Fix phpstan/phpstan#14452: Performance degradation introduced in 2.1.41

[phpstan-bot]

Summary

Fixes a severe performance regression introduced in 2.1.41 where analysis of code with many possibly-impure method calls inside conditional branches could take exponentially longer (from 0.3s to 14+ minutes in the reported case). The regression was caused by PossiblyImpureCallExpr entries participating in the conditional expression system during scope merges, creating O(N^2) conditional expressions that were then repeatedly processed during type narrowing.

Changes

• Modified MutatingScope::createConditionalExpressions() in src/Analyser/MutatingScope.php to skip PossiblyImpureCallExpr entries in three places:
  1. Excluded from the $typeGuards set (prevents O(N^2) conditional expression creation)
  2. Excluded from the $newVariableTypes loop that creates conditional expressions for variables
  3. Excluded from the $mergedExpressionTypes loop that creates ErrorType conditional expressions
• Added regression test tests/PHPStan/Analyser/nsrt/bug-14452.php

Root cause

The commit cf070ae ("Tip about adding @phpstan-impure where applicable") introduced PossiblyImpureCallExpr nodes that are stored in the scope's expression types for every possibly-impure method/function call. These nodes carry the declared return type for use in tip generation.

When an if block contains N possibly-impure method calls, all N PossiblyImpureCallExpr entries become type guards during scope merging in createConditionalExpressions. This creates O(N * M) conditional expressions (where M is the total number of differing expression types, also O(N)), resulting in O(N^2) conditional expressions. These conditional expressions are then processed during every subsequent type narrowing operation in a while-loop fixed-point iteration.

PossiblyImpureCallExpr entries should not participate in the conditional expression system because they store fixed declared return types (metadata for tip generation), not control-flow-dependent types that need narrowing across branches.

Test

The regression test (tests/PHPStan/Analyser/nsrt/bug-14452.php) reproduces the issue pattern from the bug report: a class with many possibly-impure method calls (MyBag::getInt(), MyBag::has(), MyBag::get()) inside conditional branches with nested ifs. Without the fix, the test times out (>60s). With the fix, it completes in ~0.2s.

Fixes phpstan/phpstan#14452

[staabm]

with this fix applied, the "never ending case" from the reproducer in bug 14452 ends in 0.17 seconds.

reason for the slowness were lots of conditional types based on virtual-nodes (possibly-impure-method-call)