Allow => to quote built-in keywords across lines

If I have a sub I can use its name as a bareword as long as I suffix
it with =>, even if the => is on the next line:

$ ./perl -Ilib -e 'sub tim; warn tim' -e '=>'
tim at -e line 1.

If I want to use a built-in keyword’s name as a bareword, I can put =>
after it:

$ ./perl -Ilib -e 'warn time =>'
time at -e line 1.

But if I combine the two (keyword + newline), it does not work:

$ ./perl -Ilib -e 'warn time' -e ' =>'
1373611283 at -e line 1.

unless I override the keyword:

$ ./perl -Ilib -Msubs=time -e 'warn time' -e ' =>'
time at -e line 1.

=> after a bareword is checked for in two places in toke.c.  The first
comes before a comment saying ‘NO SKIPSPACE BEFORE HERE!’; it only
skips spaces and finds a => on the same line.  The second comes later;
it skips vertical space and comments, too.

But the second check is in a code path that is not reached by keywords
that are not overridden (as is the ‘NO SKIPSPACE’ comment).

This commit adds an extra check for built-in keywords after we have
determined that the keyword is not overridden.  In that case, there is
no reason we cannot use skipspace, as we no longer have to worry about
what PL_oldbufptr etc. point to.

This commit leaves __DATA__ and __END__ alone, since they
are special, problematic and controversial.  (See, e.g.,
<https://rt.perl.org/rt3/Ticket/Display.html?id=78348#txn-1234355>.)

1 files changed, 5 insertions, 1 deletions

diff --git a/t/base/lex.t b/t/base/lex.t
index 7ef753807b..7821e763a3 100644
--- a/t/base/lex.t
+++ b/t/base/lex.t
@@ -1,6 +1,6 @@
 #!./perl
 
-print "1..93\n";
+print "1..94\n";
 
 $x = 'x';
 
@@ -443,3 +443,7 @@ y # comment
  ;
 print "not " unless $_ eq 'b';
 print "ok 93 - y <comment> <newline> ...\n";
+
+print "not " unless (time
+                     =>) eq time=>;
+print "ok 94 - => quotes keywords across lines\n";