Fix: Shift+Click+Drag from outputs with Subgraph outputs (#5115)

* fix: Handle shift+click+drag to collectively move outputs when connected to a subgraph output

* [Bug]: Multiple issues with shift-dragging links to subgraph output node input slots
Fixes #4877
When shift clicking, ignore links that are no longer present in the subgraph.

* cleanup: Utility function to filter for relevant outputs when shift+clicking

* cleanup: Remove some pieces that are redundant in this context.
Different enough to warrant not extracting a common function yet.

src/lib/litegraph/src/LGraphCanvas.ts

@@ -36,6 +36,7 @@ import type {
   INodeSlot,
   INodeSlotContextItem,
   ISlotType,
+  LinkNetwork,
   LinkSegment,
   NullableProperties,
   Point,
@@ -2575,16 +2576,27 @@ export class LGraphCanvas
     } else if (!node.flags.collapsed) {
       const { inputs, outputs } = node
 
+      function hasRelevantOutputLinks(
+        output: INodeOutputSlot,
+        network: LinkNetwork
+      ): boolean {
+        const outputLinks = [
+          ...(output.links ?? []),
+          ...[...(output._floatingLinks ?? new Set())]
+        ]
+        return outputLinks.some(
+          (linkId) =>
+            typeof linkId === 'number' && network.getLink(linkId) !== undefined
+        )
+      }
+
       // Outputs
       if (outputs) {
         for (const [i, output] of outputs.entries()) {
           const link_pos = node.getOutputPos(i)
           if (isInRectangle(x, y, link_pos[0] - 15, link_pos[1] - 10, 30, 20)) {
             // Drag multiple output links
-            if (
-              e.shiftKey &&
-              (output.links?.length || output._floatingLinks?.size)
-            ) {
+            if (e.shiftKey && hasRelevantOutputLinks(output, graph)) {
               linkConnector.moveOutputLink(graph, output)
               this.#linkConnectorDrop()
               return

src/lib/litegraph/src/canvas/LinkConnector.ts

@@ -314,6 +314,27 @@ export class LinkConnector {
         this.outputLinks.push(link)
 
         try {
+          if (link.target_id === SUBGRAPH_OUTPUT_ID) {
+            if (!(network instanceof Subgraph)) {
+              console.warn(
+                'Subgraph output link found in non-subgraph network.'
+              )
+              continue
+            }
+
+            const output = network.outputs.at(link.target_slot)
+            if (!output) throw new Error('No subgraph output found for link.')
+
+            const renderLink = new ToOutputFromIoNodeLink(
+              network,
+              network.outputNode,
+              output
+            )
+            renderLink.fromDirection = LinkDirection.NONE
+            renderLinks.push(renderLink)
+
+            continue
+          }
           const renderLink = new MovingOutputLink(
             network,
             link,