ParseXS: refactor: remove $ExtUtils::ParseXS::END

(This commit is part of a series which will extend the AST parse tree
from just representing individual XSUBs to representing the whole XS
file.)

The parser, when parsing an XSUB (but not any other parts of an XS file),
pushes a special token onto the end of the list of lines in
@{$pxs->{line}} which make up the current paragraph. This token,

    $ExtUtils::ParseXS::END = "!End!\n\n";

(along with a trailing ':') is designed  to look like an impossible
keyword which can't actually appear in the source code (due to the
multiple newlines).

It looks like it was originally added in perl5.002 to make the parsing
code easier, but I don't really understand why. It just makes the
parser harder to understand.

So this commit removes it, and just relies on @{$pxs->{line}} being zero
to detect the end of the paragraph. This change doesn't alter the C code
generated from any of the XS files bundled with perl.

Author: iabyn

dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS.pm

@@ -103,10 +103,8 @@ our $AUTHOR_WARNINGS;
 $AUTHOR_WARNINGS = ($ENV{AUTHOR_WARNINGS} || 0)
     unless defined $AUTHOR_WARNINGS;
 
-# "impossible" keyword (multiple newline)
-our $END = "!End!\n\n";
 # Match an XS Keyword
-our $BLOCK_regexp = '\s*(' . $ExtUtils::ParseXS::Constants::XSKeywordsAlternation . "|$END)\\s*:";
+our $BLOCK_regexp = '\s*(' . $ExtUtils::ParseXS::Constants::XSKeywordsAlternation . ")\\s*:";
 
 
 # All the valid fields of an ExtUtils::ParseXS hash object. The 'use

dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS/Node.pm

@@ -1210,12 +1210,8 @@ sub parse {
 
 
 
-        # should just be a fake END token left
-        die "Internal error: bad END token\n"
-            unless $pxs->{line}
-                  && @{$pxs->{line}} == 1
-                  && $pxs->{line}[0] eq "$ExtUtils::ParseXS::END:";
-        pop @{$pxs->{line}};
+        die "Internal error: unexpectedly not at EOF\n"
+                  if @{$pxs->{line}};
 
         $pxs->{seen_an_XSUB} = 1; # encountered at least one XSUB
     } # END 'PARAGRAPH' 'while' loop
@@ -1786,13 +1782,6 @@ sub parse {
         or return;
     push @{$self->{kids}}, $decl;
 
-    # Append a fake EOF-keyword line. This makes it easy to do "all lines
-    # until the next keyword" style loops, since the fake END line (which
-    # includes a \n so it can't appear in the wild) is also matched as a
-    # keyword.
-    push(@{ $pxs->{line} }, "$ExtUtils::ParseXS::END:");
-    push(@{ $pxs->{line_no} }, $pxs->{line_no}->[-1]);
-
     $_ = '';
 
     # Check all the @{ $pxs->{line}} lines for balance: all the
@@ -1810,7 +1799,7 @@ sub parse {
     my $case_had_cond;       # the previous CASE had a condition
 
     # Repeatedly look for CASE or XSUB body.
-    while (@{ $pxs->{line} }) {
+    while (1) {
         # Parse a CASE statement if present.
         my ($case) =
             $self->parse_keywords(
@@ -1830,10 +1819,10 @@ sub parse {
         else {
             $seen_bare_xbody = 1;
             if ($num++) {
-                my $l = $pxs->{line}[0];
                 # After the first CASE+body, we should only encounter
                 # further CASE+bodies or end-of-paragraph
-                last if $l eq "$ExtUtils::ParseXS::END:";
+                last unless @{$pxs->{line}};
+                my $l = $pxs->{line}[0];
                 $pxs->death(
                     $l =~ /^$ExtUtils::ParseXS::BLOCK_regexp/o
                             ? "Error: misplaced '$1:'"
@@ -5701,8 +5690,7 @@ sub parse {
 
     $self->SUPER::parse($pxs); # set file/line_no/lines
     $xsub->{seen_PPCODE} = 1;
-    # The only thing left should be the special "!End!\n\n" token.
-    $pxs->death("Error: PPCODE must be the last thing") if @{$pxs->{line}} > 1;
+    $pxs->death("Error: PPCODE must be the last thing") if @{$pxs->{line}};
     1;
 }