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Blockers for colored tracebacks (#5699)

Original issue. Resolved in the reported scope. All four listed blockers execute successfully. Colored traceback APIs and four actual uncaught exception paths match CPython, including builtin and missing-stdlib suggestions.

Environment

  • Source and standard library: f39b054b9c8c.
  • Verified October 5, 2026 on macOS 26.5.2 ARM64.
  • RustPython: 0.6.1, Python 3.14.0.alpha; x86_64 through Rosetta.
  • Comparison: CPython 3.14.6 ARM64.

Use absolute paths for the variables below:

  • RP: the RustPython executable for this commit.
  • CP: the CPython 3.14.6 executable.
  • SRC: the source directory at this commit, including its matching Lib.
  • CASE: the directory containing the files shown below.

Shell variables replace recorded absolute paths. Export them so the Python inputs can use them:

export RP CP SRC CASE
unset PYTHONPATH PYTHONHOME PYTHONWARNINGS PYTHONSTARTUP
export PYTHONDONTWRITEBYTECODE=1
export LANG=en_US.UTF-8 LC_NUMERIC=en_US.UTF-8

LC_ALL was unset in these recorded runs.

unset LC_ALL

Reproducer

Save as probe-traceback-blockers.py.

import sys
import json
import builtins
import traceback
import ast


class Point:
    __match_args__ = ("x", "y")

    def __init__(self, x, y):
        self.x, self.y = x, y


match Point(3, 4):
    case Point(3, y=answer):
        assert answer == 4
    case _:
        raise AssertionError("class pattern did not execute")

assert sys._getframe().f_builtins["len"] is len
custom = {"__builtins__": {"custom_marker": 42}, "frame": sys._getframe}
exec("actual = frame().f_builtins", custom)
assert custom["actual"] is custom["__builtins__"]
assert isinstance(sys.stdlib_module_names, frozenset)
assert {"sys", "io", "_io", "traceback"} <= sys.stdlib_module_names

handled = []
try:
    raise ExceptionGroup("split", [ValueError("v"), TypeError("t")])
except* ValueError as exc:
    handled.append(("value", len(exc.exceptions)))
except* TypeError as exc:
    handled.append(("type", len(exc.exceptions)))
assert handled == [("value", 1), ("type", 1)]

anchors = traceback._extract_caret_anchors_from_line_segment("x + y")
assert anchors is not None, "actual traceback class-pattern branch failed"
records = {
    "class_match": answer,
    "builtins": True,
    "stdlib_module_names": True,
    "except_star": handled,
    "anchors": list(anchors),
}


def zero():
    return 1 / 0


def builtins_typo():
    return ZeroDivisionErrrrr


def stdlib_missing():
    return io.StringIO()


def group():
    raise ExceptionGroup("colored group", [ValueError("v"), TypeError("t")])


for label, function, needle in (
    ("zero", zero, "ZeroDivisionError"),
    ("builtins_typo", builtins_typo, "Did you mean: 'ZeroDivisionError'?"),
    ("stdlib_missing", stdlib_missing, "forget to import 'io'"),
    ("group", group, "ExceptionGroup"),
):
    try:
        function()
    except Exception as exc:
        plain = "".join(traceback.format_exception(exc, colorize=False))
        colored = "".join(traceback.format_exception(exc, colorize=True))
        assert needle in plain, (label, plain)
        assert "\x1b[" in colored, (label, colored)
        assert needle in colored or label == "zero", (label, colored)
        records[label] = {"plain": plain, "colored": colored}
print(json.dumps(records, ensure_ascii=True, indent=2))

Run

cd "$SRC"

RustPython:

RUSTPYTHONPATH="$SRC/Lib" "$RP" -B "$CASE/probe-traceback-blockers.py"

CPython:

"$CP" -B "$CASE/probe-traceback-blockers.py"

Results

Expected: Class-pattern code generation, frame.f_builtins, sys.stdlib_module_names and except* code generation must support traceback rendering.

RustPython and CPython 3.14.6

Exit code: 0. No timeout.

stdout:

class_match: 4
builtins: True
stdlib_module_names: True
except_star: [['value', 1], ['type', 1]]
anchors: [0, 2, 0, 3, '~', '^']
zero: ANSI color sequences present=True
builtins_typo: ANSI color sequences present=True
stdlib_missing: ANSI color sequences present=True
group: ANSI color sequences present=True

This summarizes the recorded traceback checks; the code above includes the exact assertions.

stderr:

No output.

Historical failure

Previously recorded at a7ad84827023; exit code 1. This run was not repeated alongside the current results. Historical inputs may differ from the expanded checks above.

stdout: No output.

stderr:

Traceback (most recent call last):
  File "<survey>/verification-tools/derived-main/issue-5699-case-01.py", line 6, in <module>
    case C(x):
ValueError: not enough values to unpack (expected 1, got 0)

Uncaught-exception check

Save as probe-traceback-uncaught.py:

import sys

if sys.argv[1] == "builtin":
    ZeroDivisionErrrrr
elif sys.argv[1] == "stdlib":
    io.StringIO()
elif sys.argv[1] == "zero":
    1 / 0
else:
    raise ExceptionGroup("uncaught group", [ValueError("v"), TypeError("t")])
for case in builtin stdlib zero group; do
  RUSTPYTHONPATH="$SRC/Lib" PYTHON_COLORS=1 FORCE_COLOR=1 \
    "$RP" -B "$CASE/probe-traceback-uncaught.py" "$case"
  PYTHON_COLORS=1 FORCE_COLOR=1 \
    "$CP" -B "$CASE/probe-traceback-uncaught.py" "$case"
done

Each of the eight recorded processes exited 1, as expected for uncaught exceptions. All emitted ANSI-colored tracebacks. The builtin typo suggested ZeroDivisionError, the missing module suggested importing io, division by zero reported ZeroDivisionError, and the group displayed both child exceptions.

Historical output excerpt; runner metadata and repeated shutdown warnings are omitted.

Related change and scope

PR #6110: class-pattern code generation; PR #6568: provide both frame.f_builtins and sys.stdlib_module_names; PR #6530: except* code generation and exception-group handling.

The eight uncaught-exception processes correctly exit 1. The check does not certify every traceback edge case or terminal.

First fixing commit: not established.

Evidence

Recorded executable SHA-256 values:

AI assistance: OpenAI Codex.