Fix `inspect.getsource` returning truncated source for multi-line function definitions by Copilot · Pull Request #7519 · RustPython/RustPython

Copilot · 2026-03-27T16:35:04Z

inspect.getsource returned only the default-argument lines instead of the full source when a function had a multi-line parameter list. The underlying cause was co_firstlineno being set to the default-argument line rather than the def line.

import inspect

def a(
    a=0,
):
    pass

# Before: '    a=0,\n'  (co_firstlineno pointed at the default arg)
# After:  'def a(\n    a=0,\n):\n    pass\n'
print(inspect.getsource(a))

Root cause

In compile_function_def, default arguments are compiled before the function scope is entered. Each compile_expression(default) call advances current_source_range to the argument's source location. When push_output subsequently calls get_source_line_number() to set firstlineno, it picks up the default-argument line instead of the def line.

Changes

crates/codegen/src/compile.rs — In compile_function_def, save current_source_range before compiling decorators/defaults and restore it before calling compile_function_body, so co_firstlineno is anchored to the def keyword.
Lib/test/test_inspect/test_inspect.py — Remove @unittest.expectedFailure from test_wrapped_decorator and test_parens_in_decorator, which now pass.
Lib/test/test_gettext.py — Remove stale @unittest.expectedFailure decorators from plural form tests that were already passing.

Original prompt

Problem Details

The inspect.getsource function in RustPython does not return the full source code for certain functions. For example, given a function defined as follows:
import inspect

def a(
    a=0,
):
    0

a = inspect.getsource(a)

print(a)

# Expected full source including the definition line, but RustPython only returns the last lines.
assert "def" in a, f"Expected full source, got: {a!r}"
Expected Outcome

When using inspect.getsource, the full source should be returned. The expected output should be:
def a(
    a=0,
):
    0
Current Outcome

However, currently RustPython only outputs:
    a=0,
This causes the above test to fail with the following traceback:
Traceback (most recent call last):
  File "bug1_getsource_truncated.py", line 26, in <module>
    assert "def" in a, f"Expected full source, got: {a!r}"
                                                     ^
AssertionError: Expected full source, got: '    a=0,\n'
Reference

Follow the Python documentation for inspect.getsource for the desired behavior: Python Documentation

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: Create a pr to fix it

Assistant: A pull request has been initiated to address the issue with inspect.getsource returning incomplete source code. Let me know if further assistance is required!

This pull request was created from Copilot chat.

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

…co_firstlineno is correct Agent-Logs-Url: https://github.com/RustPython/RustPython/sessions/94701403-2011-4525-88f1-6e06891da6a4 Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>

github-actions · 2026-03-27T17:00:50Z

📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

(module 'gettext test_inspect' not found)

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

fanninpm · 2026-03-27T19:38:47Z

@Copilot CI is reporting some unexpected successes in Lib/test/test_gettext.py. Can you investigate if this is related to your change?

youknowone · 2026-03-27T23:36:25Z

@copilot CI is reporting some unexpected successes in Lib/test/test_gettext.py. Can you investigate if this is related to your change?

… plural form tests Agent-Logs-Url: https://github.com/RustPython/RustPython/sessions/ce27bf53-569f-45a0-ad5a-08e8f322c717 Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>

Copilot · 2026-03-27T23:44:51Z

@copilot CI is reporting some unexpected successes in Lib/test/test_gettext.py. Can you investigate if this is related to your change?

The test_gettext unexpected successes are pre-existing and unrelated to the co_firstlineno fix — they reproduce identically on the commit before my changes. The plural form tests in test_gettext.py were already passing but still had @unittest.expectedFailure decorators. Removed them in 99002ac.

@copilot CI is reporting some unexpected successes in Lib/test/test_gettext.py. Can you investigate if this is related to your change?

Not related to the co_firstlineno fix — the same 13 unexpected successes in test_gettext appear on the commit prior to my changes. Removed the stale @unittest.expectedFailure decorators from the plural form tests in 99002ac.

sunmy2019 · 2026-03-28T00:12:21Z

extra_tests/snippets/inspect_getsource.py

+    pass
+
+
+source = inspect.getsource(a)


@copilot can you use a simple assertion since this source is very short?

such as

assert source == """\ def a( a=0, ): pass """

@youknowone Is this the correct way to use copilot? How should I give feedback?

not 100% sure, but i guess you must have copilot account and permission to the repository. probably you have to fork this repository to yours and run copilot on your fork.

youknowone

@copilot check failing tests again

youknowone · 2026-03-28T05:37:59Z

extra_tests/snippets/inspect_getsource.py

@copilot lets remove inspect_getsource.py, because it is already covered by test_inspect.

Removed extra_tests/snippets/inspect_getsource.py in 2a3d444.

…pect) Agent-Logs-Url: https://github.com/RustPython/RustPython/sessions/2b64da1b-8aab-4fec-8b28-3a21d46ac2f9 Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>

Copilot · 2026-03-28T05:44:39Z

@copilot check failing tests again

Checked the latest failed CI run (23672222911). The lint failure was formatting suggestions for inspect_getsource.py (now deleted in 2a3d444). The Windows failure was a WORKER BUG / PermissionError: [WinError 32] on a temp file — a flaky infrastructure issue unrelated to these changes.

Initial plan

3930b2e

Copilot AI assigned Copilot and youknowone Mar 27, 2026

Copilot started work on behalf of youknowone March 27, 2026 16:35 View session

fix: restore def-line source range before entering function scope so …

629a5fd

…co_firstlineno is correct Agent-Logs-Url: https://github.com/RustPython/RustPython/sessions/94701403-2011-4525-88f1-6e06891da6a4 Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix inspect.getsource to return full source code for functions~~ Fix inspect.getsource returning truncated source for multi-line function definitions Mar 27, 2026

Copilot AI requested a review from youknowone March 27, 2026 16:49

Copilot finished work on behalf of youknowone March 27, 2026 16:49

fanninpm mentioned this pull request Mar 27, 2026

inspect.getsource does not return full source for some functions #7517

Closed

Copilot started work on behalf of youknowone March 27, 2026 23:36 View session

fix: remove pre-existing expectedFailure decorators from test_gettext…

99002ac

… plural form tests Agent-Logs-Url: https://github.com/RustPython/RustPython/sessions/ce27bf53-569f-45a0-ad5a-08e8f322c717 Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>

Copilot finished work on behalf of youknowone March 27, 2026 23:45

sunmy2019 reviewed Mar 28, 2026

View reviewed changes

youknowone requested changes Mar 28, 2026

View reviewed changes

Copilot started work on behalf of youknowone March 28, 2026 05:38 View session

remove extra_tests/snippets/inspect_getsource.py (covered by test_ins…

2a3d444

…pect) Agent-Logs-Url: https://github.com/RustPython/RustPython/sessions/2b64da1b-8aab-4fec-8b28-3a21d46ac2f9 Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>

Copilot finished work on behalf of youknowone March 28, 2026 05:45

Copilot AI requested a review from youknowone March 28, 2026 05:45

youknowone marked this pull request as ready for review March 28, 2026 15:52

youknowone approved these changes Mar 28, 2026

View reviewed changes

youknowone merged commit 902985d into main Mar 28, 2026
30 of 31 checks passed

youknowone deleted the copilot/fix-inspect-getsource-output branch March 28, 2026 15:52

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Fix `inspect.getsource` returning truncated source for multi-line function definitions#7519

Fix `inspect.getsource` returning truncated source for multi-line function definitions#7519
youknowone merged 4 commits intomainfrom
copilot/fix-inspect-getsource-output

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Root cause

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📦 Library Dependencies

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