Add path closing and segment extension to the Pen tool (#753)

* Close paths with pen tool

* Issue Z command always at end of path

* Small code review style changes

* Extending paths

* Fix mirror on extend path

* Code review tweaks

Co-authored-by: Keavon Chambers <keavon@keavon.com>

graphene/src/layers/id_vec.rs

@@ -34,7 +34,7 @@ impl<T> IdBackedVec<T> {
 		Some(self.next_id)
 	}
 
-	// Push an element to the end of the vector
+	/// Push an element to the end of the vector
 	pub fn push_end(&mut self, element: T) -> Option<ElementId> {
 		self.next_id += 1;
 		self.elements.push(element);
@@ -113,7 +113,7 @@ impl<T> IdBackedVec<T> {
 	}
 
 	/// Enumerate the ids and elements in this container `(&ElementId, &T)`
-	pub fn enumerate(&self) -> impl Iterator<Item = (&ElementId, &T)> {
+	pub fn enumerate(&self) -> std::iter::Zip<core::slice::Iter<u64>, core::slice::Iter<T>> {
 		self.element_ids.iter().zip(self.elements.iter())
 	}
 

graphene/src/layers/vector/subpath.rs

@@ -384,18 +384,21 @@ impl Subpath {
 				} else if last_out_handle.is_some() || first_in_handle.is_some() {
 					result.push('Q');
 					write_positions(&mut result, [last_out_handle, first_in_handle, first_in_anchor]);
-				} else {
-					result.push('Z');
 				}
-			} else if command == 'M' {
-				// Update the last moveto position
+				result.push('Z');
+			}
+			// Update the last moveto position
+			else if command == 'M' {
 				(first_in_handle, first_in_anchor) = (in_handle, anchor);
 				result.push(command);
 				write_positions(&mut result, [None, None, anchor]);
-			} else {
+			}
+			// Write other path commands (line to/quadratic to/cubic to)
+			else {
 				result.push(command);
 				write_positions(&mut result, [last_out_handle, in_handle, anchor]);
 			}
+
 			start_new_contour = command == 'Z';
 			last_out_handle = out_handle;
 		}