Fix Elixir 1.20.0-rc.0 warnings

Mainly this involves using the pin operator (`^`) in binary pattern
matches where the size is matched out of a binary.
`Mint.WebSocket.Frame.decode_opcode/1` is also refactored to pattern
match the map directly, resolving this warning:

     warning: incompatible types given to Map.fetch/2:

         Map.fetch(
           %{
             <<0::integer-size(4), ""::binary>> => :continuation,
             <<1::integer-size(4), ""::binary>> => :text,
             <<2::integer-size(4), ""::binary>> => :binary,
             <<8::integer-size(4), ""::binary>> => :close,
             <<9::integer-size(4), ""::binary>> => :ping,
             <<10::integer-size(4), ""::binary>> => :pong
           },
           opcode
         )

     the map:

         dynamic(%{bitstring() => :binary or :close or :continuation or :ping or :pong or :text})

     does not have all required keys:

         dynamic()

     therefore this function will always return :error

     where "opcode" was given the type:

         # type: dynamic()
         # from: lib/mint/web_socket/frame.ex:289:22
         opcode

     typing violation found at:
     │
 290 │     with :error <- Map.fetch(@reverse_opcodes, opcode) do
     │                        ~
     │
     └─ lib/mint/web_socket/frame.ex:290:24: Mint.WebSocket.Frame.decode_opcode/1

Author: the-mikedavis

.github/workflows/main.yml

@@ -12,18 +12,18 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - erlang: "28.1"
-            elixir: "1.19"
+          - erlang: "28.3"
+            elixir: "1.20.0-rc.1"
             lint: true
             coverage: true
             report: true
             dialyzer: true
           # One version down.
           - erlang: "27.2"
-            elixir: "1.18"
+            elixir: "1.19"
           # Oldest version. We technically support OTP 23 but hard to test in CI
           - erlang: "24.3"
-            elixir: "1.14"
+            elixir: "1.15"
     env:
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       MIX_ENV: test

lib/mint/web_socket/frame.ex

@@ -265,7 +265,7 @@ defmodule Mint.WebSocket.Frame do
   defp decode_payload_and_mask(payload, masked?) do
     with {:ok, payload_length, rest} <- decode_payload_length(payload),
          {:ok, mask, rest} <- decode_mask(rest, masked?),
-         <<payload::binary-size(payload_length), more::bitstring>> <- rest do
+         <<payload::binary-size(^payload_length), more::bitstring>> <- rest do
       {:ok, payload, mask, more}
     else
       partial when is_binary(partial) -> :buffer
@@ -287,8 +287,9 @@ defmodule Mint.WebSocket.Frame do
   end
 
   defp decode_opcode(opcode) do
-    with :error <- Map.fetch(@reverse_opcodes, opcode) do
-      {:error, {:unsupported_opcode, opcode}}
+    case @reverse_opcodes do
+      %{^opcode => kind} -> {:ok, kind}
+      _ -> {:error, {:unsupported_opcode, opcode}}
     end
   end
 

lib/mint/web_socket/per_message_deflate.ex

@@ -147,7 +147,7 @@ defmodule Mint.WebSocket.PerMessageDeflate do
     data_size = byte_size(deflated) - 4
 
     case deflated do
-      <<deflated::binary-size(data_size), 0x00, 0x00, 0xFF, 0xFF>> -> deflated
+      <<deflated::binary-size(^data_size), 0x00, 0x00, 0xFF, 0xFF>> -> deflated
       deflated -> deflated
     end
   end

mix.exs

@@ -7,7 +7,7 @@ defmodule MintWebSocket.MixProject do
     [
       app: :mint_web_socket,
       version: "1.0.5",
-      elixir: "~> 1.6",
+      elixir: "~> 1.15",
       elixirc_paths: elixirc_paths(Mix.env()),
       erlc_paths: erlc_paths(Mix.env()),
       start_permanent: Mix.env() == :prod,