Task: Add mockable wrapper for :dbg (#318)

* Add :dbg service wrapper

* Refactor typespecs

Author: hhubert6

lib/live_debugger/gen_servers/callback_tracing_server.ex

@@ -7,6 +7,7 @@ defmodule LiveDebugger.GenServers.CallbackTracingServer do
 
   require Logger
 
+  alias LiveDebugger.Services.System.DbgService, as: Dbg
   alias LiveDebugger.Services.ModuleDiscoveryService
   alias LiveDebugger.Services.ChannelService
   alias LiveDebugger.Services.TraceService
@@ -63,8 +64,8 @@ defmodule LiveDebugger.GenServers.CallbackTracingServer do
 
   @impl true
   def handle_info(:setup_tracing, table_refs) do
-    :dbg.tracer(:process, {&handle_trace/2, 0})
-    :dbg.p(:all, :c)
+    Dbg.tracer(:process, {&handle_trace/2, 0})
+    Dbg.p(:all, :c)
 
     all_modules = ModuleDiscoveryService.all_modules()
 
@@ -77,11 +78,11 @@ defmodule LiveDebugger.GenServers.CallbackTracingServer do
     |> ModuleDiscoveryService.live_component_modules()
     |> CallbackUtils.live_component_callbacks()
     |> Enum.concat(callbacks)
-    |> Enum.each(fn mfa -> :dbg.tp(mfa, []) end)
+    |> Enum.each(fn mfa -> Dbg.tp(mfa, []) end)
 
     # This is not a callback created by user
     # We trace it to refresh the components tree
-    :dbg.tp({Phoenix.LiveView.Diff, :delete_component, 2}, [])
+    Dbg.tp({Phoenix.LiveView.Diff, :delete_component, 2}, [])
 
     {:noreply, table_refs}
   end

lib/live_debugger/services/system/dbg_service.ex

@@ -0,0 +1,82 @@
+defmodule LiveDebugger.Services.System.DbgService do
+  @moduledoc """
+  This module provides wrappers for system functions that are used for debugging.
+  """
+
+  @type port_generator() :: (-> port())
+  @type handler_spec() :: {handler_fun(), initial_data :: term()}
+  @type handler_fun() :: (event :: term(), data :: term() -> new_data :: term())
+  @type module_spec() ::
+          (-> {tracer_module :: atom(), tracer_state :: term()})
+          | {tracer_module :: atom(), tracer_state :: term()}
+
+  @callback tracer(:port, port_generator()) :: {:ok, pid()} | {:error, term()}
+  @callback tracer(:process, handler_spec()) :: {:ok, pid()} | {:error, term()}
+  @callback tracer(:module, module_spec()) :: {:ok, pid()} | {:error, term()}
+  @callback tracer(:file, filename :: :file.name_all()) :: {:ok, pid()} | {:error, term()}
+
+  @type match_desc() :: [match_num()]
+  @type match_num() :: {:matched, node(), integer()} | {:matched, node(), 0, rPCError :: term()}
+
+  @callback p(item :: term(), flags :: term()) :: {:ok, match_desc()} | {:error, term()}
+
+  @callback tp(module() | mfa(), match_spec :: term()) :: {:ok, match_desc()} | {:error, term()}
+
+  @doc """
+  Wrapper for `:dbg.tracer/2` that starts a tracer for the given type and handler specification.
+  """
+  @spec tracer(:port, port_generator()) :: {:ok, pid()} | {:error, term()}
+  @spec tracer(:process, handler_spec()) :: {:ok, pid()} | {:error, term()}
+  @spec tracer(:module, module_spec()) :: {:ok, pid()} | {:error, term()}
+  @spec tracer(:file, filename :: :file.name_all()) :: {:ok, pid()} | {:error, term()}
+  def tracer(type, handler_spec) do
+    impl().tracer(type, handler_spec)
+  end
+
+  @doc """
+  Wrapper for `:dbg.p/2`.
+  Traces `Item` in accordance to the value specified by `Flags`.
+  `p` stands for **p**rocess.
+  """
+  @spec p(item :: term(), flags :: term()) :: {:ok, match_desc()} | {:error, term()}
+  def p(item, flags) do
+    impl().p(item, flags)
+  end
+
+  @doc """
+  Wrapper for `:dbg.tp/2` that sets up a trace pattern.
+  Enables call trace for one or more exported functions specified by `ModuleOrMFA`.
+  """
+  @spec tp(module() | mfa(), match_spec :: term()) :: {:ok, match_desc()} | {:error, term()}
+  def tp(module, match_spec) do
+    impl().tp(module, match_spec)
+  end
+
+  defp impl() do
+    Application.get_env(
+      :live_debugger,
+      :dbg_service,
+      __MODULE__.Impl
+    )
+  end
+
+  defmodule Impl do
+    @moduledoc false
+    @behaviour LiveDebugger.Services.System.DbgService
+
+    @impl true
+    def tracer(type, handler_spec) do
+      :dbg.tracer(type, handler_spec)
+    end
+
+    @impl true
+    def p(item, flags) do
+      :dbg.p(item, flags)
+    end
+
+    @impl true
+    def tp(module, match_spec) do
+      :dbg.tp(module, match_spec)
+    end
+  end
+end