From a52506d62ff732d6c7000496757f63a309a9a6ee Mon Sep 17 00:00:00 2001
From: Pavel Feldman <pavel.feldman@gmail.com>
Date: Tue, 6 Oct 2026 15:26:08 -0700
Subject: [PATCH] fix(evaluate): serialize and parse RegExp values

Based on https://github.com/microsoft/playwright-python/pull/3189 by @FadeHack.

Fixes: https://github.com/microsoft/playwright-python/issues/3188
---
 playwright/_impl/_js_handle.py    | 14 +++++++++-
 playwright/_impl/_str_utils.py    | 12 +++++++++
 tests/async/test_page_evaluate.py | 43 +++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/playwright/_impl/_js_handle.py b/playwright/_impl/_js_handle.py
index d1e8d4fd9..db617303a 100644
--- a/playwright/_impl/_js_handle.py
+++ b/playwright/_impl/_js_handle.py
@@ -16,15 +16,17 @@
 import collections.abc
 import datetime
 import math
+import re
 import struct
 import traceback
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Union
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Pattern, Union
 from urllib.parse import ParseResult, urlparse, urlunparse
 
 from playwright._impl._connection import Channel, ChannelOwner, from_channel
 from playwright._impl._errors import Error, is_target_closed_error
 from playwright._impl._map import Map
+from playwright._impl._str_utils import escape_regex_flags, parse_regex_flags
 
 if TYPE_CHECKING:  # pragma: no cover
     from playwright._impl._element_handle import ElementHandle
@@ -182,6 +184,9 @@ def serialize_value(
         return {"s": value}
     if isinstance(value, ParseResult):
         return {"u": urlunparse(value)}
+    if isinstance(value, Pattern):
+        assert isinstance(value.pattern, str), "Only str patterns are supported."
+        return {"r": {"p": value.pattern, "f": escape_regex_flags(value)}}
 
     if value in visitor_info.visited:
         return dict(ref=visitor_info.visited[value])
@@ -247,6 +252,13 @@ def parse_value(value: Any, refs: Optional[Dict[int, Any]] = None) -> Any:
             error._stack = value["e"]["s"]
             return error
 
+        if "r" in value:
+            try:
+                return re.compile(value["r"]["p"], parse_regex_flags(value["r"]["f"]))
+            except re.error:
+                # JavaScript-only syntax, e.g. /(?<name>x)/, has no re equivalent.
+                return value
+
         if "a" in value:
             a: List = []
             refs[value["id"]] = a
diff --git a/playwright/_impl/_str_utils.py b/playwright/_impl/_str_utils.py
index 8b3e65a39..5f967b1f6 100644
--- a/playwright/_impl/_str_utils.py
+++ b/playwright/_impl/_str_utils.py
@@ -35,6 +35,18 @@ def escape_regex_flags(pattern: Pattern) -> str:
     return flags
 
 
+def parse_regex_flags(flags: str) -> int:
+    result = 0
+    if "i" in flags:
+        result |= re.IGNORECASE
+    if "s" in flags:
+        result |= re.DOTALL
+    if "m" in flags:
+        result |= re.MULTILINE
+    # The remaining JavaScript flags (d, g, u, v, y) have no re equivalent.
+    return result
+
+
 def escape_for_regex(text: str) -> str:
     return re.sub(r"[.*+?^>${}()|[\]\\]", "\\$&", text)
 
diff --git a/tests/async/test_page_evaluate.py b/tests/async/test_page_evaluate.py
index 146be6ff7..320ea0347 100644
--- a/tests/async/test_page_evaluate.py
+++ b/tests/async/test_page_evaluate.py
@@ -13,10 +13,13 @@
 # limitations under the License.
 
 import math
+import re
 from datetime import datetime, timedelta, timezone
 from typing import Optional
 from urllib.parse import ParseResult, urlparse
 
+import pytest
+
 from playwright.async_api import Error, Page
 
 
@@ -358,3 +361,43 @@ async def test_evaluate_jsonvalue_url(page: Page) -> None:
     url = urlparse("https://example.com/")
     result = await page.evaluate('() => ({ someKey: new URL("https://example.com/") })')
     assert result == {"someKey": url}
+
+
+async def test_evaluate_transfer_regex(page: Page) -> None:
+    regex = re.compile("foo.bar", re.IGNORECASE | re.MULTILINE)
+    assert await page.evaluate("a => a", regex) == regex
+
+
+async def test_evaluate_pass_regex_as_regexp(page: Page) -> None:
+    result = await page.evaluate(
+        "r => [r instanceof RegExp, r.source, r.flags, r.test('A12')]",
+        re.compile(r"a\d+", re.IGNORECASE | re.DOTALL | re.MULTILINE),
+    )
+    assert result == [True, "a\\d+", "ims", True]
+
+
+async def test_evaluate_return_regex(page: Page) -> None:
+    result = await page.evaluate(
+        "() => ({ list: [/foo/s], nested: { re: /a\\d+/gi } })"
+    )
+    assert result == {
+        "list": [re.compile("foo", re.DOTALL)],
+        "nested": {"re": re.compile(r"a\d+", re.IGNORECASE)},
+    }
+
+
+async def test_evaluate_jsonvalue_regex(page: Page) -> None:
+    handle = await page.evaluate_handle("() => ({ someKey: /foo/i })")
+    assert await handle.json_value() == {"someKey": re.compile("foo", re.IGNORECASE)}
+
+
+async def test_evaluate_return_regex_unsupported_by_python(page: Page) -> None:
+    result = await page.evaluate("() => ({ a: 1, re: /(?<year>\\d{4})/ })")
+    assert result == {"a": 1, "re": {"r": {"p": "(?<year>\\d{4})", "f": ""}}}
+
+
+async def test_evaluate_throw_for_unsupported_regex(page: Page) -> None:
+    with pytest.raises(AssertionError, match="Unexpected re.Pattern flag"):
+        await page.evaluate("a => a", re.compile("foo", re.VERBOSE))
+    with pytest.raises(AssertionError, match="Only str patterns are supported"):
+        await page.evaluate("a => a", re.compile(b"foo"))