Centralize CSV/style option parsing

[eitoball]

What

Adds Comma::Options.parse(input) as the single entry point for parsing the to_comma/render csv: style-symbol-or-options-hash argument, and switches Comma::Generator and the Rails csv: renderer to use it.

Why

Comma::Generator#initialize and the Rails renderer in lib/comma.rb each parsed the style-vs-hash argument slightly differently, and the renderer additionally carried a manual # XXX: Convert string to boolean hack for write_headers (needed because Rails params arrive as strings). The duplication meant a Comma-specific option added in one place could silently be missed in the other.

Closes #163.

Changes

• New lib/comma/options.rb: Comma::Options.parse accepts a bare style symbol, a hash of style/filename/CSV options, or nil, and returns { style:, filename:, csv: }. It also owns the write_headers string→boolean coercion.
• lib/comma/generator.rb: Generator#initialize now delegates to Comma::Options.parse instead of inlining the Symbol/Hash branching.
• lib/comma.rb: the Rails :csv renderer's manual write_headers string-coercion block is removed — it now shares the same normalization by routing through Generator via obj.to_comma.
• New spec/comma/options_spec.rb: unit coverage for default/symbol/hash/style/filename/write_headers-coercion/non-mutation behavior.
• .rubocop_todo.yml: added lib/comma/options.rb to the Style/Documentation exclusion, matching every other file under lib/comma/.

No public API changes; existing to_comma/render csv: call sites behave the same.

Test plan

• bundle exec rspec — 55 examples, 0 failures (46 pre-existing + 9 new)
• bundle exec rubocop clean on all changed files
• Rails-matrix controller specs (spec/controllers/users_controller_spec.rb) — not runnable locally (native gem builds for the Rails appraisal gemfiles aren't set up in this environment); relies on CI, and I traced the write_headers string/boolean/combo scenarios by hand against the new code to confirm no behavior change

🤖 Generated with Claude Code

[Copilot]

🟡 Changes recommended

Comma::Options.parse uses clone, which can raise on frozen input hashes, and the new nil→:default normalization changes observable behavior that should be explicitly resolved/aligned.

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Pull request overview

This PR centralizes parsing of the to_comma / Rails render csv: “style symbol vs options hash” argument into a single entry point (Comma::Options.parse) so both Comma::Generator and the Rails CSV renderer share consistent normalization (including write_headers string→boolean coercion).

Changes:

• Add Comma::Options.parse(input) returning normalized { style:, filename:, csv: }.
• Update Comma::Generator#initialize to delegate option parsing to Comma::Options.
• Remove Rails renderer’s bespoke write_headers string coercion and rely on the shared parsing path via obj.to_comma.

File summaries

File	Description
lib/comma/options.rb	Introduces centralized parsing/normalization of style/filename/CSV options (including write_headers coercion).
lib/comma/generator.rb	Switches generator initialization to consume parsed options from Comma::Options.
lib/comma.rb	Loads comma/options and removes duplicated renderer-side coercion logic.
spec/comma/options_spec.rb	Adds unit tests for Comma::Options.parse behavior and non-mutation.
.rubocop_todo.yml	Excludes the new file from Style/Documentation, matching existing lib/comma/* exclusions.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 2
• Review effort level: Lite

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[Copilot]

🔵 Needs a closer look

Comma::Options.parse currently accepts non-Symbol non-Hash inputs (and treats false as “use default”), which can silently mask invalid arguments and should be tightened to the documented contract.

Review details

Suppressed comments (1)

lib/comma/options.rb:13

• Comma::Options.parse currently treats any non-Hash input as a style value (including false, strings, etc.), and false will silently fall back to the default style because of input || .... Since this is intended to be the single entry point for parsing the style-vs-options argument, it should explicitly accept only nil, Symbol, or Hash and raise a clear ArgumentError otherwise; while doing so, use dup instead of clone so parsing doesn’t preserve frozen? state and explode when deleting keys.

    def parse(input)
      return { style: input || Comma::DEFAULT_OPTIONS[:style], filename: nil, csv: {} } unless input.is_a?(Hash)

      csv = input.clone
      style = csv.delete(:style) || Comma::DEFAULT_OPTIONS[:style]
      filename = csv.delete(:filename)
      csv[:write_headers] = csv[:write_headers] != 'false' if csv[:write_headers].is_a?(String)

• Files reviewed: 5/5 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The shared parser preserves existing behavior while reducing duplication, and the new unit specs plus existing controller specs cover the key normalization scenarios (including write_headers).

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0 new
• Review effort level: Lite