Improve error messages around Mix TCP failures, closes #14912

Author: josevalim

lib/mix/lib/mix/pubsub/subscriber.ex

@@ -21,8 +21,15 @@ defmodule Mix.PubSub.Subscriber do
   @impl true
   def init({}) do
     build_path = Mix.Project.build_path()
-    Mix.Sync.PubSub.subscribe(build_path)
-    {:ok, %{acc: []}}
+
+    case Mix.Sync.PubSub.subscribe(build_path) do
+      :ok ->
+        {:ok, %{acc: []}}
+
+      {:error, message} ->
+        IO.warn(message, [])
+        :ignore
+    end
   end
 
   @impl true

lib/mix/lib/mix/sync/lock.ex

@@ -153,9 +153,7 @@ defmodule Mix.Sync.Lock do
         end
 
       {:error, reason} ->
-        Mix.raise(
-          "failed to open a TCP socket while acquiring a lock, reason: #{inspect(reason)}"
-        )
+        Mix.raise("failed to acquire filesystem lock using TCP, reason: #{inspect(reason)}")
     end
   end
 

lib/mix/lib/mix/sync/pubsub.ex

@@ -44,10 +44,7 @@ defmodule Mix.Sync.PubSub do
   """
   @spec subscribe(String.t()) :: :ok
   def subscribe(key) do
-    case GenServer.call(@name, {:subscribe, self(), key}, :infinity) do
-      :ok -> :ok
-      {:error, message} -> Mix.raise(message)
-    end
+    GenServer.call(@name, {:subscribe, self(), key}, :infinity)
   end
 
   @doc """
@@ -201,8 +198,7 @@ defmodule Mix.Sync.PubSub do
         {:ok, %{state | port: port}}
 
       {:error, reason} ->
-        {:error,
-         "failed to open a TCP socket in #{inspect(__MODULE__)}.subscribe/1, reason: #{inspect(reason)}"}
+        {:error, "failed to subscribe to Mix events using TCP, reason: #{inspect(reason)}"}
     end
   end