[perl #73754] Better error message for PerlIO layer implementations

please find attached a patch against blead originating from [1] ,
that improves the "Layer does not match this perl" error message by
telling the user which IO layer failed and how. I've tested the
patch against a recent bleadperl and even without the modifications
to perldiag.t all tests pass. Still, for completeness, I've patched
perldiag.t as well.

The code is not mine, it was written and posted by Tye McQueen, I've
just tested it [2] and ferry the information. I'm aware that this
patch is too late for 5.12 , but in the sense of improving Perl in
the long run, I hope the change still makes it into a version of
Perl.

-max

[1] http://perlmonks.org/?node_id=829815
[2] Certified Works On My Machine, 2010

1 files changed, 8 insertions, 3 deletions

diff --git a/perlio.c b/perlio.c
index 79b7efae22..547f0b44b2 100644
--- a/perlio.c
+++ b/perlio.c
@@ -1211,13 +1211,18 @@ PerlIO *
 PerlIO_push(pTHX_ PerlIO *f, PERLIO_FUNCS_DECL(*tab), const char *mode, SV *arg)
 {
     if (tab->fsize != sizeof(PerlIO_funcs)) {
-      mismatch:
-	Perl_croak(aTHX_ "Layer does not match this perl");
+	Perl_croak( aTHX_
+	    "%s (%d) does not match %s (%d)",
+	    "PerlIO layer function table size", tab->fsize,
+	    "size expected by this perl", sizeof(PerlIO_funcs) );
     }
     if (tab->size) {
 	PerlIOl *l;
 	if (tab->size < sizeof(PerlIOl)) {
-	    goto mismatch;
+	    Perl_croak( aTHX_
+		"%s (%d) smaller than %s (%d)",
+		"PerlIO layer instance size", tab->size,
+		"size expected by this perl", sizeof(PerlIOl) );
 	}
 	/* Real layer with a data area */
 	if (f) {