Backport PR #8843: don't strip encoding cookie from cell magics

closes  #8841

IPython/core/inputsplitter.py

@@ -484,8 +484,8 b' class IPythonInputSplitter(InputSplitter):'
                                              leading_indent(),
                                              classic_prompt(),
                                              ipy_prompt(),
-                                             strip_encoding_cookie(),
                                              cellmagic(end_on_blank_line=line_input_checker),
+                                             strip_encoding_cookie(),
                                             ]
         
         self.assemble_logical_lines = assemble_logical_lines()

IPython/core/tests/test_inputsplitter.py

@@ -496,7 +496,7 b' class IPythonInputTestCase(InputSplitterTestCase):'
 if __name__ == '__main__':
     # A simple demo for interactive experimentation.  This code will not get
     # picked up by any test suite.
-    from IPython.core.inputsplitter import InputSplitter, IPythonInputSplitter
+    from IPython.core.inputsplitter import IPythonInputSplitter
 
     # configure here the syntax to use, prompt and whether to autoindent
     #isp, start_prompt = InputSplitter(), '>>> '
@@ -592,6 +592,16 b' class CellModeCellMagics(CellMagicsCommon, unittest.TestCase):'
         sp.push('\n')
         # This should accept a blank line and carry on until the cell is reset
         nt.assert_true(sp.push_accepts_more()) #3
+    
+    def test_no_strip_coding(self):
+        src = '\n'.join([
+            '%%writefile foo.py',
+            '# coding: utf-8',
+            'print(u"üñîçø∂é")',
+        ])
+        out = self.sp.transform_cell(src)
+        nt.assert_in('# coding: utf-8', out)
+
 
 class LineModeCellMagics(CellMagicsCommon, unittest.TestCase):
     sp = isp.IPythonInputSplitter(line_input_checker=True)