[perl #91514] Use correct error msg for ｄｅｆａｕｌｔ

This commit not only mentions ｄｅｆａｕｌｔ (as opposed to ｗｈｅｎ)
in the error message about it being outside a topicalizer, but
also normalises those error messages, making them consistent with
ｃｏｎｔｉｎｕｅ and other loop controls.  It also makes the perldiag
entry for ｗｈｅｎ actually match the error message.

MANIFEST

@@ -4982,6 +4982,7 @@ t/lib/commonsense.t		See if configuration meets basic needs
 t/lib/compmod.pl		Helper for 1_compile.t
 t/lib/croak/mg			Test croak calls from mg.c
 t/lib/croak/op			Test croak calls from op.c
+t/lib/croak/pp_ctl		Test croak calls from pp_ctl.c
 t/lib/croak.t			Test calls to Perl_croak() in the C source.
 t/lib/cygwin.t			Builtin cygwin function tests
 t/lib/dbmt_common.pl		Common functionality for ?DBM_File tests

op.c

@@ -6150,6 +6150,7 @@ S_newGIVWHENOP(pTHX_ OP *cond, OP *block,
 	/* This is a default {} block */
 	enterop->op_first = block;
 	enterop->op_flags |= OPf_SPECIAL;
+	o      ->op_flags |= OPf_SPECIAL;
 
 	o->op_next = (OP *) enterop;
     }

op.h

@@ -131,7 +131,8 @@ Deprecated.  Use C<GIMME_V> instead.
 				/*  On OP_DBSTATE, indicates breakpoint
 				 *    (runtime property) */
 				/*  On OP_REQUIRE, was seen as CORE::require */
-				/*  On OP_ENTERWHEN, there's no condition */
+				/*  On OP_(ENTER|LEAVE)WHEN, there's
+				    no condition */
 				/*  On OP_SMARTMATCH, an implicit smartmatch */
 				/*  On OP_ANONHASH and OP_ANONLIST, create a
 				    reference to the new anon hash or array */

pod/perldiag.pod

@@ -682,6 +682,13 @@ quotas or other plumbing problems.
 (F) Only scalar, array, and hash variables may be declared as "my", "our" or
 "state" variables.  They must have ordinary identifiers as names.
 
+=item Can't "default" outside a topicalizer
+
+(F) You have used a C<default> block that is neither inside a
+C<foreach> loop nor a C<given> block.  (Note that this error is
+issued on exit from the C<default> block, so you won't get the
+error if you use an explicit C<continue>.)
+
 =item Can't do inplace edit: %s is not a regular file
 
 (S inplace) You tried to use the B<-i> switch on a special file, such as
@@ -1225,18 +1232,18 @@ expression pattern.  Trying to do this in ordinary Perl code produces a
 value that prints out looking like SCALAR(0xdecaf).  Use the $1 form
 instead.
 
-=item Can't use "when" outside a topicalizer
-
-(F) You have used a when() block that is neither inside a C<foreach>
-loop nor a C<given> block. (Note that this error is issued on exit
-from the C<when> block, so you won't get the error if the match fails,
-or if you use an explicit C<continue>.)
-
 =item Can't weaken a nonreference
 
 (F) You attempted to weaken something that was not a reference.  Only
 references can be weakened.
 
+=item Can't "when" outside a topicalizer
+
+(F) You have used a when() block that is neither inside a C<foreach>
+loop nor a C<given> block.  (Note that this error is issued on exit
+from the C<when> block, so you won't get the error if the match fails,
+or if you use an explicit C<continue>.)
+
 =item Can't x= to read-only value
 
 (F) You tried to repeat a constant value (often the undefined value)

pp_ctl.c

@@ -5024,7 +5024,9 @@ PP(pp_leavewhen)
 
     cxix = dopoptogiven(cxstack_ix);
     if (cxix < 0)
-	DIE(aTHX_ "Can't use when() outside a topicalizer");
+	/* diag_listed_as: Can't "when" outside a topicalizer */
+	DIE(aTHX_ "Can't \"%s\" outside a topicalizer",
+	           PL_op->op_flags & OPf_SPECIAL ? "default" : "when");
 
     POPBLOCK(cx,newpm);
     assert(CxTYPE(cx) == CXt_WHEN);

t/lib/croak/pp_ctl

@@ -0,0 +1,12 @@
+__END__
+# NAME when outside given
+use 5.01;
+when(undef){}
+EXPECT
+Can't "when" outside a topicalizer at - line 2.
+########
+# NAME default outside given
+use 5.01;
+default{}
+EXPECT
+Can't "default" outside a topicalizer at - line 2.