Add RuboCop cop enforcing Data.define over Struct.new - #2879
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Requested in review on PR #2855: prefer Data.define over Struct.new for immutable value objects. The custom cop flags Struct.new sends without autocorrection (mutability and keyword semantics differ, so each hit needs a human decision) and is required from .rubocop.yml. Converts the seven Struct.new test doubles in spec/helpers/email_header_helper_spec.rb to Data.define — the only usages in the repo. Data.define accepts the same positional arguments here. Refs #2878
CI eager-loads the app (config.eager_load = ENV['CI'].present? in test.rb), and autoload_lib walked lib/rubocop, requiring the cop before rubocop was loaded: 'uninitialized constant RuboCop::Cop::Style::Base'. RuboCop cops are loaded by RuboCop itself via the require in .rubocop.yml, not by Rails; exclude the directory from autoloading, as the autoload_lib comment invites.
mroderick
marked this pull request as ready for review
September 15, 2026 10:46
olleolleolle
approved these changes
Sep 15, 2026
Review feedback on #2879: the spec's member stand-ins should be RSpec doubles rather than Data.define instances. instance_double(Member) verifies against the real class and satisfies RSpec/VerifiedDoubles. The helper only reads member.id and member.email.
mroderick
enabled auto-merge
September 15, 2026 15:17
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Closes #2878.
Adds a custom RuboCop cop,
Style/PreferDataDefine, that flagsStruct.newsends with no autocorrection. The sevenStruct.newtest doubles inspec/helpers/email_header_helper_spec.rbare now RSpec verifying doubles (instance_double(Member, ...)), per review feedback — the repo's onlyStruct.newusages are gone. Follows Olle's review request on #2855.The cop is required from
.rubocop.yml, sobundle exec rubocopand CI enforce the preference from now on. A review round also fixed Zeitwerk eager-loading oflib/rubocopunder CI. No autocorrection on purpose: theStruct.new->Data.definerewrite isn't safely mechanical (mutability and keyword semantics differ), so each future hit gets a human decision.Review notes
ConstNode#valueno longer exists in rubocop-ast 1.50, the cop usesconst_name == 'Struct'instead (verified for bothStructand::Struct; namespaced receivers likeOther::Struct.neware correctly ignored).AllCops.Exclude(db/config/bin) is not covered; a future--regenerate-todowhile offenses exist would add a todo entry and suppress the cop; name-based indirection (s = Struct; s.new) bypasses it.