Treat first-class callable NullsafeMethodCall as a MethodCall instead of throwing

[phpstan-bot]

Summary

Using the first-class callable syntax together with the nullsafe operator
($foo?->bar(...)) crashed PHPStan with Internal error.. While this is a
fatal error in PHP itself ("Cannot combine nullsafe operator with Closure
creation"), PHPStan must not crash on it. This change makes the analyser treat
such an expression as a regular method-call first-class callable.

Changes

• src/Analyser/NodeScopeResolver.php: in the first-class callable branch of
  processExprNode(), handle Expr\NullsafeMethodCall by building a
  MethodCallableNode from an equivalent MethodCall, instead of falling
  through to the throw new ShouldNotHappenException().
• tests/PHPStan/Analyser/nsrt/bug-9746.php: regression test asserting the
  inferred types and (implicitly) that no internal error is thrown.

Root cause

processExprNode() enumerated the Expr\CallLike subclasses that support the
first-class callable syntax — FuncCall, MethodCall, StaticCall, New_ —
and threw ShouldNotHappenException for anything else. NullsafeMethodCall is
also an Expr\CallLike whose isFirstClassCallable() can be true (the parser
accepts $foo?->bar(...) even though PHP rejects it at runtime), so it hit the
else branch and crashed. It was the only Expr\CallLike subclass not covered.

Test

• tests/PHPStan/Analyser/nsrt/bug-9746.php reproduces the original crash via
  $foo?->doFoo(...) (nullable and non-nullable receivers, plus an assignment)
  and asserts (Closure(): int)|null / Closure(): int. It errors with an
  internal error before the fix and passes after.
• Verified manually that the expression no longer crashes in any context
  (statement, assignment, call argument, array element, return).

Analogous cases probed

• The other first-class callable Expr\CallLike subclasses (FuncCall,
  MethodCall, StaticCall, New_) were already handled; NullsafeMethodCall
  was the only missing one.
• MutatingScope::getKeepVoidType() already lists NullsafeMethodCall in its
  first-class-callable guard, and type resolution flows through
  NullsafeMethodCallHandler, so no internal error occurs when the expression
  is typed.

Fixes phpstan/phpstan#9746

[staabm]

Crash bug fixes need a AnalyserIntegrationTest

[phpstan-bot]

Done. I addressed staabm's review by adding the requested AnalyserIntegrationTest coverage for the crash fix.

What I did

1. New data file tests/PHPStan/Analyser/data/bug-9746.php — reproduces the original crash path (the first-class callable NullsafeMethodCall used as a statement, which is exactly what hit CallToMethodStatementWithoutSideEffectsRule → MutatingScope::resolveType() → ShouldNotHappenException in the issue's stack trace).

2. New test testBug9746() in AnalyserIntegrationTest — runs the full analyser over the file and asserts the three resulting errors, confirming analysis completes without an internal error.

Verification

• With the fix: test passes (10 assertions).
• Without the fix (temporarily reverted the committed NullsafeMethodCall branch): the test errors with the ShouldNotHappenException internal error — confirming it genuinely catches the crash.
• make phpstan: No errors.

Committed as a2149b421 and pushed to create-pull-request/patch-3pnp41f. The existing nsrt/bug-9746.php type-inference test remains as-is; this adds the integration-level crash regression the reviewer asked for.