Allow InputTransformers to raise SyntaxErrors

This is a relatively trivial modification of the IPython main loop to
catch a possible SyntaxError and print it instead of
quitting. Doctesting this change is somewhat tricky since we actually
need to run the main TerminalInteractiveShell.interact() loop, and is
done through a subprocess and piping in a testcase.

IPython/core/tests/test_application.py

@@ -3,9 +3,13 b''
 
 import os
 import tempfile
+import shutil
+
+import nose.tools as nt
 
 from IPython.core.application import BaseIPythonApplication
 from IPython.testing import decorators as dec
+from IPython.testing.tools import make_tempfile, ipexec
 from IPython.utils import py3compat
 
 @dec.onlyif_unicode_paths
@@ -48,3 +52,46 b' def test_unicode_ipdir():'
             os.environ["IPYTHONDIR"] = old_ipdir1
         if old_ipdir2:
             os.environ["IPYTHONDIR"] = old_ipdir2
+
+
+
+TEST_SYNTAX_ERROR_CMDS = """
+from IPython.core.inputtransformer import InputTransformer
+
+%cpaste
+class SyntaxErrorTransformer(InputTransformer):
+
+    def push(self, line):
+        if 'syntaxerror' in line:
+            raise SyntaxError('in input '+line)
+        return line
+
+    def reset(self):
+        pass
+--
+
+ip = get_ipython()
+transformer = SyntaxErrorTransformer()
+ip.input_splitter.python_line_transforms.append(transformer)
+ip.input_transformer_manager.python_line_transforms.append(transformer)
+
+# now the actual commands
+1234
+2345  # syntaxerror <- triggered here
+3456
+"""
+
+def test_syntax_error():
+    """Check that IPython does not abort if a SyntaxError is raised in an InputTransformer"""
+    try:
+        tmp = tempfile.mkdtemp()
+        filename = os.path.join(tmp, 'test_syntax_error.py')
+        with open(filename, 'w') as f:
+            f.write(TEST_SYNTAX_ERROR_CMDS)
+        out, err = ipexec(filename, pipe=True)
+        nt.assert_equal(err, '')
+        nt.assert_in('1234', out)
+        nt.assert_in('SyntaxError: in input 2345  # syntaxerror <- triggered here', out)
+        nt.assert_in('3456', out)
+    finally:
+        shutil.rmtree(tmp)

IPython/terminal/interactiveshell.py

@@ -541,8 +541,13 b' class TerminalInteractiveShell(InteractiveShell):'
                 # asynchronously by signal handlers, for example.
                 self.showtraceback()
             else:
-                self.input_splitter.push(line)
-                more = self.input_splitter.push_accepts_more()
+                try:
+                    self.input_splitter.push(line)
+                    more = self.input_splitter.push_accepts_more()
+                except SyntaxError:
+                    self.showsyntaxerror()
+                    self.input_splitter.reset()
+                    more = False
                 if (self.SyntaxTB.last_syntax_error and
                     self.autoedit_syntax):
                     self.edit_syntax_error()

IPython/testing/tools.py

@@ -173,7 +173,7 b' def get_ipython_cmd(as_string=False):'
 
     return ipython_cmd
 
-def ipexec(fname, options=None):
+def ipexec(fname, options=None, pipe=False):
     """Utility to call 'ipython filename'.
 
     Starts IPython with a minimal and safe configuration to make startup as fast
@@ -189,6 +189,9 b' def ipexec(fname, options=None):'
     options : optional, list
       Extra command-line flags to be passed to IPython.
 
+    pipe : optional, boolean
+      Pipe fname into IPython as stdin instead of calling it as external file
+
     Returns
     -------
     (stdout, stderr) of ipython subprocess.
@@ -208,8 +211,12 b' def ipexec(fname, options=None):'
     ipython_cmd = get_ipython_cmd()
     # Absolute path for filename
     full_fname = os.path.join(test_dir, fname)
-    full_cmd = ipython_cmd + cmdargs + [full_fname]
-    p = Popen(full_cmd, stdout=PIPE, stderr=PIPE)
+    if pipe:
+        full_cmd = ipython_cmd + cmdargs
+        p = Popen(full_cmd, stdin=open(full_fname), stdout=PIPE, stderr=PIPE)
+    else:
+        full_cmd = ipython_cmd + cmdargs + [full_fname]
+        p = Popen(full_cmd, stdout=PIPE, stderr=PIPE)
     out, err = p.communicate()
     out, err = py3compat.bytes_to_str(out), py3compat.bytes_to_str(err)
     # `import readline` causes 'ESC[?1034h' to be output sometimes,