feat(python): add Pyrefly language server (#911)

Pyrefly (`pyrefly lsp`) joins basedpyright, Pyright and ty as a fallback Python language server. It is installable from Tools as a managed virtualenv tool and is listed among the interchangeable type checkers, before Ruff, so Ruff still runs after them.

Pyrefly only reports type errors in projects with a Pyrefly configuration (`pyrefly.toml` or `[tool.pyrefly]`); hover, completion and navigation work without one. A real-server test (ignored by default, needs `pyrefly` on PATH) covers startup, go-to-definition and diagnostics.

Co-authored-by: pcastro93 <[email protected]>

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

@@ -89,7 +89,7 @@ describe("Language Servers page settings", () => {
     const ty = details("ty (Python)");
     expect(within(ty).getByRole("button", { name: "Language server for Python" })).toHaveTextContent("Automatic");
     // The language is in the label already, so names drop a "(Python)" suffix.
-    expect(within(ty).getByText(/basedpyright → Pyright → ty\.$/)).toBeInTheDocument();
+    expect(within(ty).getByText(/basedpyright → Pyright → ty → Pyrefly\.$/)).toBeInTheDocument();
     await user.click(listItem("gopls")!);
     expect(within(details("gopls")).getByRole("checkbox", { name: /Use gopls/ })).toBeInTheDocument();
     expect(within(details("gopls")).queryByRole("button", { name: /^Language server for/ })).toBeNull();
@@ -108,7 +108,7 @@ describe("Language Servers page settings", () => {
     expect(picker).toHaveTextContent("ty");
     await user.click(picker);
     await user.click(screen.getByRole("option", { name: /Automatic/ }));
-    for (const name of ["basedpyright", "pyright", "ty"]) {
+    for (const name of ["basedpyright", "pyright", "ty", "pyrefly"]) {
       expect(stagedFor(`languageServers.${name}.enabled`)).toBeNull();
       expect(useTestForm.getState().values).not.toHaveProperty(`languageServers.${name}.enabled`);
     }
@@ -127,10 +127,11 @@ describe("Language Servers page settings", () => {
     expect(stagedFor("languageServers.basedpyright.enabled")).toBe(false);
     expect(stagedFor("languageServers.pyright.enabled")).toBe(true);
     expect(stagedFor("languageServers.ty.enabled")).toBe(false);
+    expect(stagedFor("languageServers.pyrefly.enabled")).toBe(false);
     expect(picker).toHaveTextContent("Pyright");
     await user.click(picker);
     await user.click(screen.getByRole("option", { name: /Automatic/ }));
-    for (const name of ["basedpyright", "pyright", "ty"]) {
+    for (const name of ["basedpyright", "pyright", "ty", "pyrefly"]) {
       expect(stagedFor(`languageServers.${name}.enabled`)).toBe(true);
     }
   });

src/features/tools/backend.ts

@@ -94,13 +94,20 @@ export function sampleTools(): ToolInfo[] {
       version: "4.3.3",
       path: "/opt/homebrew/bin/typescript-language-server",
     }),
-    ...["basedpyright", "pyright", "ty"].map((name) =>
+    ...["basedpyright", "pyright", "ty", "pyrefly"].map((name) =>
       tool({
         name,
-        displayName: name === "pyright" ? "Pyright" : name === "ty" ? "ty (Python)" : name,
+        displayName:
+          name === "pyright"
+            ? "Pyright"
+            : name === "ty"
+              ? "ty (Python)"
+              : name === "pyrefly"
+                ? "Pyrefly (Python)"
+                : name,
         languages: ["Python"],
         installMethod: "uv (virtualenv)",
-        alternatives: ["basedpyright", "pyright", "ty"],
+        alternatives: ["basedpyright", "pyright", "ty", "pyrefly"],
       }),
     ),
     tool({ name: "gopls", languages: ["Go"], installMethod: "go install" }),