ADR-0008: Member misses on built-in receivers are errors (UNDEFINED_METHOD / UNDEFINED_PROPERTY)

• Status: Accepted
• Date: 2026-07-02

Context

c.casll() on a Callable emitted only the opt-in UNSAFE_METHOD_ACCESS — silent under project defaults — while Godot itself hard-errors (Function "casll()" not found in base Callable). Probed on 4.7 with --check-only: builtin receivers error for methods and properties, typed and :=-inferred alike; Object and script receivers stay silent (a script can attach members at runtime); Dictionary property access is silent for any name, reads and writes (keyed-subscript sugar), while a Dictionary method miss still errors. The TECH_DEBT "closed-builtin receiver severity study" asked exactly this question.

Decision

We will emit UNDEFINED_METHOD / UNDEFINED_PROPERTY (ERROR by default) from builtin_member_ty when a member miss occurs on a built-in receiver. Unlike UNDEFINED_FUNCTION/UNDEFINED_IDENTIFIER (ADR-0005), these need no workspace-completeness claim: the builtin member tables ship with the analyzer and are closed. Gates: a project declaring a newer engine than the bundled model falls back to the opt-in UNSAFE_* (the member may exist there); Nil receivers stay silent (a nullability question, not member existence). Keyed builtins short-circuit the whole property path: d.some_key on a Dictionary is subscript sugar typed as the dictionary's value type, and the key wins even over real method names ({"size": 99}.size is 99 at runtime — probed) — never a diagnostic. A Dictionary method miss still errors: method-call sugar does not dispatch to callable values (d.greet() crashes at runtime even when the key holds a Callable — probed), so flagging it is a true positive. Object and script receivers keep the opt-in UNSAFE_* (Godot parity).

Consequences

Easier: the .casll() class of typo is a default-on error with a precise squiggle — including Godot-3→4 renames (upper() vs to_upper()) — and dict.key now types as the value type instead of Variant. Harder: strict-mode users lose the (false) UNSAFE_PROPERTY_ACCESS they previously saw on Dictionary keyed access — that was a pre-existing false positive, now fixed; and a project on a newer engine gets the weaker opt-in signal for genuinely-new members, by design. Corpus proof: the first run surfaced 111 UNDEFINED_PROPERTY hits across 138 godot-demo-projects — all of them the Dictionary sugar shape — and zero after the keyed short-circuit; zero UNDEFINED_METHOD false positives throughout.

Addendum (2026-07-03 — T4.1 message parity)

Godot 4.7 prints two lines for one builtin method miss — Cannot find member "casll" in base "Callable". (its member check) and Function "casll()" not found in base Callable. (its call check) — and only the member line for a property miss; a Dictionary method miss gets only the call line (the keyed sugar absorbs the member check). Earlier notes each quoted ONE of the two as "the" native phrasing and looked contradictory — both were real. The analyzer emits one diagnostic per site and mirrors the kind-matching text verbatim: the call-check wording for UNDEFINED_METHOD, the member wording for UNDEFINED_PROPERTY. The golden table (crates/gdscript-hir/src/godot_messages_tests.rs) pins both against the probed binary.