RE: [PATCH] use 5.010 is ugly; use 5.10.0 warns

From: "Robin Barker" <Robin.Barker@npl.co.uk>
Message-ID: <2C2E01334A940D4792B3E115F95B7226C9D1C3@exchsvr1.npl.ad.local>

p4raw-id: //depot/perl@31978

8 files changed, 30 insertions, 2 deletions

diff --git a/embedvar.h b/embedvar.h
index 15057bce69..93ba32e162 100644
--- a/embedvar.h
+++ b/embedvar.h
@@ -345,6 +345,7 @@
 #define PL_utf8_xdigit		(vTHX->Iutf8_xdigit)
 #define PL_utf8cache		(vTHX->Iutf8cache)
 #define PL_utf8locale		(vTHX->Iutf8locale)
+#define PL_v_string_ok		(vTHX->Iv_string_ok)
 #define PL_warnhook		(vTHX->Iwarnhook)
 #define PL_watchaddr		(vTHX->Iwatchaddr)
 #define PL_watchok		(vTHX->Iwatchok)
@@ -659,6 +660,7 @@
 #define PL_Iutf8_xdigit		PL_utf8_xdigit
 #define PL_Iutf8cache		PL_utf8cache
 #define PL_Iutf8locale		PL_utf8locale
+#define PL_Iv_string_ok		PL_v_string_ok
 #define PL_Iwarnhook		PL_warnhook
 #define PL_Iwatchaddr		PL_watchaddr
 #define PL_Iwatchok		PL_watchok
diff --git a/intrpvar.h b/intrpvar.h
index a6a4a1c641..6fd9b5d3db 100644
--- a/intrpvar.h
+++ b/intrpvar.h
@@ -668,7 +668,9 @@ PERLVARI(Islabs, I32**, NULL)	/* Array of slabs that have been allocated */
 PERLVARI(Islab_count, U32, 0)	/* Size of the array */
 #endif
 
-PERLVARI(Iisarev, HV*, NULL) /* Reverse map of @ISA dependencies */
+PERLVARI(Iisarev, HV*, NULL)	/* Reverse map of @ISA dependencies */
+
+PERLVARI(Iv_string_ok,	bool, FALSE)	/* use/require v_string OK */
 
 /* If you are adding a U8 or U16, see the 'Space' comments above on where
  * there are gaps which currently will be structure padding.  */
diff --git a/perlapi.h b/perlapi.h
index 05cf09ff70..dfe593b70d 100644
--- a/perlapi.h
+++ b/perlapi.h
@@ -726,6 +726,8 @@ END_EXTERN_C
 #define PL_utf8cache		(*Perl_Iutf8cache_ptr(aTHX))
 #undef  PL_utf8locale
 #define PL_utf8locale		(*Perl_Iutf8locale_ptr(aTHX))
+#undef  PL_v_string_ok
+#define PL_v_string_ok		(*Perl_Iv_string_ok_ptr(aTHX))
 #undef  PL_warnhook
 #define PL_warnhook		(*Perl_Iwarnhook_ptr(aTHX))
 #undef  PL_watchaddr
diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 1d2650fdc1..9d79311c08 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -4942,6 +4942,8 @@ C<use 5.006_001>.  This of course won't help: the older Perls
 won't suddenly start understanding newer features, but at least
 they will show a sensible error message indicating the required
 minimum version.
+This warning is suppressed if the C<use 5.x.y> is preceded by a
+C<use 5.006> (see C<use VERSION> in L<perlfunc/use>).
 
 =item Warning: something's wrong
 
diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index 48478f30cf..49df408af4 100644
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -6853,9 +6853,15 @@ avoided, because it leads to misleading error messages under earlier
 versions of Perl that do not support this syntax.  The equivalent numeric
 version should be used instead.
 
+Alternatively, you can use a numeric version C<use 5.006> followed by a
+v-string version like C<use v5.10.1>, to avoid the unintuitive C<use
+5.010_001>. (older perl versions fail gracefully at the first C<use>,
+later perl versions understand the v-string syntax in the second).
+
     use v5.6.1;		# compile time version check
     use 5.6.1;		# ditto
     use 5.006_001;	# ditto; preferred for backwards compatibility
+    use 5.006; use 5.6.1;	# ditto, for compatibility and readability
 
 This is often useful if you need to check the current Perl version before
 C<use>ing library modules that have changed in incompatible ways from
diff --git a/pp_ctl.c b/pp_ctl.c
index 7ecae350ba..673e324dc2 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -3085,11 +3085,18 @@ PP(pp_require)
 
     sv = POPs;
     if ( (SvNIOKp(sv) || SvVOK(sv)) && PL_op->op_type != OP_DOFILE) {
-	if ( SvVOK(sv) && ckWARN(WARN_PORTABLE) )	/* require v5.6.1 */
+	if (!PL_v_string_ok && 
+	    SvVOK(sv) && ckWARN(WARN_PORTABLE) )	/* require v5.6.1 */
 		Perl_warner(aTHX_ packWARN(WARN_PORTABLE),
                         "v-string in use/require non-portable");
 
 	sv = new_version(sv);
+	if (PL_compcv &&
+	    vcmp(sv, sv_2mortal(upg_version(newSVnv(5.006), FALSE))) >= 0)
+		/* version 5.006 recognises 5.x.y in C<use 5.x.y> so
+                   can portably C<use 5.10.0> following C<use 5.006> */
+		    PL_v_string_ok = TRUE;
+
 	if (!sv_derived_from(PL_patchlevel, "version"))
 	    upg_version(PL_patchlevel, TRUE);
 	if (cUNOP->op_first->op_type == OP_CONST && cUNOP->op_first->op_private & OPpCONST_NOVER) {
diff --git a/sv.c b/sv.c
index f94e1bac7d..a07a57f8ae 100644
--- a/sv.c
+++ b/sv.c
@@ -11534,6 +11534,8 @@ perl_clone_using(PerlInterpreter *proto_perl, UV flags,
 	  PTR2UV(PL_watchok));
     }
 
+    PL_v_string_ok	= proto_perl->Iv_string_ok;
+
     if (!(flags & CLONEf_KEEP_PTR_TABLE)) {
         ptr_table_free(PL_ptr_table);
         PL_ptr_table = NULL;
diff --git a/t/lib/warnings/pp_ctl b/t/lib/warnings/pp_ctl
index d27e8963f4..dac35525c6 100644
--- a/t/lib/warnings/pp_ctl
+++ b/t/lib/warnings/pp_ctl
@@ -240,3 +240,8 @@ use warnings;
     eval 'print $foo';
 }
 EXPECT
+########
+# pp_ctl.c
+use warnings;
+eval 'use 5.006; use 5.10.0';
+EXPECT