t/porting/podcheck.t - some verbatim text is copied from the source

So we should check if it is still in sync with the source, and ignore
any line length issues as the source needs to be changed, not the copy.

To enable this simply put "file source: FILENAME" or
"copied from: FILENAME" in the first line of the verbatim text.

t/porting/podcheck.t

@@ -1122,19 +1122,68 @@ package My::Pod::Checker {      # Extend Pod::Checker
 
         my $indent = $self->get_current_indent;
 
-        # Look at each line to verify it is short enough
+        # split the code by line.
         my @lines = split /^/, $running_simple_text{$addr};
-        for my $i (0 .. @lines - 1) {
-            $lines[$i] =~ s/\s+$//;
-            my $exceeds = length(Text::Tabs::expand($lines[$i]))
-                        + $indent - $MAX_LINE_LENGTH;
-            next unless $exceeds > 0;
-
-            $self->poderror({ -line => $start_line{$addr} + $i,
-                -msg => $line_length,
-                parameter => "+$exceeds (including " . ($indent - $INDENT) .
-                             " from =over's and $INDENT as base indent)",
-            });
+
+        # We have two cases here. The verbatim text may be copied from
+        # one of our files, in which case we check to make sure that the
+        # code in the documentation matches that of the code in the
+        # file, OR, we check the line lengths are appropriate. Copied text
+        # is identified by the first line containing one of the following
+        # strings: "file source: FILENAME" or "copied from: FILENAME" where
+        # the FILENAME actually exists.
+        #
+        # Yes, this implies that where we are copying code verbatim from
+        # one of our source files we do not check its length. This is
+        # because it is a copy, and we shouldn't require the code to be
+        # munged to be placed in the docs. This should only be used in
+        # pod files which are used to document the internals for other
+        # developers, as it may result in unpleasant to view HTML docs.
+
+        my $copied = 0;
+        if ($lines[0] =~ /(?:file source|copied from):\s*([\/\w.]+)/i and -e $1) {
+            # this text was copied from a source file. Make sure that it still
+            # matches the source. This is a whitespace insensitive match.
+
+            my $file = $1;
+            $copied = 1;
+            my $pat = "";
+            foreach my $line (@lines[1..$#lines]) {
+                # convert each line into a pattern fragment
+                $line =~ s/(?:(\s+)|(\S+))/$1 ? "\\s++" : quotemeta($2)/ge;
+                $pat .= $line;
+            }
+            # merge adjacent \s+ sequences
+            $pat =~ s/(?:\\s\+\+){2,}/\\s++/g;
+            # slurp the file
+            my $slurped = do {
+                open my $ifh, "<", $file
+                    or die "Failed to open '$file' for read: $!";
+                local $/;
+                <$ifh>;
+            };
+            if ($slurped !~ /$pat/) {
+                $self->poderror({ -line => $start_line{$addr},
+                    -msg => "Copied verbatim text is out of sync with source file",
+                    parameter => $file,
+                });
+            }
+        }
+        if (!$copied) {
+            # if the verbatim text has not been copied from one of our
+            # source files we look at each line to verify it is short enough
+            for my $i (0 .. @lines - 1) {
+                $lines[$i] =~ s/\s+$//;
+                my $exceeds = length(Text::Tabs::expand($lines[$i]))
+                            + $indent - $MAX_LINE_LENGTH;
+                next unless $exceeds > 0;
+
+                $self->poderror({ -line => $start_line{$addr} + $i,
+                    -msg => $line_length,
+                    parameter => "+$exceeds (including " . ($indent - $INDENT) .
+                                 " from =over's and $INDENT as base indent)",
+                });
+            }
         }
 
         undef $running_simple_text{$addr};