fix: a fake stdout might not have isatty

CHANGES.rst

@@ -20,7 +20,9 @@ development at the same time, such as 4.5.x and 5.0.
 Unreleased
 ----------
 
-Nothing yet.
+- Fix: ``html_report()`` could fail with an AttributeError on ``isatty`` if run
+  in an unusual environment where sys.stdout had been replaced.  This is now
+  fixed.
 
 
 .. scriv-start-here

coverage/misc.py

@@ -394,7 +394,7 @@ def stdout_link(text: str, url: str) -> str:
     If attached to a terminal, use escape sequences. Otherwise, just return
     the text.
     """
-    if sys.stdout.isatty():
+    if hasattr(sys.stdout, "isatty") and sys.stdout.isatty():
         return f"\033]8;;{url}\a{text}\033]8;;\a"
     else:
         return text

tests/test_misc.py

@@ -6,6 +6,7 @@
 from __future__ import annotations
 
 import sys
+from typing import Any
 from unittest import mock
 
 import pytest
@@ -165,3 +166,19 @@ def test_stdout_link_tty() -> None:
 def test_stdout_link_not_tty() -> None:
     # Without mocking isatty, it reports False in a pytest suite.
     assert stdout_link("some text", "some url") == "some text"
+
+
+def test_stdout_link_with_fake_stdout() -> None:
+    # If stdout is another object, we should still be ok.
+    class FakeStdout:
+        """New stdout, has .write(), but not .isatty()."""
+        def __init__(self, f: Any) -> None:
+            self.f = f
+
+        def write(self, data: str) -> Any:
+            """Write through to the underlying file."""
+            return self.f.write(data)
+
+    with mock.patch.object(sys, "stdout", FakeStdout(sys.stdout)):
+        link = stdout_link("some text", "some url")
+    assert link == "some text"