Integrate change #8586 from maint-5.6/perl.

make the BOM detection code not call tell() until it has to
(meant to fix esoteric compatibility issues where PL_rsfp
is overridden)

p4raw-link: @8586 on //depot/maint-5.6/perl: 7b18f0b9fd425b568b9ff49e195709c84e549b71

p4raw-id: //depot/perl@8589
p4raw-integrated: from //depot/maint-5.6/perl@8588 'merge in' toke.c
	(@8579..)

1 files changed, 30 insertions, 29 deletions

diff --git a/toke.c b/toke.c
index a85a7252a9..a1f521d1ed 100644
--- a/toke.c
+++ b/toke.c
@@ -2572,7 +2572,32 @@ Perl_yylex(pTHX)
 	}
 	do {
 	    bof = PL_rsfp ? TRUE : FALSE;
-	    if (bof) {
+	    if ((s = filter_gets(PL_linestr, PL_rsfp, 0)) == Nullch) {
+	      fake_eof:
+		if (PL_rsfp) {
+		    if (PL_preprocess && !PL_in_eval)
+			(void)PerlProc_pclose(PL_rsfp);
+		    else if ((PerlIO *)PL_rsfp == PerlIO_stdin())
+			PerlIO_clearerr(PL_rsfp);
+		    else
+			(void)PerlIO_close(PL_rsfp);
+		    PL_rsfp = Nullfp;
+		    PL_doextract = FALSE;
+		}
+		if (!PL_in_eval && (PL_minus_n || PL_minus_p)) {
+		    sv_setpv(PL_linestr,PL_minus_p ? ";}continue{print" : "");
+		    sv_catpv(PL_linestr,";}");
+		    PL_oldoldbufptr = PL_oldbufptr = s = PL_linestart = SvPVX(PL_linestr);
+		    PL_bufend = SvPVX(PL_linestr) + SvCUR(PL_linestr);
+		    PL_minus_n = PL_minus_p = 0;
+		    goto retry;
+		}
+		PL_oldoldbufptr = PL_oldbufptr = s = PL_linestart = SvPVX(PL_linestr);
+		sv_setpv(PL_linestr,"");
+		TOKEN(';');	/* not infinite loop because rsfp is NULL now */
+	    }
+	    /* if it looks like the start of a BOM, check if it in fact is */
+	    else if (bof && (!*s || *(U8*)s == 0xEF || *(U8*)s >= 0xFE)) {
 #ifdef PERLIO_IS_STDIO
 #  ifdef __GNU_LIBRARY__
 #    if __GNU_LIBRARY__ == 1 /* Linux glibc5 */
@@ -2592,38 +2617,14 @@ Perl_yylex(pTHX)
 		 * Workaround?  Maybe attach some extra state to PL_rsfp?
 		 */
 		if (!PL_preprocess)
-		    bof = PerlIO_tell(PL_rsfp) == 0;
+		    bof = PerlIO_tell(PL_rsfp) == SvCUR(PL_linestr);
 #else
-		bof = PerlIO_tell(PL_rsfp) == 0;
+		bof = PerlIO_tell(PL_rsfp) == SvCUR(PL_linestr);
 #endif
-	    }
-	    s = filter_gets(PL_linestr, PL_rsfp, 0);
-	    if (s == Nullch) {
-	      fake_eof:
-		if (PL_rsfp) {
-		    if (PL_preprocess && !PL_in_eval)
-			(void)PerlProc_pclose(PL_rsfp);
-		    else if ((PerlIO *)PL_rsfp == PerlIO_stdin())
-			PerlIO_clearerr(PL_rsfp);
-		    else
-			(void)PerlIO_close(PL_rsfp);
-		    PL_rsfp = Nullfp;
-		    PL_doextract = FALSE;
-		}
-		if (!PL_in_eval && (PL_minus_n || PL_minus_p)) {
-		    sv_setpv(PL_linestr,PL_minus_p ? ";}continue{print" : "");
-		    sv_catpv(PL_linestr,";}");
-		    PL_oldoldbufptr = PL_oldbufptr = s = PL_linestart = SvPVX(PL_linestr);
+		if (bof) {
 		    PL_bufend = SvPVX(PL_linestr) + SvCUR(PL_linestr);
-		    PL_minus_n = PL_minus_p = 0;
-		    goto retry;
+		    s = swallow_bom((U8*)s);
 		}
-		PL_oldoldbufptr = PL_oldbufptr = s = PL_linestart = SvPVX(PL_linestr);
-		sv_setpv(PL_linestr,"");
-		TOKEN(';');	/* not infinite loop because rsfp is NULL now */
-	    } else if (bof) {
-		PL_bufend = SvPVX(PL_linestr) + SvCUR(PL_linestr);
-		s = swallow_bom((U8*)s);
 	    }
 	    if (PL_doextract) {
 		if (*s == '#' && s[1] == '!' && instr(s,"perl"))