Fix type: [A, B] + values: [...] raising IncompatibleOptionValues at definition time

[ericproulx]

Summary

Sibling of #2812 (fixed by #2813): a multiple-type declaration combined with values: or except_values: raises Grape::Exceptions::IncompatibleOptionValues at definition time on master, so the API class fails to load. All of these were accepted in 3.2.1 (verified against the v3.2.1 tag):

Declaration	3.2.1	master (before this PR)
type: [Integer, String], values: [1, 2]	OK	raises at definition time
type: [Integer, String], except_values: [3]	OK	raises at definition time
type: Set[Integer, String], values: [1]	OK	raises at definition time
types: [Integer, String], values: [1]	OK	OK (raw-list path, unaffected)

The raised message even has a blank type name (type: is incompatible with values: [1, 2]), which hints at the root cause below.

Root cause

Same clobbering family as #2812. ValidationsSpec#parse_coerce stores a Types::VariantCollectionCoercer instance in @coerce_type when Types.multiple?(type) is true — correct for runtime coercion and for documentation (to_s → "Array[Integer, String]"), but the definition-time coherence check also reads @coerce_type:

value_types.all?(coerce_type)  # all? with a pattern uses ===

VariantCollectionCoercer doesn't define ===, so Object#=== (identity) matches nothing and the check can never pass.

In 3.2.1 the two roles were separate: infer_coercion returned the raw declared type ([Integer, String]) for validate_value_coercion/guess_coerce_type/docs, while the wrapper went into validations[:coerce] for the runtime validator. The ValidationsSpec refactor merged both roles into @coerce_type; #2813 un-merged the values-guessed-type leg but not this one.

Fix

Mirrors #2813's isolation strategy:

• ValidationsSpec gains a private declared_coerce_type that unwraps a VariantCollectionCoercer back to the declared member-type list, and guess_coerce_type/validate_value_coercion now receive that. @coerce_type is untouched, so coerce_options (runtime) and ParamsDocumentation (renders "Array[Integer, String]") keep their current behavior.
• VariantCollectionCoercer gains an attr_reader :types so the declared list is recoverable from the wrapper.

The restored check semantics are exactly 3.2.1's: the declared list is Enumerable, so the existing coerce_type = coerce_type.first if coerce_type.is_a?(Enumerable) line validates values against the first declared member type. That means type: [Integer, String], values: %w[active] still raises — quirky, but it is the historical contract, and this PR deliberately restores rather than redesigns it.

Tests

• spec/grape/validations/params_scope_spec.rb: six integration cases — values:, except_values:, and Set[...] accepted at definition time; array of allowed values accepted at request time; disallowed value rejected with does not have a valid value; incompatible values list still raises IncompatibleOptionValues.
• spec/grape/validations/validations_spec_spec.rb: unit coverage that the wrapper stays in coerce_type while the values check passes, and that an incompatible list still raises.

Full suite: 2375 examples, 0 failures. RuboCop clean.

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