Add Readability.SpecParameterNames check

[johnnyt]

Adds a new readability check that flags @spec and @callback parameters which omit the name :: type naming syntax.

Discussed and approved in rrrene/credo-proposals#108 (default-on per maintainer preference).

Behavior

🛑 Reported:

@spec create_user(map(), String.t()) :: {:ok, User.t()}
@callback handle_event(String.t(), map(), Socket.t()) :: {:noreply, Socket.t()}

✅ Not reported:

@spec create_user(attrs :: map(), email :: String.t()) :: {:ok, User.t()}
@callback handle_event(event :: String.t(), params :: map(), socket :: Socket.t()) :: {:noreply, Socket.t()}

Handles:

• Both @spec and @callback
• Guard-style specs (@spec foo(x) :: x when x: term())
• Zero-arity specs (never flagged)
• Remote types (Module.t())
• Multiple specs per module

Details

• Module: Credo.Check.Readability.SpecParameterNames
• Check ID: EX3037
• Category: Readability
• Priority: :low — matches the "documentation-adjacent" tier alongside checks like Readability.Specs
• Default: enabled in .credo.exs (per maintainer steer in the proposal)
• No params — kept minimal for an initial review; happy to add ignore_callbacks or similar if requested

Changes

• lib/credo/check/readability/spec_parameter_names.ex — the check (~100 LOC, AST prewalk)
• test/credo/check/readability/spec_parameter_names_test.exs — 11 tests covering the cases above
• .credo.exs — register the check in the enabled Readability block (alphabetical)
• CHANGELOG.md — entry under 1.7.18

Verification

• mix test test/credo/check/readability/spec_parameter_names_test.exs — 11 tests, 0 failures
• mix credo explain Credo.Check.Readability.SpecParameterNames renders correctly
• The 3 pre-existing failures in MissingCheckInConfigTest / DeprecatedChecksConfigTest exist on a clean master checkout and are unrelated

Origin

I've been running an in-tree copy of this check on a Phoenix codebase for a while. Porting it upstream so other projects can benefit and so the implementation gets community review.

Closes rrrene/credo-proposals#108.

[rrrene]

Hi, I merged this on the command line, but this PR did not close automagically 🤫