[playground] Add Reset button (#17236)

## Summary

Add a *Reset* button to both Ruff's and Red Knot's playground that
resets the playground to its initial state.

Closes https://github.com/astral-sh/ruff/issues/17195

## Test Plan



https://github.com/user-attachments/assets/753cca19-155a-44b1-89ba-76744487a55d


https://github.com/user-attachments/assets/7d19f04c-70f4-4d9e-b745-0486cb1d4993

playground/knot/src/Editor/Chrome.tsx

@@ -40,15 +40,15 @@ export interface Props {
   theme: Theme;
   selectedFileName: string;
 
-  onFileAdded(workspace: Workspace, name: string): void;
+  onAddFile(workspace: Workspace, name: string): void;
 
-  onFileChanged(workspace: Workspace, content: string): void;
+  onChangeFile(workspace: Workspace, content: string): void;
 
-  onFileRenamed(workspace: Workspace, file: FileId, newName: string): void;
+  onRenameFile(workspace: Workspace, file: FileId, newName: string): void;
 
-  onFileRemoved(workspace: Workspace, file: FileId): void;
+  onRemoveFile(workspace: Workspace, file: FileId): void;
 
-  onFileSelected(id: FileId): void;
+  onSelectFile(id: FileId): void;
 }
 
 export default function Chrome({
@@ -56,11 +56,11 @@ export default function Chrome({
   selectedFileName,
   workspacePromise,
   theme,
-  onFileAdded,
-  onFileRenamed,
-  onFileRemoved,
-  onFileSelected,
-  onFileChanged,
+  onAddFile,
+  onRenameFile,
+  onRemoveFile,
+  onSelectFile,
+  onChangeFile,
 }: Props) {
   const workspace = use(workspacePromise);
 
@@ -74,7 +74,7 @@ export default function Chrome({
   } | null>(null);
 
   const handleFileRenamed = (file: FileId, newName: string) => {
-    onFileRenamed(workspace, file, newName);
+    onRenameFile(workspace, file, newName);
     editorRef.current?.editor.focus();
   };
 
@@ -129,9 +129,9 @@ export default function Chrome({
           ?.dispose();
       }
 
-      onFileRemoved(workspace, id);
+      onRemoveFile(workspace, id);
     },
-    [workspace, files.index, onFileRemoved],
+    [workspace, files.index, onRemoveFile],
   );
 
   const checkResult = useCheckResult(files, workspace, secondaryTool);
@@ -144,9 +144,9 @@ export default function Chrome({
             files={files.index}
             theme={theme}
             selected={files.selected}
-            onAdd={(name) => onFileAdded(workspace, name)}
+            onAdd={(name) => onAddFile(workspace, name)}
             onRename={handleFileRenamed}
-            onSelected={onFileSelected}
+            onSelect={onSelectFile}
             onRemove={handleRemoved}
           />
           <PanelGroup direction="horizontal" autoSaveId="main">
@@ -167,8 +167,8 @@ export default function Chrome({
                     diagnostics={checkResult.diagnostics}
                     workspace={workspace}
                     onMount={handleEditorMount}
-                    onChange={(content) => onFileChanged(workspace, content)}
-                    onFileOpened={onFileSelected}
+                    onChange={(content) => onChangeFile(workspace, content)}
+                    onOpenFile={onSelectFile}
                   />
                   {checkResult.error ? (
                     <div

playground/knot/src/Editor/Editor.tsx

@@ -38,7 +38,7 @@ type Props = {
   workspace: Workspace;
   onChange(content: string): void;
   onMount(editor: IStandaloneCodeEditor, monaco: Monaco): void;
-  onFileOpened(file: FileId): void;
+  onOpenFile(file: FileId): void;
 };
 
 export default function Editor({
@@ -51,7 +51,7 @@ export default function Editor({
   workspace,
   onChange,
   onMount,
-  onFileOpened,
+  onOpenFile,
 }: Props) {
   const serverRef = useRef<PlaygroundServer | null>(null);
 
@@ -59,7 +59,7 @@ export default function Editor({
     serverRef.current.update({
       files,
       workspace,
-      onFileOpened,
+      onOpenFile,
     });
   }
 
@@ -96,7 +96,7 @@ export default function Editor({
       const server = new PlaygroundServer(instance, {
         workspace,
         files,
-        onFileOpened,
+        onOpenFile,
       });
 
       server.updateDiagnostics(diagnostics);
@@ -105,11 +105,12 @@ export default function Editor({
       onMount(editor, instance);
     },
 
-    [files, onFileOpened, workspace, onMount, diagnostics],
+    [files, onOpenFile, workspace, onMount, diagnostics],
   );
 
   return (
     <Moncao
+      key={files.playgroundRevision}
       onMount={handleMount}
       options={{
         fixedOverflowWidgets: true,
@@ -133,7 +134,7 @@ export default function Editor({
 interface PlaygroundServerProps {
   workspace: Workspace;
   files: ReadonlyFiles;
-  onFileOpened: (file: FileId) => void;
+  onOpenFile: (file: FileId) => void;
 }
 
 class PlaygroundServer
@@ -333,7 +334,7 @@ class PlaygroundServer
     if (files.selected !== fileId) {
       source.setModel(model);
 
-      this.props.onFileOpened(fileId);
+      this.props.onOpenFile(fileId);
     }
 
     if (selectionOrPosition != null) {

playground/knot/src/Editor/Files.tsx

@@ -14,7 +14,7 @@ export interface Props {
 
   onRemove(id: FileId): void;
 
-  onSelected(id: FileId): void;
+  onSelect(id: FileId): void;
 
   onRename(id: FileId, newName: string): void;
 }
@@ -26,7 +26,7 @@ export function Files({
   onAdd,
   onRemove,
   onRename,
-  onSelected,
+  onSelect,
 }: Props) {
   const handleAdd = () => {
     let index: number | null = null;
@@ -54,7 +54,7 @@ export function Files({
           <FileEntry
             selected={selected === id}
             name={name}
-            onClicked={() => onSelected(id)}
+            onClicked={() => onSelect(id)}
             onRenamed={(newName) => {
               if (!files.some(({ name }) => name === newName)) {
                 onRename(id, newName);

playground/knot/src/Playground.tsx

@@ -1,4 +1,5 @@
 import {
+  ActionDispatch,
   Suspense,
   useCallback,
   useDeferredValue,
@@ -22,6 +23,7 @@ export default function Playground() {
   const [version, setVersion] = useState<string>("0.0.0");
   const [error, setError] = useState<string | null>(null);
   const workspacePromiseRef = useRef<Promise<Workspace> | null>(null);
+  const [workspace, setWorkspace] = useState<Workspace | null>(null);
 
   let workspacePromise = workspacePromiseRef.current;
   if (workspacePromise == null) {
@@ -29,43 +31,14 @@ export default function Playground() {
       (fetched) => {
         setVersion(fetched.version);
         const workspace = new Workspace("/", {});
-
-        let hasSettings = false;
-
-        for (const [name, content] of Object.entries(fetched.workspace.files)) {
-          let handle = null;
-          if (name === SETTINGS_FILE_NAME) {
-            updateOptions(workspace, content, setError);
-            hasSettings = true;
-          } else {
-            handle = workspace.openFile(name, content);
-          }
-
-          dispatchFiles({ type: "add", handle, content, name });
-        }
-
-        if (!hasSettings) {
-          updateOptions(workspace, null, setError);
-        }
-
-        dispatchFiles({
-          type: "selectFileByName",
-          name: fetched.workspace.current,
-        });
-
+        restoreWorkspace(workspace, fetched.workspace, dispatchFiles, setError);
+        setWorkspace(workspace);
         return workspace;
       },
     );
   }
 
-  const [files, dispatchFiles] = useReducer(filesReducer, {
-    index: [],
-    contents: Object.create(null),
-    handles: Object.create(null),
-    nextId: 0,
-    revision: 0,
-    selected: null,
-  });
+  const [files, dispatchFiles] = useReducer(filesReducer, INIT_FILES_STATE);
 
   const fileName = useMemo(() => {
     return (
@@ -155,6 +128,29 @@ export default function Playground() {
     dispatchFiles({ type: "selectFile", id: file });
   }, []);
 
+  const handleReset = useCallback(() => {
+    if (workspace == null) {
+      return;
+    }
+
+    // Close all open files
+    for (const file of files.index) {
+      const handle = files.handles[file.id];
+
+      if (handle != null) {
+        try {
+          workspace.closeFile(handle);
+        } catch (e) {
+          setError(formatError(e));
+        }
+      }
+    }
+
+    dispatchFiles({ type: "reset" });
+
+    restoreWorkspace(workspace, DEFAULT_WORKSPACE, dispatchFiles, setError);
+  }, [files.handles, files.index, workspace]);
+
   return (
     <main className="flex flex-col h-full bg-ayu-background dark:bg-ayu-background-dark">
       <Header
@@ -164,6 +160,7 @@ export default function Playground() {
         version={version}
         onChangeTheme={setTheme}
         onShare={handleShare}
+        onReset={workspace == null ? undefined : handleReset}
       />
 
       <Suspense fallback={<Loading />}>
@@ -172,11 +169,11 @@ export default function Playground() {
           workspacePromise={workspacePromise}
           theme={theme}
           selectedFileName={fileName}
-          onFileAdded={handleFileAdded}
-          onFileRenamed={handleFileRenamed}
-          onFileRemoved={handleFileRemoved}
-          onFileSelected={handleFileSelected}
-          onFileChanged={handleFileChanged}
+          onAddFile={handleFileAdded}
+          onRenameFile={handleFileRenamed}
+          onRemoveFile={handleFileRemoved}
+          onSelectFile={handleFileSelected}
+          onChangeFile={handleFileChanged}
         />
       </Suspense>
       {error ? (
@@ -208,6 +205,14 @@ export const DEFAULT_SETTINGS = JSON.stringify(
   4,
 );
 
+const DEFAULT_WORKSPACE = {
+  files: {
+    "main.py": "import os",
+    "knot.json": DEFAULT_SETTINGS,
+  },
+  current: "main.py",
+};
+
 /**
  * Persists the files to local storage. This is done deferred to avoid too frequent writes.
  */
@@ -254,6 +259,13 @@ interface FilesState {
    * The revision. Gets incremented every time files changes.
    */
   revision: number;
+
+  /**
+   * Revision identifying this playground. Gets incremented every time the
+   * playground is reset.
+   */
+  playgroundRevision: number;
+
   nextId: FileId;
 }
 
@@ -276,7 +288,18 @@ export type FileAction =
       id: FileId;
     }
   | { type: "selectFile"; id: FileId }
-  | { type: "selectFileByName"; name: string };
+  | { type: "selectFileByName"; name: string }
+  | { type: "reset" };
+
+const INIT_FILES_STATE: ReadonlyFiles = {
+  index: [],
+  contents: Object.create(null),
+  handles: Object.create(null),
+  nextId: 0,
+  revision: 0,
+  selected: null,
+  playgroundRevision: 0,
+};
 
 function filesReducer(
   state: Readonly<FilesState>,
@@ -366,6 +389,14 @@ function filesReducer(
         selected,
       };
     }
+
+    case "reset": {
+      return {
+        ...INIT_FILES_STATE,
+        playgroundRevision: state.playgroundRevision + 1,
+        revision: state.revision + 1,
+      };
+    }
   }
 }
 
@@ -410,13 +441,7 @@ async function startPlayground(): Promise<InitializedPlayground> {
 
   const restored = await restore();
 
-  const workspace = restored ?? {
-    files: {
-      "main.py": "import os",
-      "knot.json": DEFAULT_SETTINGS,
-    },
-    current: "main.py",
-  };
+  const workspace = restored ?? DEFAULT_WORKSPACE;
 
   return {
     version: "0.0.0",
@@ -457,3 +482,36 @@ function updateFile(
 function Loading() {
   return <div className="align-middle  text-center my-2">Loading...</div>;
 }
+
+function restoreWorkspace(
+  workspace: Workspace,
+  state: {
+    files: { [name: string]: string };
+    current: string;
+  },
+  dispatchFiles: ActionDispatch<[FileAction]>,
+  setError: (error: string | null) => void,
+) {
+  let hasSettings = false;
+
+  for (const [name, content] of Object.entries(state.files)) {
+    let handle = null;
+    if (name === SETTINGS_FILE_NAME) {
+      updateOptions(workspace, content, setError);
+      hasSettings = true;
+    } else {
+      handle = workspace.openFile(name, content);
+    }
+
+    dispatchFiles({ type: "add", handle, content, name });
+  }
+
+  if (!hasSettings) {
+    updateOptions(workspace, null, setError);
+  }
+
+  dispatchFiles({
+    type: "selectFileByName",
+    name: state.current,
+  });
+}

playground/ruff/src/Editor/Chrome.tsx

@@ -65,6 +65,15 @@ export default function Chrome() {
     [pythonSource],
   );
 
+  const handleResetClicked = useCallback(() => {
+    const pythonSource = DEFAULT_PYTHON_SOURCE;
+    const settings = stringify(Workspace.defaultSettings());
+
+    persistLocal({ pythonSource, settingsSource: settings });
+    setPythonSource(pythonSource);
+    setSettings(settings);
+  }, []);
+
   const source: Source | null = useMemo(() => {
     if (pythonSource == null || settings == null) {
       return null;
@@ -82,6 +91,7 @@ export default function Chrome() {
         version={ruffVersion}
         onChangeTheme={setTheme}
         onShare={handleShare}
+        onReset={handleResetClicked}
       />
 
       <div className="flex grow">

playground/shared/src/Header.tsx

@@ -4,6 +4,7 @@ import ThemeButton from "./ThemeButton";
 import ShareButton from "./ShareButton";
 import { Theme } from "./theme";
 import VersionTag from "./VersionTag";
+import AstralButton from "./AstralButton";
 
 export default function Header({
   edit,
@@ -11,6 +12,7 @@ export default function Header({
   logo,
   version,
   onChangeTheme,
+  onReset,
   onShare,
 }: {
   edit: number | null;
@@ -18,43 +20,42 @@ export default function Header({
   logo: "ruff" | "astral";
   version: string | null;
   onChangeTheme: (theme: Theme) => void;
-  onShare?: () => void;
+  onReset?(): void;
+  onShare: () => void;
 }) {
   return (
     <div
-      className={classNames(
-        "w-full",
-        "flex",
-        "justify-between",
-        "pl-5",
-        "sm:pl-1",
-        "pr-4",
-        "lg:pr-6",
-        "z-10",
-        "top-0",
-        "left-0",
-        "-mb-px",
-        "antialiased",
-        "border-b",
-        "border-gray-200",
-        "dark:border-b-radiate",
-        "dark:bg-galaxy",
-      )}
+      className="
+        w-full
+        flex
+        justify-between
+        antialiased
+        border-b
+        border-gray-200
+        dark:border-b-radiate
+        dark:bg-galaxy
+      "
     >
       <div className="py-4 pl-2">
         <Logo name={logo} className="fill-galaxy dark:fill-radiate" />
       </div>
-      <div className="flex items-center min-w-0">
+      <div className="flex items-center min-w-0 gap-4 mx-2">
         {version ? (
-          <div className="hidden sm:flex items-center">
+          <div className="hidden sm:flex">
             <VersionTag>v{version}</VersionTag>
           </div>
         ) : null}
         <Divider />
         <RepoButton />
         <Divider />
+        <div className="max-sm:hidden flex">
+          <ResetButton onClicked={onReset} />
+        </div>
+        <div className="max-sm:hidden flex">
           <ShareButton key={edit} onShare={onShare} />
+        </div>
         <Divider />
+
         <ThemeButton theme={theme} onChange={onChangeTheme} />
       </div>
     </div>
@@ -63,7 +64,16 @@ export default function Header({
 
 function Divider() {
   return (
-    <div className="hidden sm:block mx-6 lg:mx-4 w-px h-8 bg-gray-200 dark:bg-gray-700" />
+    <div
+      className={classNames(
+        "max-sm:hidden",
+        "visible",
+        "w-px",
+        "h-8",
+        "bg-gray-200",
+        "dark:bg-gray-700",
+      )}
+    />
   );
 }
 
@@ -121,3 +131,16 @@ function Logo({
       );
   }
 }
+
+function ResetButton({ onClicked }: { onClicked?: () => void }) {
+  return (
+    <AstralButton
+      type="button"
+      className="relative flex-none leading-6 py-1.5 px-3 shadow-xs disabled:opacity-50"
+      disabled={onClicked == null}
+      onClick={onClicked}
+    >
+      Reset
+    </AstralButton>
+  );
+}

playground/shared/src/ShareButton.tsx

@@ -1,7 +1,7 @@
 import { useEffect, useState } from "react";
 import AstralButton from "./AstralButton";
 
-export default function ShareButton({ onShare }: { onShare?: () => void }) {
+export default function ShareButton({ onShare }: { onShare: () => void }) {
   const [copied, setCopied] = useState(false);
 
   useEffect(() => {
@@ -28,15 +28,11 @@ export default function ShareButton({ onShare }: { onShare?: () => void }) {
     <AstralButton
       type="button"
       className="relative flex-none leading-6 py-1.5 px-3 shadow-xs disabled:opacity-50"
-      disabled={!onShare || copied}
-      onClick={
-        onShare
-          ? () => {
+      disabled={copied}
+      onClick={() => {
         setCopied(true);
         onShare();
-            }
-          : undefined
-      }
+      }}
     >
       <span
         className="absolute inset-0 flex items-center justify-center"

playground/shared/src/ThemeButton.tsx

@@ -14,7 +14,7 @@ export default function ThemeButton({
   return (
     <AstralButton
       type="button"
-      className="ml-4 sm:ml-0 dark:shadow-copied"
+      className="sm:ml-0 dark:shadow-copied"
       onClick={() => onChange(theme === "light" ? "dark" : "light")}
     >
       <span className="sr-only">