gh-92336: linecache.getline should not raise exceptions on decoding errors (GH-94410)

(cherry picked from commit 21cbdae)

Co-authored-by: Irit Katriel <[email protected]>

Author: miss-islington

Lib/linecache.py

@@ -135,7 +135,7 @@ def updatecache(filename, module_globals=None):
     try:
         with tokenize.open(fullname) as fp:
             lines = fp.readlines()
-    except OSError:
+    except (OSError, UnicodeDecodeError, SyntaxError):
         return []
     if lines and not lines[-1].endswith('\n'):
         lines[-1] += '\n'

Lib/test/test_linecache.py

@@ -73,12 +73,10 @@ class GetLineTestsBadData(TempFile):
     # file_byte_string = b'Bad data goes here'
 
     def test_getline(self):
-        self.assertRaises((SyntaxError, UnicodeDecodeError),
-                          linecache.getline, self.file_name, 1)
+        self.assertEqual(linecache.getline(self.file_name, 1), '')
 
     def test_getlines(self):
-        self.assertRaises((SyntaxError, UnicodeDecodeError),
-                          linecache.getlines, self.file_name)
+        self.assertEqual(linecache.getlines(self.file_name), [])
 
 
 class EmptyFile(GetLineTestsGoodData, unittest.TestCase):
@@ -92,9 +90,11 @@ class SingleEmptyLine(GetLineTestsGoodData, unittest.TestCase):
 class GoodUnicode(GetLineTestsGoodData, unittest.TestCase):
     file_list = ['á\n', 'b\n', 'abcdef\n', 'ááááá\n']
 
+class BadUnicode_NoDeclaration(GetLineTestsBadData, unittest.TestCase):
+    file_byte_string = b'\n\x80abc'
 
-class BadUnicode(GetLineTestsBadData, unittest.TestCase):
-    file_byte_string = b'\x80abc'
+class BadUnicode_WithDeclaration(GetLineTestsBadData, unittest.TestCase):
+    file_byte_string = b'# coding=utf-8\n\x80abc'
 
 
 class LineCacheTests(unittest.TestCase):

Misc/NEWS.d/next/Library/2022-06-29-09-48-37.gh-issue-92336.otA6c6.rst

@@ -0,0 +1 @@
+Fix bug where :meth:`linecache.getline` fails on bad files with :exc:`UnicodeDecodeError` or :exc:`SyntaxError`. It now returns an empty string as per the documentation.