Stops Meta claiming methods it has no value for

[ehannes]

Meta#respond_to_missing? returned true for every name, on the reasoning that method_missing answers to everything so respond_to? should agree. That is internally consistent but wrong: the set of names Ruby asks about is far larger than the set anyone will ever call. Every implicit probe got a false yes and then took the nil that method_missing returns for an unknown key as a real answer.

Marshal made it expensive. dump asked for marshal_dump, got nil, and wrote that as the object's entire serialised state — 20 bytes, no error. load then called marshal_load on an allocated instance with no @DaTa yet, raising

NoMethodError: undefined method `[]' for nil:NilClass

from inside method_missing. Consumers caching resources in a store that marshals its entries wrote a poisoned entry on the first request and raised on every cache hit after that. Found via fortnox-api on a Rails :memory_store, where every resource carries a Meta and the second request inside the cache window blew up.

Bare getters are now whitelisted against the keys @DaTa actually holds — the same shape ModelProxy already uses for model attributes. Setters and predicates stay unconditional: writing is how a key comes into existence and an unset predicate is meaningfully false. A blacklist of protocol names was considered and rejected; it cannot be enumerated, which is the tell that it was the wrong shape.

Three details the first cut of this fix got wrong:

• @DaTa is guarded, because respond_to? must never raise and Ruby allocates before initialising. Psych's revive probes init_with on a bare allocation, and so does Marshal.load on a payload written by an older version. Without the guard the whitelist merely moved the NoMethodError out of method_missing and into respond_to_missing?. With it, YAML round-trips — which it never did before — and a stale payload fails as a legible TypeError.

• The name check is anchored to /\A[a-zA-Z_]\w*[=?]\z/ rather than end_with?("="), so operators stay out. Unanchored, respond_to?(:<=) was true and meta <= 5 read as a setter writing @DaTa[:<]. Only half the hole: Ruby dispatches operators without consulting respond_to?, so method_missing still writes that key. Filed as Meta#method_missing treats operators as setters #6.

• The guarantee is narrower than "nothing probes for = or ?". No core Ruby probe uses those shapes, but ActiveSupport's acts_like?(:date) is respond_to?(:acts_like_date?), so Meta still answers yes. Filed as 2.0: Reconcile Meta's two halves by declaring meta keys up front #7 rather than papered over.

Resource::MetaCollector had the identical defect and gets the identical treatment, guard and anchoring included.

method_missing is deliberately unchanged. A bare getter for an unset key still returns nil rather than raising, because the gem author extensions example in docs/model-architecture.md sets a meta key conditionally and reads it unconditionally; raising would break it on every full resource. respond_to? therefore under-reports for never-set keys, which is the safe direction — Ruby's implicit probes consult respond_to? and so never reach method_missing. Reconciling the two halves means requiring meta keys to be declared up front, which closes the acts_like? and operator holes with it; filed as #7 for 2.0.

Payloads written before this fix are not recoverable, so the CHANGELOG carries an upgrade note for consumers on a cache that survives deploys.

Adds spec/rest_easy/meta_spec.rb plus MetaCollector coverage in resource_spec.rb — 26 examples, 16 of which fail against the unfixed code. Covers both constructor paths for meta (class-level metadata defaults and before_parse hooks), collections, stubs, YAML, and a whole-hash assertion, since the original failure nulled @DaTa entirely and spot-checking single keys would have been weak. The implicit coercion examples assert on the TypeError message rather than its class: both versions raise, and only the broken one reports "#to_hash gives NilClass".

[Copilot]

Pull request overview

Prevents Meta and MetaCollector from claiming unsupported methods, fixing serialization and coercion failures.

Changes:

• Restricts dynamic method introspection to known getters and valid accessors.
• Adds Marshal, YAML, coercion, and metadata regression coverage.
• Documents behavior and cache migration requirements.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
lib/rest_easy/meta.rb	Refines dynamic method introspection.
lib/rest_easy/resource.rb	Applies equivalent handling to MetaCollector.
spec/rest_easy/meta_spec.rb	Adds serialization and coercion regression tests.
spec/rest_easy/resource_spec.rb	Adds MetaCollector coverage.
CHANGELOG.md	Documents the fix and upgrade guidance.

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