add _format_syntax_error() to doctest, add unit test for it

akulakov · Sep 26, 2021 · Sep 26, 2021 · Sep 28, 2021 · Sep 28, 2021 · Sep 28, 2021
commit a5271379a0ef16a3d0432407566fce628369ec63
diff --git a/Lib/doctest.py b/Lib/doctest.py
@@ -101,6 +101,7 @@ def _test():
 import re
 import sys
 import traceback
+import types
 import unittest
 from io import StringIO, IncrementalNewlineDecoder
 from collections import namedtuple
@@ -241,6 +242,44 @@ def _indent(s, indent=4):
     # This regexp matches the start of non-blank lines:
     return re.sub('(?m)^(?!$)', indent*' ', s)
 
+def _traceback_format_syntax_error(self, stype):
+    """Format SyntaxError exceptions (internal helper). Copied from
+    traceback.py
+    """
+    # Show exactly where the problem was found.
+    filename_suffix = ''
+    if self.lineno is not None:
+        yield '  File "{}", line {}\n'.format(
+            self.filename or "<string>", self.lineno)
+    elif self.filename is not None:
+        filename_suffix = ' ({})'.format(self.filename)
+
+    text = self.text
+    if text is not None:
+        # text  = "   foo\n"
+        # rtext = "   foo"
+        # ltext =    "foo"
+        rtext = text.rstrip('\n')
+        ltext = rtext.lstrip(' \n\f')
+        spaces = len(rtext) - len(ltext)
+        yield '    {}\n'.format(ltext)
+        # Convert 1-based column offset to 0-based index into stripped text
+        caret = (self.offset or 0) - 1 - spaces
+        if caret >= 0:
+            # non-space whitespace (likes tabs) must be kept for alignment
+            caretspace = ((c if c.isspace() else ' ') for c in ltext[:caret])
+            yield '    {}{}\n'.format(''.join(caretspace), '^'*(self.exc_value.end_offset-self.offset))
+    msg = self.msg or "<no detail available>"
+    yield "{}: {}{}\n".format(stype, msg, filename_suffix)
+
+def _print_exception(exc, /, value, tb, limit=None, file=None, chain=True):
+    """Copied from traceback.py"""
+    value, tb = traceback._parse_value_tb(exc, value, tb)
+    te = traceback.TracebackException(type(value), value, tb, limit=limit, compact=True)
+    te._format_syntax_error = types.MethodType(_traceback_format_syntax_error, te)
+    te.exc_value = value
+    te.print(file=file, chain=chain)
+
 def _exception_traceback(exc_info):
     """
     Return a string containing a traceback message for the given
@@ -249,7 +288,7 @@ def _exception_traceback(exc_info):
     # Get a traceback message.
     excout = StringIO()
     exc_type, exc_val, exc_tb = exc_info
-    traceback.print_exception(exc_type, exc_val, exc_tb, file=excout)
+    _print_exception(exc_type, exc_val, exc_tb, file=excout)
     return excout.getvalue()
 
 # Override some StringIO methods.

diff --git a/Lib/test/test_doctest3.py b/Lib/test/test_doctest3.py
@@ -0,0 +1,21 @@
+import unittest
+import io
+import contextlib
+import doctest
+
+class Test(unittest.TestCase):
+    def test_syntax_error(self):
+        f = io.StringIO()
+        with contextlib.redirect_stdout(f):
+            try:
+                doctest.run_docstring_examples("""
+                                             >>> 1 1
+                                             """, globals())
+            except Exception as e:
+                print('!!!!!', str(e))
+        self.assertIn('''
+        1 1
+        ^^^
+    SyntaxError: invalid syntax. Perhaps you forgot a comma?''',
+        f.getvalue())
+
diff --git a/Misc/NEWS.d/next/Library/2021-09-26-09-56-46.bpo-45249.RG5p25.rst b/Misc/NEWS.d/next/Library/2021-09-26-09-56-46.bpo-45249.RG5p25.rst
@@ -0,0 +1,2 @@
+Fixed display of :exc:`SyntaxError` errors in :mod:`doctest` to show full
+error range indicator rather than a single caret (``^``).
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fixed display of :exc:`SyntaxError` errors in :mod:`doctest` to show full
		error range indicator rather than a single caret (``^``).