Make $this available as object in non-static closures and arrow functions outside class context

[phpstan-bot]

Summary

When a closure using $this was created outside a class context and stored in a variable, PHPStan reported "Undefined variable: $this" at the definition site. However, closures passed inline to Closure::bind() worked correctly because PHPStan already handled that case specially via StaticCallHandler. This fix makes $this available with type object inside all non-static closures and arrow functions, even outside class context, since Closure::bind() can bind $this to any closure at runtime.

Changes

• src/Analyser/MutatingScope.php:

  • enterAnonymousFunctionWithoutReflection(): Added an elseif branch that sets $this to ObjectWithoutClassType when the closure is non-static, the enclosing scope lacks $this, and we are not inside a Closure::bind() call (checked via isInClosureBind())
  • enterArrowFunctionWithoutReflection(): Same fix for arrow functions — add $this as object when the arrow function is non-static, the parent scope lacks $this, and we are not in a closure bind scope
  • restoreThis(): Added an elseif branch to preserve $this from the restore scope when not in a class but $this is defined. Previously the else branch unconditionally removed $this when isInClass() was false, which caused $this to disappear after processing closure arguments with @param-closure-this annotations inside non-class closures
  • Added use PHPStan\Type\ObjectWithoutClassType import

• Updated test expectations in:

  • tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php: Removed expected error for $this in non-static closure outside class (line 26 of this.php)
  • tests/PHPStan/Analyser/nsrt/param-closure-this.php: Changed *ERROR* to object for $this in non-static closures outside class context
  • tests/PHPStan/Rules/Debug/DebugScopeRuleTest.php: Added $this (Yes): object to expected scope output for closures outside class

Root cause

MutatingScope::enterAnonymousFunctionWithoutReflection() only copied $this into the closure scope when the enclosing scope had $this defined (i.e. inside a class). Non-static closures outside a class never received $this, even though PHP allows $this in such closures when they are later bound via Closure::bind(). The inline Closure::bind() case worked because StaticCallHandler created a special closureBindScope with $this already set before entering the closure.

A secondary issue was that restoreThis() unconditionally removed $this when the restore scope was not in a class, which caused $this (now set to object by the fix) to be lost after processing method calls with @param-closure-this annotations.

Analogous cases probed

• Arrow functions: Same bug existed — fixed in enterArrowFunctionWithoutReflection() with the same approach
• Static closures/arrow functions: Correctly remain without $this — no fix needed, verified with tests
• Closure::bind() with null target: Correctly does NOT add $this — the isInClosureBind() guard prevents the new elseif from firing in bind scopes
• @param-closure-this interaction: Fixed via restoreThis() change — $this is now properly preserved after processing closure arguments with this annotation

Test

• Rule test (tests/PHPStan/Rules/Variables/data/bug-1348.php): Tests that non-static closures and arrow functions outside class context do NOT report "Undefined variable: $this", while static closures/arrow functions still do
• Type inference test (tests/PHPStan/Analyser/nsrt/bug-1348.php): Verifies $this has type object in closures outside class, $this(ClassName) inside class closures, and specific bound type inside inline Closure::bind()

Fixes phpstan/phpstan#1348