Fix Elixir 1.20 type-checker warnings

CHANGELOG.md

@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.2.1] - 2026-06-16
+
+### Fixed
+
+- Elixir 1.20 compatibility. The generated struct `channel/2` no longer trips the new type
+  checker's "redundant clause" warning in consuming applications, and
+  `Amplified.PubSub.Protocol` no longer uses a deprecated default argument in its `channel`
+  definition. No behaviour change.
+
 ## [0.2.0] - 2026-03-20
 
 ### Added

lib/amplified/pubsub.ex

@@ -462,19 +462,28 @@ defmodule Amplified.PubSub do
           subject
         end
 
-        # Default channel: derives from module name + struct id
+        # Default channel: derives from module name + struct id. A struct without an `:id`
+        # field falls through to `nil` and should override `channel/2` (see moduledoc).
+        #
+        # The `:id` check uses `Map.has_key?/2` (a plain call) inside a single clause rather than a
+        # `%module{id: id}` pattern or an `is_map_key/2` guard plus a `_` fallback. Each generated
+        # impl is `for:` a single struct, so the Elixir 1.20+ type checker narrows both the pattern
+        # and the guard to statically cover every value, flagging the `nil` fallback as redundant.
+        # A plain function call is opaque to the checker, keeping the `nil` branch reachable.
         def channel(subject, ns \\ nil)
 
-        def channel(%module{id: id}, ns) do
-          module
-          |> Module.split()
-          |> List.last()
-          |> Recase.to_snake()
-          |> then(&PubSub.channel("#{&1}:#{id}", ns))
+        def channel(%module{} = subject, ns) do
+          if Map.has_key?(subject, :id) do
+            module
+            |> Module.split()
+            |> List.last()
+            |> Recase.to_snake()
+            |> then(&PubSub.channel("#{&1}:#{Map.fetch!(subject, :id)}", ns))
+          else
+            nil
+          end
         end
 
-        def channel(_subject, _ns), do: nil
-
         # Default subscribe/unsubscribe: delegates via channel
         def subscribe(subject) do
           subject |> channel() |> PubSub.subscribe()

lib/amplified/pubsub/protocol.ex

@@ -80,11 +80,17 @@ defprotocol Amplified.PubSub.Protocol do
   e.g. `"post:abc-123"`. The optional `namespace` is appended with a `:`
   separator.
   """
+  @spec channel(subject :: struct()) :: binary()
+  def channel(subject)
+
+  @doc """
+  Returns the PubSub channel name for the given subject, scoped to `namespace`.
+  """
   @spec channel(
           subject :: struct(),
           namespace :: String.t() | atom() | nil
         ) :: binary()
-  def channel(subject, namespace \\ nil)
+  def channel(subject, namespace)
 
   @doc """
   Subscribes the current process to the PubSub channel for the given subject.

lib/amplified/pubsub/tuple.ex

@@ -63,7 +63,7 @@ defimpl Amplified.PubSub.Protocol, for: Tuple do
   def broadcast(error, _message), do: error
   def broadcast({:ok, subject}, event, attrs), do: {:ok, PubSub.broadcast(subject, event, attrs)}
   def broadcast(error, _message, _attrs), do: error
-  def channel(tuple, _ns), do: raise("No channel for #{inspect(tuple)}")
+  def channel(tuple, _ns \\ nil), do: raise("No channel for #{inspect(tuple)}")
   def subscribe(tuple), do: raise("Cannot subscribe to #{inspect(tuple)}")
   def unsubscribe(tuple), do: raise("Cannot unsubscribe from #{inspect(tuple)}")
 

mix.exs

@@ -1,7 +1,7 @@
 defmodule Amplified.PubSub.MixProject do
   use Mix.Project
 
-  @version "0.2.0"
+  @version "0.2.1"
   @source_url "https://github.com/amplifiedai/amplified_pubsub"
 
   def project do