fix: call mark_as_used() for classes referenced only in instanceof (#68)

[KorsarOfficial]

Problem

When a class C appears only in an instanceof expression and is never instantiated or used as a value, the code-gen pass crashes: it emits an #include for C's header, but the header was never generated because mark_as_used() was never called for C.

Formal Analysis

Define the class dependency system:

• Let C = {c₁, c₂, …, cₙ} — set of all classes
• U(c) — predicate: class is marked as "used"
• H(c) — predicate: header file was generated
• R(c) — predicate: class is referenced in code-gen output

Code-gen invariant: ∀c ∈ C : R(c) ⟹ H(c)
Header rule: H(c) ⟺ U(c)
Required invariant: ∀c ∈ C : R(c) ⟹ U(c)

The existing mark_as_used() calls cover instantiation, catch, type hints, and value references — but not instanceof. When instanceof is the only reference, U(c) = false while R(c) = true, violating the invariant.

Fix

Add mark_as_used() for op_instanceof in CalcFuncDepPass::on_enter_vertex, mirroring the identical pattern for op_catch.

Correctness: U'(c) = U(c) ∨ instanceof_ref(c) ⟹ ∀c : R(c) ⟹ U'(c) ⟹ H(c). ∎

Complexity: O(1) per instanceof vertex — negligible overhead.

Tests

• tests/phpt/interfaces/135_instanceof_unused_class.php — basic regression
• tests/phpt/interfaces/136_instanceof_only_in_condition.php — instanceof only in conditional branch

Technical Report

📄 Full report with mathematical formalization (PDF)

Closes #68

[Danil42Russia]

Why open a new thread when there’s already #1557? Apart from the fact that you’ve removed the use of Claude

[KorsarOfficial]

Hey, fair point. I've been experimenting with Claude as a coding assistant recently — it ended up as a co-author in the commits by default, and I didn't notice until after the PRs were already up. Didn't want that showing up in upstream history, so I cleaned it up and reopened. Sorry for the noise.

The code changes are the same, just without the AI attribution in the commit metadata.