Do not propagate isAlwaysTerminating from immediately-invoked callable arguments to the outer call

[phpstan-bot]

Summary

When a closure or arrow function that always terminates (returns never, e.g. fn() => throw new Error()) was passed as an @param-immediately-invoked-callable parameter, PHPStan incorrectly concluded the entire outer function call always terminates. This caused false positive "Unreachable statement" errors on code following the call.

The fix stops propagating isAlwaysTerminating from callback arguments to the outer call in NodeScopeResolver::processArgs(). "Immediately invoked" means the callback runs during the function's execution (not stored for later), but it does NOT guarantee the callback is called on every code path — array_filter only calls the callback per element (empty array = never called), Choice::proceed may call only one of two callbacks, etc.

Changes

• Removed $isAlwaysTerminating propagation in src/Analyser/NodeScopeResolver.php for all three callable argument branches:
  • Closure arguments (was line 3405)
  • ArrowFunction arguments (was line 3465)
  • Other callable expressions like first-class callables (was line 3496)
• Removed now-unused ProcessClosureResult::isAlwaysTerminating() method and $isAlwaysTerminating field from src/Analyser/ProcessClosureResult.php
• Removed unused $isAlwaysTerminating computation in processClosureNode() (was line 2792)
• Updated tests/PHPStan/Analyser/ExpressionResultTest.php expectations for call_user_func(fn() => exit()) and call_user_func(function() { exit(); }) — these are now false (minor false negative, acceptable trade-off)

Root cause

NodeScopeResolver::processArgs() was propagating the isAlwaysTerminating flag from immediately-invoked callback results to the outer function call's ExpressionResult. When any callback argument was always-terminating (returning never), the entire function call was marked as always-terminating. This is incorrect because "immediately invoked" does not mean "always invoked" — the function may only call the callback conditionally.

Three parallel code paths had the same bug:

1. Closure arguments → $closureResult->isAlwaysTerminating()
2. Arrow function arguments → $arrowFunctionResult->isAlwaysTerminating()
3. Non-closure callable arguments → $returnType instanceof NeverType && $returnType->isExplicit()

Throw points and impure points are still correctly propagated (the callback CAN throw, so the function call might throw), only the "always terminates" assertion was wrong.

Analogous cases probed

• FuncCallHandler / MethodCallHandler / StaticCallHandler / NewHandler: These all check the function/method's OWN return type for NeverType, not callback arguments — already correct.
• IIFEs (immediately-invoked function expressions like (fn() => exit())()): These are processed as FuncCall with the closure as the callee expression, not as callback arguments — not affected by this fix.
• @param-later-invoked-callable: callCallbackImmediately() returns false for these, so nothing propagates — already correct.
• set_error_handler / pcntl_signal: Not marked as immediately-invoked — already correct (verified by existing tests bug-13288, bug-13311, bug-13331).

Test

• Added rule test tests/PHPStan/Rules/DeadCode/data/bug-14582.php covering:
  • The original issue's Choice::proceed() pattern with @param-immediately-invoked-callable
  • array_filter with never-returning arrow function
  • array_map with never-returning arrow function
  • usort with never-returning arrow function
  • array_filter with never-returning closure
• Added NSRT test tests/PHPStan/Analyser/nsrt/bug-14582.php verifying type inference works correctly after array_filter/array_map with never-returning callbacks

Fixes phpstan/phpstan#14582