call close on the underlying stream even if flush raises (closes #16597)

Patch by Serhiy Storchaka.

Lib/_pyio.py

@@ -346,8 +346,10 @@ class IOBase(metaclass=abc.ABCMeta):
         This method has no effect if the file is already closed.
         """
         if not self.__closed:
-            self.flush()
-            self.__closed = True
+            try:
+                self.flush()
+            finally:
+                self.__closed = True
 
     def __del__(self):
         """Destructor.  Calls close()."""
@@ -1584,8 +1586,10 @@ class TextIOWrapper(TextIOBase):
 
     def close(self):
         if self.buffer is not None and not self.closed:
-            self.flush()
-            self.buffer.close()
+            try:
+                self.flush()
+            finally:
+                self.buffer.close()
 
     @property
     def closed(self):

Lib/test/test_io.py

@@ -603,6 +603,7 @@ class IOTest(unittest.TestCase):
             raise IOError()
         f.flush = bad_flush
         self.assertRaises(IOError, f.close) # exception not swallowed
+        self.assertTrue(f.closed)
 
     def test_multi_close(self):
         f = self.open(support.TESTFN, "wb", buffering=0)
@@ -780,6 +781,22 @@ class CommonBufferedTests:
         raw.flush = bad_flush
         b = self.tp(raw)
         self.assertRaises(IOError, b.close) # exception not swallowed
+        self.assertTrue(b.closed)
+
+    def test_close_error_on_close(self):
+        raw = self.MockRawIO()
+        def bad_flush():
+            raise IOError('flush')
+        def bad_close():
+            raise IOError('close')
+        raw.close = bad_close
+        b = self.tp(raw)
+        b.flush = bad_flush
+        with self.assertRaises(IOError) as err: # exception not swallowed
+            b.close()
+        self.assertEqual(err.exception.args, ('close',))
+        self.assertEqual(err.exception.__context__.args, ('flush',))
+        self.assertFalse(b.closed)
 
     def test_multi_close(self):
         raw = self.MockRawIO()
@@ -1296,6 +1313,16 @@ class BufferedWriterTest(unittest.TestCase, CommonBufferedTests):
         with self.assertRaises(TypeError):
             self.tp(self.MockRawIO(), 8, 12)
 
+    def test_write_error_on_close(self):
+        raw = self.MockRawIO()
+        def bad_write(b):
+            raise IOError()
+        raw.write = bad_write
+        b = self.tp(raw)
+        b.write(b'spam')
+        self.assertRaises(IOError, b.close) # exception not swallowed
+        self.assertTrue(b.closed)
+
 
 class CBufferedWriterTest(BufferedWriterTest, SizeofTest):
     tp = io.BufferedWriter
@@ -2465,6 +2492,7 @@ class TextIOWrapperTest(unittest.TestCase):
             raise IOError()
         txt.flush = bad_flush
         self.assertRaises(IOError, txt.close) # exception not swallowed
+        self.assertTrue(txt.closed)
 
     def test_multi_close(self):
         txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")