[ty] Simplify mapped intersections through aliases

[charliermarsh]

Summary

Builds on #29152.

We now simplify mapped intersections through aliases without expanding the alias unless a simplification changes the result. For example:

from typing import Literal
from ty_extensions import Intersection, Not

type Minus[T, U] = Intersection[T, Not[U]]
type Boolean = bool
type TrueLiteral = Literal[True]

def f(x: Minus[Boolean, TrueLiteral]):
    reveal_type(x)  # Literal[False]

Previously, we revealed Boolean & ~Literal[True]. The alias was retained to avoid unfolding recursive types, but that hid the boolean from the normal simplification rule.

Intersection construction still expands unions, nested intersections, and enum complements so it can distribute and flatten them. The inner builder now inspects the underlying types when applying simplification rules, including truthiness, enum exclusions, constrained type variables, and gradual generics. Unchanged aliases retain their identity. This removes the separate lists of positive and negated alias shapes that could be preserved.

[astral-sh-bot]

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 98.24%. The percentage of expected errors that received a diagnostic held steady at 98.24%. The number of fully passing files held steady at 134/146.

[astral-sh-bot]

Memory usage report

Memory usage unchanged ✅

[astral-sh-bot]

ecosystem-analyzer results

No diagnostic changes detected ✅

Full report with detailed diff (timing results)

[codspeed]

Merging this PR will degrade performance by 7.58%

❌ 6 regressed benchmarks
✅ 156 untouched benchmarks
⏩ 74 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	auto_imports[regular-package/after-module-create]	22.5 ms	25.7 ms	-12.73%
❌	WallTime	auto_imports[namespace-package/after-module-create]	26 ms	29.2 ms	-10.87%
❌	Simulation	ty_micro[pandas_tdd]	904.6 ms	992.7 ms	-8.87%
❌	Simulation	attrs (frozen inputs)	1.3 s	1.4 s	-4.38%
❌	Simulation	attrs	1.4 s	1.5 s	-4.19%
❌	Simulation	attrs (all rules)	1.4 s	1.5 s	-4.06%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing charlie/ty-alias-aware-intersections (df4f9a4) with charlie/ty-shared-recursion-guards (bca1de0)}

Footnotes

1. 74 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩