[diffs/edit] add folding support

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

@@ -1053,10 +1053,12 @@ const file: FileContents | undefined = editor.getFile();
 // Full document text, or '' when nothing is attached.
 const text: string = editor.getText();
 
-// Snapshot selections and scroll position for persistence or remount restore.
+// Snapshot selections, active folds, and scroll position for persistence or
+// remount restore.
 const state: EditorState = editor.getState();
 // EditorState = {
 //   selections?: EditorSelection[];
+//   foldRanges?: LineRange[]; // zero-based; standalone closers stay visible
 //   view?: { scrollLeft: number; scrollTop: number };
 // }
 

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();
@@ -373,6 +402,7 @@ export class File<
       this.workerManager = undefined;
       this.file = undefined;
     }
+    this.foldRanges = [];
 
     this.enabled = false;