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bpo-34588: Fix an off-by-one error in traceback formatting. (GH-9077)

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The recursive frame pruning code always undercounted the number of elided frames
by one. That is, in the "[Previous line repeated N more times]" message, N would
always be one too few. Near the recursive pruning cutoff, one frame could be
silently dropped. That situation is demonstrated in the OP of the bug report.

The fix is to start the identical frame counter at 1.
This commit is contained in:
Benjamin Peterson 2018-09-10 08:43:10 -07:00 • committed by GitHub
parent 54752533b2
commit d545869d08
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GPG key ID: 4AEE18F83AFDEB23
4 changed files with 96 additions and 26 deletions
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30
Python/traceback.c
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@ -511,16 +511,21 @@ tb_displayline(PyObject *f, PyObject *filename, int lineno, PyObject *name)
return err;
}
static const int TB_RECURSIVE_CUTOFF = 3; // Also hardcoded in traceback.py.
static int
tb_print_line_repeated(PyObject *f, long cnt)
{
int err;
cnt -= TB_RECURSIVE_CUTOFF;
PyObject *line = PyUnicode_FromFormat(
" [Previous line repeated %ld more times]\n", cnt-3);
(cnt > 1)
? " [Previous line repeated %ld more times]\n"
: " [Previous line repeated %ld more time]\n",
cnt);
if (line == NULL) {
return -1;
}
err = PyFile_WriteObject(line, f, Py_PRINT_RAW);
int err = PyFile_WriteObject(line, f, Py_PRINT_RAW);
Py_DECREF(line);
return err;
}
@ -544,15 +549,11 @@ tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
tb = tb->tb_next;
}
while (tb != NULL && err == 0) {
if (last_file != NULL &&
tb->tb_frame->f_code->co_filename == last_file &&
last_line != -1 && tb->tb_lineno == last_line &&
last_name != NULL && tb->tb_frame->f_code->co_name == last_name)
{
cnt++;
}
else {
if (cnt > 3) {
if (last_file == NULL ||
tb->tb_frame->f_code->co_filename != last_file ||
last_line == -1 || tb->tb_lineno != last_line ||
last_name == NULL || tb->tb_frame->f_code->co_name != last_name) {
if (cnt > TB_RECURSIVE_CUTOFF) {
err = tb_print_line_repeated(f, cnt);
}
last_file = tb->tb_frame->f_code->co_filename;
@ -560,7 +561,8 @@ tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
last_name = tb->tb_frame->f_code->co_name;
cnt = 0;
}
if (err == 0 && cnt < 3) {
cnt++;
if (err == 0 && cnt <= TB_RECURSIVE_CUTOFF) {
err = tb_displayline(f,
tb->tb_frame->f_code->co_filename,
tb->tb_lineno,
@ -571,7 +573,7 @@ tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
}
tb = tb->tb_next;
}
if (err == 0 && cnt > 3) {
if (err == 0 && cnt > TB_RECURSIVE_CUTOFF) {
err = tb_print_line_repeated(f, cnt);
}
return err;