Handle 'unknown' op in DBD::SQLite::VirtualTable::PerlData

This patch adds code and a test when SQLite generates an 'unknown'
op for a table join in the BEST_INDEX() callback. The Perl code crashed
when such an op was generated for a JOIN criterion by the SQLite engine.

The SQLite engine creates an 'unknown' op on the following SQL
for example:

                select r.nodepath
                  from temp.scan_results r
                       left join temp.scan_results m
                             on r.nodepath = m.nodepath+1
                 where m.nodepath is null

The important part is that the right side of the left join must be
checked for IS NULL.

MANIFEST

@@ -138,6 +138,7 @@ t/virtual_table/20_perldata.t
 t/virtual_table/21_perldata_charinfo.t
 t/virtual_table/rt_124941.t
 t/virtual_table/rt_99748.t
+t/virtual_table/unknown_op.t
 typemap
 xt/cpp_comments.t
 xt/meta.t

lib/DBD/SQLite/VirtualTable/PerlData.pm

@@ -88,7 +88,7 @@ sub BEST_INDEX {
   # in FILTER() for deciding which rows match the constraints.
   my @conditions;
   my $ix = 0;
-  foreach my $constraint (grep {$_->{usable}} @$constraints) {
+  foreach my $constraint (grep {$_->{usable} and exists $SQLOP2PERLOP{ $_->{op} } } @$constraints) {
     my $col = $constraint->{col};
     my ($member, $optype);
 

t/virtual_table/unknown_op.t

@@ -0,0 +1,93 @@
+#!perl -w
+
+use strict;
+use Test::More tests => 4;
+
+our $scan_results = [
+    { nodepath => 1 },
+    { nodepath => 2 },
+    { nodepath => 3 },
+];
+
+my $dbh = DBI->connect("dbi:SQLite:dbname=:memory:", '', '',
+                        {RaiseError => 1, AutoCommit => 1});
+
+# register the module
+$dbh->sqlite_create_module(perl => "DBD::SQLite::VirtualTable::PerlData");
+$dbh->do(<<'SQL');
+        CREATE VIRTUAL TABLE temp.scan_results
+        USING perl(file varchar,
+                             value varchar,
+                             selector varchar,
+                             nodepath varchar,
+                             expected integer,
+                             preference integer,
+                             complexity integer,
+                             location varchar,
+                             type     varchar,
+                             hashrefs="main::scan_results")
+SQL
+
+my $ok = eval {
+    my $sth = $dbh->prepare(<<'SQL');
+                select distinct r.selector
+                  from temp.scan_results r
+                       left join temp.scan_results m
+                             on r.nodepath = m.nodepath+1
+                 where m.nodepath = 1
+SQL
+$sth->execute;
+    #use DBIx::RunSQL; print DBIx::RunSQL->format_results( sth => $sth );
+    1;
+};
+is $ok, 1, "We survive a numeric comparison";
+undef $ok;
+
+$ok = eval {
+    my $sth = $dbh->prepare(<<'SQL');
+                select distinct r.selector
+                  from temp.scan_results r
+                       left join temp.scan_results m
+                             on r.nodepath = m.nodepath+1
+                 where m.nodepath is not null
+SQL
+    $sth->execute;
+    1;
+    #use DBIx::RunSQL; print DBIx::RunSQL->format_results( sth => $sth );
+};
+is $ok, 1, "We survive an isnull comparison";
+undef $ok;
+
+$ok = eval {
+    my $sth = $dbh->prepare(<<'SQL');
+                select r.nodepath
+                  from temp.scan_results r
+                       left join temp.scan_results m
+                             on r.nodepath = m.nodepath+1
+                 where r.nodepath is null
+SQL
+    $sth->execute;
+    1;
+    #use DBIx::RunSQL; print DBIx::RunSQL->format_results( sth => $sth );
+};
+is $ok, 1, "We survive an isnull comparison on the left side";
+undef $ok;
+
+my $sth;
+$ok = eval {
+    $sth = $dbh->prepare(<<'SQL');
+                select r.nodepath
+                  from temp.scan_results r
+                       left join temp.scan_results m
+                             on r.nodepath = m.nodepath+1
+                 where m.nodepath is null
+SQL
+    $sth->execute;
+    1;
+    #use DBIx::RunSQL; print DBIx::RunSQL->format_results( sth => $sth );
+};
+is $ok, 1, "We survive an isnull comparison on the right side";
+undef $ok;
+#my $rows = $sth->fetchall_arrayref;
+#use Data::Dumper;
+#warn Dumper $rows;