Add Layer::GetFeatureCount method

lib/Geo/GDAL/FFI/Layer.pm

@@ -86,6 +86,11 @@ sub GetFeature {
     return bless \$f, 'Geo::GDAL::FFI::Feature';
 }
 
+sub GetFeatureCount {
+    my ($self, $force) = @_;
+    Geo::GDAL::FFI::OGR_L_GetFeatureCount($$self, !!$force);
+}
+
 sub SetFeature {
     my ($self, $f) = @_;
     Geo::GDAL::FFI::OGR_L_SetFeature($$self, $$f);
@@ -175,6 +180,13 @@ A set of (vector) features having a same schema (the same Defn
 object). Obtain a layer object by the CreateLayer or GetLayer method
 of a vector dataset object.
 
+Note that the system stores a reference to the parent dataset for
+each layer object to ensure layer objects remain viable.
+If you are relying on a dataset object's destruction to
+flush its dataset cache and then close it then you need to ensure
+all associated child layers are also destroyed.  Failure to do so could
+lead to corrupt data when reading in newly written files.
+
 =head1 METHODS
 
 =head2 GetDefn
@@ -206,6 +218,10 @@ Returns the FeatureDefn object for this layer.
 =head2 DeleteFeature
 
  $layer->DeleteFeature($fid);
+
+=head2 GetFeatureCount
+
+ my $count = $layer->GetFeatureCount();
 
 =head2 GetExtent
  $layer->GetExtent();

t/00.t

@@ -296,6 +296,7 @@ if(1){
     my $d = $l->GetDefn();
     my $f = Geo::GDAL::FFI::Feature->new($d);
     $l->CreateFeature($f);
+    undef $l; #  otherwise $ds is not flushed due to parent ref
     $ds = Open('test.shp');
     $l = $ds->GetLayer;
     $d = $l->GetDefn();

t/layer.t

@@ -34,6 +34,13 @@ $f->SetGeomField([WKT => 'POLYGON ((2 1, 2 2, 4 2, 4 1, 2 1))']);
 
 $method->CreateFeature($f);
 
+{
+    my $feature_count = $layer->GetFeatureCount;
+    is $feature_count, 1, 'Got correct feature count';
+    $feature_count = $layer->GetFeatureCount (1);
+    is $feature_count, 1, 'Got correct feature count with force arg=true';
+}
+
 my $progress;
 
 my $result;
@@ -136,7 +143,7 @@ is_deeply $layer->GetExtent(1), $exp_extent, 'Got correct layer extent when forc
     {
         #local $TODO = 'sql DISTINCT not yet working, despite following GDAL doc example';
         is_deeply (\@items, ['one','ten'], 'got correct distinct items');
-    }    
+    }
 
     my $result = eval {
         $ds->ExecuteSQL (qq{CREATE SPATIAL INDEX ON "$layer_name"});