[diffs] add folding support

apps/docs/app/(diffs)/docs/Edit/constants.ts

@@ -1092,14 +1092,16 @@ const file: FileContents | undefined = editor.getFile();
 // Full document text, or '' when nothing is attached.
 const text: string = editor.getText();
 
-// Snapshot selections and horizontal code position for explicit restoration.
+// Snapshot selections, active folds, and horizontal code position for
+// persistence or remount restore.
 const state: EditorState = editor.getState();
 // EditorState = {
 //   selections?: EditorSelection[];
-//   view?: { scrollLeft: number };
+//   foldRanges?: LineRange[]; // zero-based; standalone closers stay visible
+//   view?: { scrollLeft: number; scrollTop: number };
 // }
 
-// Restore selections and horizontal code position after re-rendering.
+// Restore selections, folds, and horizontal code position after re-rendering.
 editor.setState(state);
 
 // Replace all cursors and ranges programmatically. Positions are zero-based;

packages/diffs/src/components/File.ts

@@ -33,6 +33,7 @@ import type {
   FileContents,
   HighlightedToken,
   LineAnnotation,
+  LineRange,
   PostRenderPhase,
   PrePropertiesConfig,
   RenderFileMetadata,
@@ -176,6 +177,7 @@ export class File<
   public file: FileContents | undefined;
   protected renderRange: RenderRange | undefined;
   protected enabled = true;
+  protected foldRanges: LineRange[] = [];
 
   protected editor: DiffsEditor<LAnnotation> | undefined;
 
@@ -214,6 +216,33 @@ export class File<
     return this.file;
   }
 
+  public __setFoldRanges(ranges: LineRange[]): void {
+    if (!this.updateFoldRanges(ranges)) {
+      return;
+    }
+    if (this.enabled && this.file != null) {
+      this.rerender();
+    }
+  }
+
+  protected updateFoldRanges(ranges: LineRange[]): boolean {
+    if (
+      ranges.length === this.foldRanges.length &&
+      ranges.every((range, index) => {
+        const previous = this.foldRanges[index];
+        return (
+          previous?.startLine === range.startLine &&
+          previous.endLine === range.endLine
+        );
+      })
+    ) {
+      return false;
+    }
+    this.foldRanges = ranges.map((range) => ({ ...range }));
+    this.fileRenderer.setFoldRanges(this.foldRanges);
+    return true;
+  }
+
   public onThemeChange(): void {
     this.fileRenderer.clearRenderCache();
     this.rerender();
@@ -391,6 +420,8 @@ export class File<
       this.workerManager = undefined;
       this.file = undefined;
     }
+    this.foldRanges = [];
+
     this.enabled = false;
   }