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lint rule: hand-rolled-fetch (key? ? h[k] : default pattern) #205

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opened 2026-08-01 14:16:55 +00:00 by jared · 1 comment

jared commented

2026-08-01 14:16:55 +00:00

Owner

Migrated from jared/os-sdlc#31 (repo retired).

Problem

@h.key?(k) ? @h[k] : default

A hand-rolled default-lookup where Hash#fetch already does this. Note: rubocop's own Style/HashFetch is NOT in play here -- this repo's .rubocop.yml sets AllCops: DisabledByDefault: true, so only explicitly-listed cops run, and Style/HashFetch is not among them.

Detection

Inputs: lib/ Ruby source.
Algorithm: custom cop matching the AST pattern h.key?(k) ? h[k] : d (ternary guarded by #key? on the same receiver/key, else-branch a constant/literal), autocorrecting to h.fetch(k, d).
Failure message: "reimplements Hash#fetch via key? ? h[k] : default. Use h.fetch(k, default)."

Correction

Use Hash#fetch with a default: h.fetch(k, default).

Pass/fail examples

Must fail: the ternary h.key?(k) ? h[k] : default pattern.
Must pass: h.fetch(k, default).

Provenance

Fable finding. Run 18 (ticket #18, decision-dice sandbox, now retired), dual review, 2026-07-21.

Implementation plan

Candidate custom cop for plugins/os-sdlc/lib/os_sdlc/cops/ (Sdlc/Structural or Sdlc/Dry namespace); autocorrect-capable like rubocop's own Style cops.

Migrated from jared/os-sdlc#31 (repo retired). ## Problem @h.key?(k) ? @h[k] : default A hand-rolled default-lookup where Hash#fetch already does this. Note: rubocop's own Style/HashFetch is NOT in play here -- this repo's .rubocop.yml sets `AllCops: DisabledByDefault: true`, so only explicitly-listed cops run, and Style/HashFetch is not among them. ## Detection - **Inputs:** lib/ Ruby source. - **Algorithm:** custom cop matching the AST pattern `h.key?(k) ? h[k] : d` (ternary guarded by #key? on the same receiver/key, else-branch a constant/literal), autocorrecting to `h.fetch(k, d)`. - **Failure message:** "reimplements Hash#fetch via key? ? h[k] : default. Use h.fetch(k, default)." ## Correction Use Hash#fetch with a default: `h.fetch(k, default)`. ## Pass/fail examples - **Must fail:** the ternary `h.key?(k) ? h[k] : default` pattern. - **Must pass:** `h.fetch(k, default)`. ## Provenance Fable finding. Run 18 (ticket #18, decision-dice sandbox, now retired), dual review, 2026-07-21. ## Implementation plan Candidate custom cop for plugins/os-sdlc/lib/os_sdlc/cops/ (Sdlc/Structural or Sdlc/Dry namespace); autocorrect-capable like rubocop's own Style cops.

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2026-08-01 14:16:55 +00:00

jared commented

2026-08-01 14:27:16 +00:00

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Implemented Sdlc/Dry/HandRolledFetch cop (lib/os_sdlc/cops/hand_rolled_fetch.rb, tests/cops/hand_rolled_fetch_test.rb, 7 tests incl. autocorrect). Registered in .rubocop.yml. Commit c54593f.

Implemented Sdlc/Dry/HandRolledFetch cop (lib/os_sdlc/cops/hand_rolled_fetch.rb, tests/cops/hand_rolled_fetch_test.rb, 7 tests incl. autocorrect). Registered in .rubocop.yml. Commit c54593f.

jared closed this issue

2026-08-01 14:27:18 +00:00

jared referenced this issue from a commit

2026-08-01 19:14:43 +00:00

os-sdlc: add Sdlc/Dry/HandRolledFetch cop (#205)

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