Fix SyntaxError crash line to show file, line, and column

[SemTiOne]

SyntaxError crash lines now use the error's own file, line, and column instead of the location of the traceback entry where it was raised.

Before:

    E     File "package/lib.py", line 1
    E       def broken(:
    E                  ^
    E   SyntaxError: invalid syntax
    package/lib.py:1: SyntaxError

After:

    E     File "package/lib.py", line 1
    E       def broken(:
    E                  ^
    E   SyntaxError: invalid syntax
    package/lib.py:1:12: SyntaxError: invalid syntax

The traceback entry location and collection errors use the same file:line:col format. The ReprFileLocation dataclass gains an optional column field (column: int | None = None); existing output is unchanged when the field is absent.

Note: This PR doesn't solve the removal of the now-redundant File..., line N block. This is a deliberate design decision; it comes from stdlib format_exception_only(); deferred to a follow-up issue.

• Include documentation when adding new features.
• Include new tests or update existing tests when applicable.
• Allow maintainers to push and squash when merging my commits. Please uncheck this if you prefer to squash the commits yourself.
• Closes Format SyntaxErrors like Tracebacklines #2388
• If AI agents were used, they are credited in Co-authored-by commit trailers.
• Create a new changelog file in the changelog directory, with a name like <ISSUE NUMBER>.<TYPE>.rst. See changelog/README.rst for details.
• Add yourself to AUTHORS in alphabetical order.

[SemTiOne]

Hello @RonnyPfannschmidt, could you please review this PR when you have a moment? Thank you for your time.

[nicoddemus]

Move path = self._makepath(entry_path) from above to here:

Suggested change

	else:
	column = None
	else:
	path = self._makepath(entry_path)
	column = None

[SemTiOne]

Hmmm this is good. But when I think about it, is this a bandaid? Because if _syntax_error_location is ever relaxed to return loc even when exc.filename is falsy, then filename or path would evaluate the undefined path, and immediately raise a NameError? Yes mine is also a bandaid I believe, the or path is a dead code, should be deleted and be like this: self._makepath(filename)

[nicoddemus]

then filename or path would evaluate the undefined path, and immediately raise a NameError?

Not sure I follow... if _syntax_error_location changes, mypy should catch any discrepancies.

[SemTiOne]

Not sure I follow... if _syntax_error_location changes, mypy should catch any discrepancies.

Ok fair enough.

the or path is a dead code, should be deleted and be like this: self._makepath(filename)

What do you think about this?

[nicoddemus]

What do you think about this?

Let's leave it for now.

[nicoddemus]

Why the reprcrash.column guard? If not None, we call str(reprcrash) anyway.

[SemTiOne]

You are right. str(reprcrash) is safe with column=None, but the guard isn't about safety. Dropping the guard here would append a near-duplicate location line in the no-column case. The column is the signal that we have the SyntaxError's own precise location worth appending, without it we keep the existing traceback line. What do you think?

[nicoddemus]

We should make the intent more explicit then, preferably without just slapping a comment there... 🤔

[SemTiOne]

Of course, here's my code proposal, wdyt?

msg = str(repr_)
syntax_error_has_precise_location = reprcrash is not None and reprcrash.column is not None
if syntax_error_has_precise_location:
    msg += "\n" + str(reprcrash) 

[nicoddemus]

Most of the tests are constructing a SyntexError manually... can we construct them instead via actual code and exec()? Seems more resilient/reliable that way.

[nicoddemus]

Why are we raising manual SyntaxErrors here, instead of just writing code with syntax errors?

[RonnyPfannschmidt]

Thanks for picking this up — the _getreprcrash() half of this PR is exactly the right fix for #2388, and it verifies nicely: --tb=line now gives gen.py:1:12: SyntaxError: invalid syntax where main gives the useless test_raise.py:2: File "gen.py", line 1, and the short summary improves the same way. --tb=native is correctly untouched, and report serialization round-trips the new column field.

The repr_traceback_entry change, however, needs another look: it overwrites the last traceback entry's file:line with the SyntaxError's own location while the source snippet and in <funcname> still describe the real frame — so the one line editors parse for jump-to-location now points somewhere that doesn't contain the displayed code.

Reproducer (validated against the current head, 4d8030b, and against main):

# test_pr14899_repro.py
def helper():
    compile("def broken(:", "gen.py", "exec")

def test_issue1_wrong_frame_attribution():
    helper()

def test_issue3_chained_cause_link():
    try:
        compile("def broken(:", "gen.py", "exec")
    except SyntaxError as e:
        raise RuntimeError("wrapper") from e

# test_issue2_broken_syntax.py  (a real collection-time SyntaxError)
def broken(:
    pass

# test_issue7_import_no_offset.py  (import-time SyntaxError without offset)
raise SyntaxError("custom import error", ("weird.py", 3, None, "src", 3, None))

Issue 1 — frame attribution (--tb=short)

Actual (this PR):

gen.py:1:12: in helper
    compile("def broken(:", "gen.py", "exec")
E     File "gen.py", line 1
...

helper is not in gen.py, and gen.py:1 does not contain that source line. Expected — the frame keeps its real location (as on main), since the E-block and the crash line already carry the syntax-error location:

test_pr14899_repro.py:2: in helper
    compile("def broken(:", "gen.py", "exec")
E     File "gen.py", line 1
...

The same mislabelled line appears as the trailing gen.py:1:12: SyntaxError under the last frame in --tb=long and --fulltrace, and inside the "direct cause" section for the chained case (gen.py:1:12: in test_issue3_chained_cause_link).

Issue 2 — collection error mixes three files into one entry

Actual (this PR, pytest test_issue2_broken_syntax.py):

test_issue2_broken_syntax.py:1:12: in parse
    return compile(source, filename, mode, flags,
E     File ".../test_issue2_broken_syntax.py", line 1
E       def broken(:
E                  ^
E   SyntaxError: invalid syntax
test_issue2_broken_syntax.py:1:12: SyntaxError: invalid syntax

The entry line fuses the user file's location, stdlib ast.parse's function name, and stdlib source — and the location then appears three times. Expected: entry lines keep their real frames; the new file:line:col crash line appended once at the end is the actual improvement:

.../ast.py:54: in parse
    return compile(source, filename, mode, flags,
E     File ".../test_issue2_broken_syntax.py", line 1
E       def broken(:
E                  ^
E   SyntaxError: invalid syntax
test_issue2_broken_syntax.py:1:12: SyntaxError: invalid syntax

Issue 3 — the crash-line append in python.py is gated on column

test_issue7_import_no_offset.py (filename and lineno present, offset absent) gets no appended crash line at all, while issue 2's case gets one — the if reprcrash.column is not None gate should be if reprcrash is not None, and arguably the append belongs in the repr machinery rather than in importtestmodule. Expected final line:

weird.py:3: SyntaxError: custom import error

Smaller points

• raise SyntaxError(None, ("file.py", 1, 5, ...)) renders the crash line as SyntaxError: None (the E-block correctly says <no detail available>).
• offset=0 passes the is not None guard and prints a zero column (file.py:1:0: ...); 0 should probably be treated like None.
• filename or path in repr_traceback_entry is dead code — _syntax_error_location already guarantees a truthy filename.

My suggestion: drop (or narrow to the bare-typename long-style case) the repr_traceback_entry rewrite, keep _getreprcrash(), and make the collection append unconditional. That keeps every win shown in the PR description's after-example except the rewritten per-frame line, without the misattribution.

---

This analysis and comment were produced by an AI (Claude, via Claude Code) at my request; I have reviewed the findings. — Ronny