[fix] Crash when parsing an empty arbitrary expression with extract_node

[Pierre-Sassoulas]

Type of Changes

	Type
✓	🐛 Bug fix

Description

To be fair I'm not exactly sure of what the transient function is. It seems internal. But the fix seems self evident.

astroid/astroid/builder.py

Lines 32 to 35 in 3636bc2

	# The name of the transient function that is used to
	# wrap expressions to be extracted when calling
	# extract_node.
	_TRANSIENT_FUNCTION = "__"

astroid/astroid/builder.py

Lines 303 to 315 in 3636bc2

	def _extract_expressions(node: nodes.NodeNG) -> Iterator[nodes.NodeNG]:
	"""Find expressions in a call to _TRANSIENT_FUNCTION and extract them.
	The function walks the AST recursively to search for expressions that
	are wrapped into a call to _TRANSIENT_FUNCTION. If it finds such an
	expression, it completely removes the function call node from the tree,
	replacing it by the wrapped expression inside the parent.
	:param node: An astroid node.
	:type node: astroid.bases.NodeNG
	:yields: The sequence of wrapped expressions on the modified tree
	expression can be found.
	"""

astroid/astroid/builder.py

Lines 324 to 328 in 3636bc2

	# Search for node in all _astng_fields (the fields checked when
	# get_children is called) of its parent. Some of those fields may
	# be lists or tuples, in which case the elements need to be checked.
	# When we find it, replace it by real_expr, so that the AST looks
	# like no call to _TRANSIENT_FUNCTION ever took place.

Closes #2734

[DanielNoord]

If CI approves I approve as well :)

[Pierre-Sassoulas]

Do you understand the transient function though ? 😄

[DanielNoord]

See b8dc84f

It seems to be a very bespoke way to do extraction of nodes in extract_node.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.21%. Comparing base (3636bc2) to head (e401578).
⚠️ Report is 58 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2736   +/-   ##
=======================================
  Coverage   93.21%   93.21%           
=======================================
  Files          93       93           
  Lines       11072    11072           
=======================================
  Hits        10321    10321           
  Misses        751      751           

Flag	Coverage Δ
linux	93.08% <ø> (ø)
pypy	93.21% <ø> (ø)
windows	93.19% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
astroid/builder.py	95.13% <ø> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Pierre-Sassoulas]

Ha, thank you, here's the doc:

     To extract arbitrary expressions, surround them with the fake
     function call __(...). After parsing, the surrounded expression
     will be returned and the whole AST (accessible via the returned
     node's parent attribute) will look like the function call was
     never there in the first place.

     Examples:

       >>> a = __(1)

       The const node will be extracted.

       >>> def x(d=__(foo.bar)): pass

       The node containing the default argument will be extracted.

       >>> def foo(a, b):
       >>>   return 0 < __(len(a)) < b

       The node containing the function call 'len' will be extracted.

    If no statements or expressions are selected, the last toplevel
    statement will be returned.
    If the selected statement is a discard statement, (i.e. an expression
    turned into a statement), the wrapped expression is returned instead.

I'm going to update the changelog then. Learned something today.

[DanielNoord]

I'm going to update the changelog then. Learned something today.

Don't we all when we look at astroid 😄

[Pierre-Sassoulas]

Yeah, great piece of software, feels awesome.