Pass isSourceHandle flag to onEdgeUpdateStart

- This allows to know during an edge update which side of the edge is getting dragged by the user.
- Use cases include showing custom validation hints to the user during an edge update, e.g. which handles can be connected to and which not. This would otherwise not be possible without knowing which side is updated.

src/components/Edges/wrapEdge.tsx

@@ -140,7 +140,7 @@ export default (EdgeComponent: ComponentType<EdgeProps>) => {
         const isValidConnection = () => true;
         const isTarget = isSourceHandle;
 
-        onEdgeUpdateStart?.(event, edgeElement);
+        onEdgeUpdateStart?.(event, edgeElement, isSourceHandle);
 
         const _onEdgeUpdate = onEdgeUpdateEnd
           ? (evt: MouseEvent): void => onEdgeUpdateEnd(evt, edgeElement)

src/container/EdgeRenderer/index.tsx

@@ -34,7 +34,7 @@ interface EdgeRendererProps {
   onEdgeMouseEnter?: (event: React.MouseEvent, edge: Edge) => void;
   onEdgeMouseMove?: (event: React.MouseEvent, edge: Edge) => void;
   onEdgeMouseLeave?: (event: React.MouseEvent, edge: Edge) => void;
-  onEdgeUpdateStart?: (event: React.MouseEvent, edge: Edge) => void;
+  onEdgeUpdateStart?: (event: React.MouseEvent, edge: Edge, isSourceHandle: boolean) => void;
   onEdgeUpdateEnd?: (event: MouseEvent, edge: Edge) => void;
   edgeUpdaterRadius?: number;
 }

src/container/ReactFlow/index.tsx

@@ -123,7 +123,7 @@ export interface ReactFlowProps extends Omit<HTMLAttributes<HTMLDivElement>, 'on
   onEdgeMouseMove?: (event: ReactMouseEvent, edge: Edge) => void;
   onEdgeMouseLeave?: (event: ReactMouseEvent, edge: Edge) => void;
   onEdgeDoubleClick?: (event: ReactMouseEvent, edge: Edge) => void;
-  onEdgeUpdateStart?: (event: ReactMouseEvent, edge: Edge) => void;
+  onEdgeUpdateStart?: (event: ReactMouseEvent, edge: Edge, isSourceHandle: boolean) => void;
   onEdgeUpdateEnd?: (event: MouseEvent, edge: Edge) => void;
   edgeUpdaterRadius?: number;
   nodeTypesId?: string;

src/types/index.ts

@@ -132,7 +132,7 @@ export interface WrapEdgeProps<T = any> {
   onMouseMove?: (event: React.MouseEvent, edge: Edge) => void;
   onMouseLeave?: (event: React.MouseEvent, edge: Edge) => void;
   edgeUpdaterRadius?: number;
-  onEdgeUpdateStart?: (event: React.MouseEvent, edge: Edge) => void;
+  onEdgeUpdateStart?: (event: React.MouseEvent, edge: Edge, isSourceHandle: boolean) => void;
   onEdgeUpdateEnd?: (event: MouseEvent, edge: Edge) => void;
 }