Instantiate validators at definition time

[ericproulx]

Summary

Validators are now instantiated once at route definition time rather than per-request via ValidatorFactory. This eliminates repeated object allocation on every request and moves expensive setup (option parsing, converter building, message formatting) out of the hot path.

Because validator instances are shared across all concurrent requests they are frozen after initialization, enforced by a Validators::Base.new override that calls freeze_state! then freeze. A new Grape::Util::DeepFreeze helper recursively freezes Hash/Array/String values while intentionally leaving Procs, coercers, and other mutable objects unfrozen.

Changes

Core

• ParamsScope#validate instantiates the validator class directly and stores the instance in namespace_stackable[:validations]; removes ValidatorFactory
• Endpoint#run_validators reads validator instances directly from saved_validations and removes the validations enumerator method
• ParamsScope is frozen at the end of initialize; element, parent, and Attr#key/Attr#scope changed from attr_accessor to attr_reader
• coerce_type now receives only the extracted coercion keys so callers don't need to delete them afterwards

Validators::Base

• Base.new calls private freeze_state! (deep-freezes all ivars) then freeze; subclasses can override freeze_state! to skip specific ivars
• fail_fast? promoted to explicit public method
• validate_param! promoted to protected with a NotImplementedError default
• hash_like? extracted as a private helper

Grape::Util::DeepFreeze

• New module with a single deep_freeze(obj) function
• Freezes Hash (keys + values), Array (elements), and String recursively
• Returns all other types (Proc, Class, coercers, etc.) untouched

Validator-level eager initialization

• AllowBlankValidator: caches @value and @exception_message
• CoerceValidator: resolves type and builds converter at definition time; overrides freeze_state! to leave the coercer unfrozen
• DefaultValidator: pre-builds @default_call lambda
• ExceptValuesValidator / ValuesValidator: validates proc arity at init
• RegexpValidator, SameAsValidator, PresenceValidator: cache messages
• AllOrNoneOf, AtLeastOneOf, MutuallyExclusiveValidator, ExactlyOneOfValidator: cache exception messages
• ContractScopeValidator: no longer inherits from Base

Specs

• New DeepFreezeSpec
• New specs for SameAsValidator and ExceptValuesValidator
• ContractScopeValidatorSpec / custom_validations_spec updated for the new instantiation model

Test plan

• bundle exec rspec
• Verify no regressions in validation behaviour
• Confirm frozen validator instances raise FrozenError on any attempt to mutate state at request time

[github-actions]

Danger Report

No issues found.

View run

[ericproulx]

Missing UPGRADING notes. Working on it

[dblock]

Is there a tradeoff with things like @exception_message = message(:all_or_none) being always allocated? can they become class variables?

[ericproulx]

Is there a tradeoff with things like @exception_message = message(:all_or_none) being always allocated? can they become class variables?
message involves @option so it can't be a class variable.