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Re: [perl #134058] Bleadperl v5.29.9-123-gaabfeadc64 breaksETHER/signatures-0.13.tar.gz

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From:
Dave Mitchell
Date:
April 26, 2019 21:33
Subject:
Re: [perl #134058] Bleadperl v5.29.9-123-gaabfeadc64 breaksETHER/signatures-0.13.tar.gz
Message ID:
20190426213328.GR6612@iabyn.com
On Wed, Apr 24, 2019 at 10:26:44AM -0700, Karl Williamson via RT wrote:
> If I comment out that assert, it thinks things are syntax errors, so it needs further investigation

The proximate cause is that signatures.xs not clearing PL_lex_stuff at a
certain point.

This Proof of Concept fix passes all tests in blead:

--- signatures.xs-	2019-04-26 21:53:04.430901853 +0100
+++ signatures.xs	2019-04-26 22:07:32.304999812 +0100
@@ -151,6 +151,9 @@
 		return op;
 	}
 
+	assert(PL_lex_stuff == op_sv);
+	PL_lex_stuff = NULL;
+
 	tmp = hook_toke_scan_str (aTHX_ s);
 	tmp2 = hook_parser_get_lex_stuff (aTHX);
 	hook_parser_clear_lex_stuff (aTHX);

but I don't know whether it works with older perls, or why switching
away from the 'stolen' scan_str() to perl's version broke things.

What is happening is that perl parses a sub prototype by using scan_str()
to extract the balanced delimiter:  in thise case the '()'s in

    sub foo ($x) { ... }

scan_str() sets PL_lex_stuff to the extracted prototype, i.e. '$x'
It then creates an OP_CONST whose op_sv is set to PL_lex_stuff, and then
PL_lex_stuff is cleared, i.e. this code in yylex():

		if (have_proto) {
		    NEXTVAL_NEXTTOKE.opval =
                        newSVOP(OP_CONST, 0, PL_lex_stuff);
		    PL_lex_stuff = NULL;
		    force_next(THING);
		}

B-Hooks-Parser / signatures.xs hook into the ck_foo() mechanism, so that
the hook is called for the OP_CONST in the newSVOP() above. The hook
revisits the lexing stream that's just been processed to confirm whether
it is of the form 'sub maybe_a_name (...)', using calls to
hook_toke_skipspace() etc to extract and skip over the bits + pieces and
to confirm that they form a sub declaration rather than anything else.

At this point it calls scan_str() to skip over the prototype. Here it goes
wrong, because PL_lex_stuff is still set, which causes scan_str() to think
it's scanning the second part of a s/// or tr///, and so sets PL_lex_repl
instead of PL_lex_stuff.

So that diff above just ensures that PL_lex_stuff is NULL before calling
scan_str() to skip over the prototype/signature again.

-- 
Monto Blanco... scorchio!

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