Support boolean truthiness constraints in inference

[zenlyj]

Type of Changes

	Type
	🐛 Bug fix
✓	✨ New feature
	🔨 Refactoring
	📜 Docs

Description

This PR builds on #1189 by implementing the constraint interface to handle boolean constraints, similar to how None constraints are currently treated.

Previously, constraints only accounted for None checks:

x = 1

if x is None:
    x    # Uninferable, `1` is filtered out because x is not None

These changes support constraints derived from boolean truthiness:

1. If condition is True, keep the inferred value.

x = 1    # truthy

if x:
    x    # inferred as `1`

2. If condition is False, filter out the inferred value.

x = []    # falsy

if x:
    x    # Uninferable, `[]` filtered out

3. Negation rules are the same as None constraints.

x = 1

if x:
    pass
else:
    x    # Uninferable, `1` filtered out


y = []

if not y:
    y    # inferred as `[]`

4. If the boolean value cannot be inferred, assume constraint is satisfied.

Closes pylint-dev/pylint#9515

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.35%. Comparing base (90188b4) to head (04eb2cb).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2823   +/-   ##
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  Coverage   93.35%   93.35%           
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  Files          91       91           
  Lines       11100    11113   +13     
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+ Hits        10362    10375   +13     
  Misses        738      738           

Flag	Coverage Δ
linux	93.22% <100.00%> (+<0.01%)	⬆️
pypy	93.35% <100.00%> (+<0.01%)	⬆️
windows	93.34% <100.00%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
astroid/constraint.py	100.00% <100.00%> (ø)

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[Pierre-Sassoulas]

Looks amazing !

[DanielNoord]

Perhaps we should add a Changelog entry? Rest LGTM!

[jacobtylerwalls]

Lovely, I'm glad more knowledge of the constraints interface is starting to spread 🪐

[zenlyj]

Thanks for the reviews! A lot of thought and effort went into the constraints interface, and it deserves to be built upon rather than left unused. More extensions coming soon in separate PRs!