feat(python): support Ruff formatting and config directories (#1573)

Ruff is now an external formatter for Python next to the Ruff language server: Settings › Languages & Frameworks › Ruff has the executable path, a configuration directory (or file), the provider preference, enabled languages, run-on-save, and Reformat with Ruff. Formatting runs on the unsaved document through stdin (with Ruff's --range for selections, in 1-based code-point columns) and never writes the file first. The configuration directory is shared with Ruff LSP, which can then start without a root marker. Tools that can't format a language are rejected even when requested.

Co-authored-by: muutot <[email protected]>
Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/features/tools/__tests__/tools.test.tsx

@@ -147,6 +147,25 @@ describe("missing language server prompt", () => {
     off();
   });
 
+  it("offers Ruff formatting even when another Python server is installed", async () => {
+    const installed = sampleTools().find((t) => t.name === "basedpyright")!;
+    backend.tools.push({
+      ...installed,
+      name: "ruff",
+      displayName: "Ruff",
+      command: "ruff",
+      installMethod: "uv (virtualenv)",
+      languages: ["Python"],
+      alternatives: [],
+    });
+    await promptInstall("ruff", true, new Set(), true);
+    expect(notes.at(-1)).toMatchObject({
+      title: "Ruff is not installed",
+      body: "Reformat Code needs Ruff. Install it via uv (virtualenv)?",
+      key: missingKey("ruff"),
+    });
+  });
+
   it("stays silent when an installed alternative serves the same languages", async () => {
     const off = installMissingServerPrompts();
     // typescript-language-server (on PATH) covers vtsls' languages.

src/features/tools/index.ts

@@ -46,7 +46,12 @@ export function activate(): () => void {
         hidden: true,
         run: async ({ arg }) => {
           if (arg && typeof arg === "object" && "name" in arg && typeof arg.name === "string") {
-            await promptInstall(arg.name, !("sticky" in arg) || arg.sticky !== false);
+            await promptInstall(
+              arg.name,
+              !("sticky" in arg) || arg.sticky !== false,
+              new Set(),
+              "formatter" in arg && arg.formatter === true,
+            );
           }
         },
       },

src/features/tools/missing.ts

@@ -21,12 +21,14 @@ export async function promptInstall(
   name: string,
   sticky = true,
   offered: ReadonlySet<string> = new Set(),
+  formatter = false,
 ): Promise<boolean> {
   if (!useTools.getState().loaded) await refreshTools();
   const tool = toolByName(name);
   if (!tool || !tool.canInstall || tool.status !== "missing") return false;
   const position = tool.alternatives.indexOf(name);
   if (position > 0 && tool.alternatives.slice(0, position).some((n) => offered.has(n))) return false;
+  formatter ||= tool.kind === "formatter";
   // An installed alternative (typescript-language-server for vtsls) already serves these files.
   const served = useTools
     .getState()
@@ -37,17 +39,16 @@ export async function promptInstall(
         t.status !== "missing" &&
         t.languages.some((l) => tool.languages.includes(l)),
     );
-  if (tool.kind !== "formatter" && served) return false;
+  if (!formatter && served) return false;
   const key = missingKey(name);
   const langs = tool.languages.length ? tool.languages.join(", ") : "these files";
   notifications().notify({
     group: "tools",
     level: "warning",
     title: tx`${tool.displayName} is not installed`,
-    body:
-      tool.kind === "formatter"
-        ? tx`Reformat Code needs ${tool.displayName}. Install it via ${tool.installMethod}?`
-        : tx`Code insight for ${langs} needs ${tool.command}. Install it via ${tool.installMethod}?`,
+    body: formatter
+      ? tx`Reformat Code needs ${tool.displayName}. Install it via ${tool.installMethod}?`
+      : tx`Code insight for ${langs} needs ${tool.command}. Install it via ${tool.installMethod}?`,
     key,
     sticky,
     actions: [