mirror of
https://github.com/lightpanda-io/browser.git
synced 2026-06-11 01:25:53 -04:00
eval: support top-level await and return
Falls back to compiling the script inside an async IIFE if the initial block-scoped compilation fails. This enables top-level await and return statements directly in the eval tool.
This commit is contained in:
Adrià Arrufat
@@ -192,22 +192,21 @@ the end of the call. Adding a key (`lp.x = …`), updating a nested value
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update — even after a navigation, because the store lives Session-side,
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not on the page.
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**Async eval.** If your `/eval` body returns a Promise, `runEval`
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pumps the event loop until it settles, then surfaces the resolved value
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(or the rejection as an error). Combined with the bridge this lets a
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single `/eval` do an async `fetch` loop over `lp.*` data:
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**Async eval.** Top-level `await` works directly — the body runs as an
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async function, so use `return` to produce a value. `runEval` pumps the
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event loop until it settles, then surfaces the resolved value (or the
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rejection as an error). Combined with the bridge this lets a single
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`/eval` do an async `fetch` loop over `lp.*` data:
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```pandascript
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/eval '''
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(async () => {
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for (const s of lp.front.stories) {
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const html = await fetch('/item?id=' + s.id).then(r => r.text());
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const doc = new DOMParser().parseFromString(html, 'text/html');
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s.comments = [...doc.querySelectorAll('tr.athing.comtr')].slice(0, 3)
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.map(r => r.querySelector('.commtext')?.textContent.trim())
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.filter(Boolean);
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}
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})()
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for (const s of lp.front.stories) {
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const html = await fetch('/item?id=' + s.id).then(r => r.text());
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const doc = new DOMParser().parseFromString(html, 'text/html');
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s.comments = [...doc.querySelectorAll('tr.athing.comtr')].slice(0, 3)
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.map(r => r.querySelector('.commtext')?.textContent.trim())
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.filter(Boolean);
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}
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'''
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/eval '''
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@@ -215,9 +214,9 @@ JSON.stringify(lp.front.stories)
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'''
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```
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An async IIFE with no explicit `return` resolves to `undefined`, which
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the eval treats as silent — so the loop above prints nothing, and only
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the final `JSON.stringify` lands on stdout.
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A body with no explicit `return` resolves to `undefined`, which the eval
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treats as silent — so the loop above prints nothing, and only the final
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`JSON.stringify` lands on stdout.
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The store is **script-run scoped**: it's bound to the Session that runs
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the script, and goes away when that Session does. There is no
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@@ -192,7 +192,7 @@ pub const Tool = enum {
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.input_schema = url_params_schema,
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},
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.eval => .{
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.description = "Evaluate JavaScript in the current page context. If a url is provided, it navigates to that url first. The `globalThis.lp` object exposes a Session-scoped bridge store: values written via `lp.foo = ...` auto-sync at end of eval, surviving navigation; values previously set via `/extract save=` or `/eval save=` appear as `lp.<name>`.",
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.description = "Evaluate JavaScript in the current page context. A bare trailing expression yields its value; top-level `await` and `return` are supported (the body then runs as an async function, so use `return` to produce a value). If a url is provided, it navigates to that url first. The `globalThis.lp` object exposes a Session-scoped bridge store: values written via `lp.foo = ...` auto-sync at end of eval, surviving navigation; values previously set via `/extract save=` or `/eval save=` appear as `lp.<name>`.",
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.summary = "Run JavaScript in the page",
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.input_schema = minify(
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\\{
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@@ -659,7 +659,7 @@ pub fn evalScript(
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) ToolError!ToolResult {
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const z = try arena.dupeZ(u8, script);
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const page = try ensurePage(session, registry, null, null, null);
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return runEval(arena, page, z);
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return runEval(arena, page, z, null);
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}
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/// Schema-driven extraction. The schema is parsed in Zig so a syntax error
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@@ -678,7 +678,7 @@ pub fn extract(
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const script = try std.mem.concatWithSentinel(arena, u8, &.{ schema_walker_prefix, schema_json, schema_walker_suffix }, 0);
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const page = try ensurePage(session, registry, null, null, null);
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return runEval(arena, page, script);
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return runEval(arena, page, script, null);
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}
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// The schema literal is spliced between prefix and suffix verbatim — a format
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@@ -960,31 +960,27 @@ fn execEval(arena: std.mem.Allocator, session: *lp.Session, registry: *CDPNode.R
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const app_allocator = session.browser.app.allocator;
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const prelude = bridgePrelude(arena, &session.bridge_store) catch return ToolError.OutOfMemory;
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_ = try runEval(arena, page, prelude);
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_ = try runEval(arena, page, prelude, null);
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// Block-scope so top-level `let`/`const` don't leak across calls.
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// Block scope preserves a trailing expression's value and keeps top-level
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// `let`/`const` from leaking; top-level `await`/`return` need the async IIFE.
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const block_script = std.fmt.allocPrintSentinel(
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arena,
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"{{\n{s}\n}}",
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.{args.script},
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0,
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) catch return ToolError.OutOfMemory;
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var result = try runEval(arena, page, block_script);
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// Recover from top-level `return` by retrying inside an IIFE.
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if (result.is_error == true and std.mem.indexOf(u8, result.text, "Illegal return statement") != null) {
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const iife_script = std.fmt.allocPrintSentinel(
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arena,
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"(function(){{ \"use strict\"; {s} }})()",
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.{args.script},
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0,
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) catch return ToolError.OutOfMemory;
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result = try runEval(arena, page, iife_script);
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}
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if (result.is_error == true) return result;
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const iife_script = std.fmt.allocPrintSentinel(
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arena,
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"(async function(){{ \"use strict\"; {s} }})()",
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.{args.script},
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0,
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) catch return ToolError.OutOfMemory;
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var result = try runEval(arena, page, block_script, iife_script);
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if (result.is_error) return result;
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// Sync lp.* before any queued navigation tears down this JS context.
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const postlude_result: ?ToolResult = runEval(arena, page, bridge_postlude) catch |err| switch (err) {
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const postlude_result: ?ToolResult = runEval(arena, page, bridge_postlude, null) catch |err| switch (err) {
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error.OutOfMemory => return ToolError.OutOfMemory,
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else => null,
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};
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@@ -1043,7 +1039,9 @@ fn execExtract(arena: std.mem.Allocator, session: *lp.Session, registry: *CDPNod
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const eval_promise_timeout_ms: u32 = 30_000;
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fn runEval(arena: std.mem.Allocator, page: *lp.Frame, script: [:0]const u8) ToolError!ToolResult {
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/// Runs `fallback` only if `script` fails to *compile* — a compile failure ran
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/// nothing, so retrying is safe; a runtime throw keeps `script`'s error.
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fn runEval(arena: std.mem.Allocator, page: *lp.Frame, script: [:0]const u8, fallback: ?[:0]const u8) ToolError!ToolResult {
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var ls: lp.js.Local.Scope = undefined;
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page.js.localScope(&ls);
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defer ls.deinit();
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@@ -1052,8 +1050,10 @@ fn runEval(arena: std.mem.Allocator, page: *lp.Frame, script: [:0]const u8) Tool
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try_catch.init(&ls.local);
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defer try_catch.deinit();
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const js_result = ls.local.compileAndRun(script, null) catch |err|
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const js_result = ls.local.compileAndRun(script, null) catch |err| {
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if (err == error.CompilationError) if (fallback) |fb| return runEval(arena, page, fb, null);
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return .{ .text = try formatJsError(arena, &try_catch, err), .is_error = true };
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};
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if (js_result.isPromise()) {
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const promise = js_result.toPromise();
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@@ -477,7 +477,7 @@ test "MCP - eval error reporting" {
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} }, out.written());
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}
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test "MCP - eval: top-level return retried inside IIFE" {
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test "MCP - eval: top-level return runs in an async wrapper" {
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defer testing.reset();
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var out: std.io.Writer.Allocating = .init(testing.arena_allocator);
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const server = try testLoadPage("about:blank", &out.writer);
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@@ -501,6 +501,30 @@ test "MCP - eval: top-level return retried inside IIFE" {
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} }, out.written());
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}
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test "MCP - eval: top-level await runs in an async wrapper" {
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defer testing.reset();
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var out: std.io.Writer.Allocating = .init(testing.arena_allocator);
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const server = try testLoadPage("about:blank", &out.writer);
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defer server.deinit();
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const msg =
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\\{
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\\ "jsonrpc": "2.0",
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\\ "id": 1,
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\\ "method": "tools/call",
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\\ "params": {
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\\ "name": "eval",
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\\ "arguments": { "script": "const v = await Promise.resolve(41); return v + 1;" }
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\\ }
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\\}
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;
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try router.handleMessage(server, testing.arena_allocator, msg);
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try testing.expectJson(.{ .id = 1, .result = .{
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.content = &.{.{ .type = "text", .text = "42" }},
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} }, out.written());
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}
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test "MCP - eval: let declaration does not leak across calls" {
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defer testing.reset();
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var out: std.io.Writer.Allocating = .init(testing.arena_allocator);
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