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bpo-40612: Fix SyntaxError edge cases in traceback formatting (GH-20072) 

This fixes both the traceback.py module and the C code for formatting syntax errors (in Python/pythonrun.c). They now both consistently do the following:

- Suppress caret if it points left of text
- Allow caret pointing just past end of line
- If caret points past end of line, clip to *just* past end of line

The syntax error formatting code in traceback.py was mostly rewritten; small, subtle changes were applied to the C code in pythonrun.c.

There's still a difference when the text contains embedded newlines. Neither handles these very well, and I don't think the case occurs in practice.

Automerge-Triggered-By: @gvanrossum
This commit is contained in:
Guido van Rossum 2020-05-14 19:22:48 -07:00 committed by GitHub
parent 1aa8767baf
commit 15bc9ab301
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
5 changed files with 96 additions and 41 deletions
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2
Lib/test/test_cmd_line_script.py
View File

@ -633,7 +633,7 @@ class CmdLineTest(unittest.TestCase):
stderr.splitlines()[-3:],
[
b' foo"""',
b' ^',
b' ^',
b'SyntaxError: f-string: empty expression not allowed',
],
)

34
Lib/test/test_traceback.py
View File

@ -58,13 +58,13 @@ class TracebackCases(unittest.TestCase):
SyntaxError)
self.assertIn("^", err[2]) # third line has caret
self.assertEqual(err[2].count('\n'), 1) # and no additional newline
self.assertEqual(err[1].find("+"), err[2].find("^")) # in the right place
self.assertEqual(err[1].find("+") + 1, err[2].find("^")) # in the right place
err = self.get_exception_format(self.syntax_error_with_caret_non_ascii,
SyntaxError)
self.assertIn("^", err[2]) # third line has caret
self.assertEqual(err[2].count('\n'), 1) # and no additional newline
self.assertEqual(err[1].find("+"), err[2].find("^")) # in the right place
self.assertEqual(err[1].find("+") + 1, err[2].find("^")) # in the right place
def test_nocaret(self):
exc = SyntaxError("error", ("x.py", 23, None, "bad syntax"))
@ -78,14 +78,13 @@ class TracebackCases(unittest.TestCase):
self.assertEqual(len(err), 4)
self.assertEqual(err[1].strip(), "print(2)")
self.assertIn("^", err[2])
self.assertEqual(err[1].find(")"), err[2].find("^"))
self.assertEqual(err[1].find(")") + 1, err[2].find("^"))
# No caret for "unexpected indent"
err = self.get_exception_format(self.syntax_error_bad_indentation2,
IndentationError)
self.assertEqual(len(err), 4)
self.assertEqual(len(err), 3)
self.assertEqual(err[1].strip(), "print(2)")
self.assertIn("^", err[2])
self.assertEqual(err[1].find("p"), err[2].find("^"))
def test_base_exception(self):
# Test that exceptions derived from BaseException are formatted right
@ -656,7 +655,7 @@ class BaseExceptionReportingTests:
self.assertIn('inner_raise() # Marker', blocks[2])
self.check_zero_div(blocks[2])
@support.skip_if_new_parser("Pegen is arguably better here, so no need to fix this")
@unittest.skipIf(support.use_old_parser(), "Pegen is arguably better here, so no need to fix this")
def test_syntax_error_offset_at_eol(self):
# See #10186.
def e():
@ -666,7 +665,7 @@ class BaseExceptionReportingTests:
def e():
exec("x = 5 | 4 |")
msg = self.get_report(e).splitlines()
self.assertEqual(msg[-2], ' ^')
self.assertEqual(msg[-2], ' ^')
def test_message_none(self):
# A message that looks like "None" should not be treated specially
@ -679,6 +678,25 @@ class BaseExceptionReportingTests:
err = self.get_report(Exception(''))
self.assertIn('Exception\n', err)
def test_syntax_error_various_offsets(self):
for offset in range(-5, 10):
for add in [0, 2]:
text = " "*add + "text%d" % offset
expected = [' File "file.py", line 1']
if offset < 1:
expected.append(" %s" % text.lstrip())
elif offset <= 6:
expected.append(" %s" % text.lstrip())
expected.append(" %s^" % (" "*(offset-1)))
else:
expected.append(" %s" % text.lstrip())
expected.append(" %s^" % (" "*5))
expected.append("SyntaxError: msg")
expected.append("")
err = self.get_report(SyntaxError("msg", ("file.py", 1, offset+add, text)))
exp = "\n".join(expected)
self.assertEqual(exp, err)
class PyExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
#

29
Lib/traceback.py
View File

@ -569,23 +569,30 @@ class TracebackException:
if not issubclass(self.exc_type, SyntaxError):
yield _format_final_exc_line(stype, self._str)
return
else:
yield from self._format_syntax_error(stype)
# It was a syntax error; show exactly where the problem was found.
def _format_syntax_error(self, stype):
"""Format SyntaxError exceptions (internal helper)."""
# Show exactly where the problem was found.
filename = self.filename or "<string>"
lineno = str(self.lineno) or '?'
yield ' File "{}", line {}\n'.format(filename, lineno)
badline = self.text
offset = self.offset
if badline is not None:
yield ' {}\n'.format(badline.strip())
if offset is not None:
caretspace = badline.rstrip('\n')
offset = min(len(caretspace), offset) - 1
caretspace = caretspace[:offset].lstrip()
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.isspace() and c or ' ') for c in caretspace)
caretspace = ((c if c.isspace() else ' ') for c in ltext[:caret])
yield ' {}^\n'.format(''.join(caretspace))
msg = self.msg or "<no detail available>"
yield "{}: {}\n".format(stype, msg)

2
Misc/NEWS.d/next/Library/2020-05-13-10-23-29.bpo-40612.gOIreM.rst Normal file
View File

@ -0,0 +1,2 @@
Fix edge cases in SyntaxError formatting. If the offset is <= 0, no caret is printed.
If the offset is > line length, the caret is printed pointing just after the last character.

70
Python/pythonrun.c
View File

@ -554,37 +554,65 @@ finally:
static void
print_error_text(PyObject *f, int offset, PyObject *text_obj)
{
const char *text;
const char *nl;
text = PyUnicode_AsUTF8(text_obj);
/* Convert text to a char pointer; return if error */
const char *text = PyUnicode_AsUTF8(text_obj);
if (text == NULL)
return;
if (offset >= 0) {
if (offset > 0 && (size_t)offset == strlen(text) && text[offset - 1] == '\n')
offset--;
for (;;) {
nl = strchr(text, '\n');
if (nl == NULL || nl-text >= offset)
break;
offset -= (int)(nl+1-text);
text = nl+1;
}
while (*text == ' ' || *text == '\t' || *text == '\f') {
text++;
offset--;
}
/* Convert offset from 1-based to 0-based */
offset--;
/* Strip leading whitespace from text, adjusting offset as we go */
while (*text == ' ' || *text == '\t' || *text == '\f') {
text++;
offset--;
}
/* Calculate text length excluding trailing newline */
Py_ssize_t len = strlen(text);
if (len > 0 && text[len-1] == '\n') {
len--;
}
/* Clip offset to at most len */
if (offset > len) {
offset = len;
}
/* Skip past newlines embedded in text */
for (;;) {
const char *nl = strchr(text, '\n');
if (nl == NULL) {
break;
}
Py_ssize_t inl = nl - text;
if (inl >= (Py_ssize_t)offset) {
break;
}
inl += 1;
text += inl;
len -= inl;
offset -= (int)inl;
}
/* Print text */
PyFile_WriteString(" ", f);
PyFile_WriteString(text, f);
if (*text == '\0' || text[strlen(text)-1] != '\n')
/* Make sure there's a newline at the end */
if (text[len] != '\n') {
PyFile_WriteString("\n", f);
if (offset == -1)
}
/* Don't print caret if it points to the left of the text */
if (offset < 0)
return;
/* Write caret line */
PyFile_WriteString(" ", f);
while (--offset > 0)
while (--offset >= 0) {
PyFile_WriteString(" ", f);
}
PyFile_WriteString("^\n", f);
}