Emit virtual Assign node for List_ destructuring in foreach value position

[phpstan-bot]

Summary

When array destructuring is used in the foreach value position (e.g. foreach ($arr as ['b' => $val])), PHPStan did not report nonexistent offsets. The same destructuring via regular assignment (['b' => $val] = $arr[0]) or assignment inside the foreach body (['b' => $val] = $item) correctly reported errors.

Changes

• src/Analyser/NodeScopeResolver.php: In the foreach handling code, added emission of a virtual Assign node when $stmt->valueVar is a List_. This is placed alongside the existing VariableAssignNode emission (before the loop convergence iterations) to avoid duplicate reports. The virtual node pairs the List_ with a GetIterableValueTypeExpr so ArrayDestructuringRule can resolve the iterable value type and check offset existence.

• tests/PHPStan/Rules/Arrays/ArrayDestructuringRuleTest.php: Added testBug8075 test method.

• tests/PHPStan/Rules/Arrays/data/bug-8075.php: Regression test data covering:

  • Basic foreach destructuring with nonexistent key
  • Mixed existent/nonexistent keys in foreach
  • PHPDoc-typed arrays with named keys
  • Numeric offset destructuring (tuples)
  • Nested array destructuring in foreach

Root cause

ArrayDestructuringRule is registered as Rule<Assign> — it only fires when the node callback receives an Assign node. For regular assignments like ['b' => $val] = $expr, the parser produces an Assign(List_, expr) which the rule catches. But for foreach ($arr as ['b' => $val]), the parser produces a Foreach_ node with valueVar = List_, and NodeScopeResolver::enterForeach called processVirtualAssign to handle scope updates without ever emitting an Assign node for rules to process.

Analogous cases probed

• Foreach key destructuring: Not valid PHP syntax — keys must be simple variables
• list() vs [] syntax: Both produce List_ AST nodes — handled by the same fix
• Regular assignment destructuring: Already worked correctly (tested in regression test)
• Assignment inside foreach body: Already worked correctly (tested in regression test)
• Nested destructuring: ArrayDestructuringRule::getErrors() already recurses for nested List_ nodes — works with the fix
• Other rules listening for Assign: Only ArrayDestructuringRule does — no unintended side effects

Test

Regression test testBug8075 in ArrayDestructuringRuleTest covers the reported bug and several variations: string keys, integer keys, PHPDoc-typed arrays, nested destructuring, and mixed existent/nonexistent keys.

Fixes phpstan/phpstan#8075