_hook to be called at the start of compiling every lexical
      scope, with the 'full' parameter from Perl_block_start.

    - my_pre_end_hook to be called at the end of compiling every lexical
      scope, *before* the compile-time stack is unwound, with o pointing
      to the root OP for the scope. It is a double pointer so the hook
      can substitute a different OP if it needs to.

    - my_post_end_hook to be called *after* the stack is unwound.

    - my_eval_hook to be called just before compiling an
      eval/do/require, with o set to the OP that requested the eval.

The patches are rebased against current blead, and the branch has been
pushed to http://github.com/mauzo/perl/tree/blockhooks . I hope
including a whole lot of patches in one mail like this is OK: it seemed
easier than separate mails for each patch, since they all go together.

Ben

[1] Implementing the rest of the Perl 6 blocks on CPAN would require at
least one more patch, to allow extensions to create pad entries.

• [PATCH] Compile-time hooks into lexical scoping by Ben Morrow
• Re: [PATCH] Compile-time hooks into lexical scoping by Jesse Vincent
• Re: [PATCH] Compile-time hooks into lexical scoping by Ben Morrow
• Re: [PATCH] Compile-time hooks into lexical scoping by Zefram
• Re: [PATCH] Compile-time hooks into lexical scoping by Ben Morrow