Filter context only when tracking errors (#100)

Just a few additions to #94:
- We don't need to filter context when not tracking errors
- Mention how to filter context in the Getting Started guide

Author: crbelaus

guides/Getting Started.md

@@ -107,11 +107,13 @@ In certain cases, you may want to include some additional information when track
 
 The `ErrorTracker.set_context/1` function stores the given context in the current process so any errors that occur in that process (for example, a Phoenix request or an Oban job) will include this given context along with the default integration context.
 
+There are some requirements on the type of data that can be included in the context, so we recommend taking a look at `ErrorTracker.set_context/1` documentation
+
 ```elixir
 ErrorTracker.set_context(%{user_id: conn.assigns.current_user.id})
 ```
 
-There are some requirements on the type of data that can be included in the context, so we recommend taking a look at `set_context/1` documentation
+You may also want to sanitize or filter out some information from the context before saving it. To do that you can take a look at the `ErrorTracker.Filter` behaviour.
 
 ## Manual error tracking
 

lib/error_tracker.ex

@@ -118,10 +118,11 @@ defmodule ErrorTracker do
     {kind, reason} = normalize_exception(exception, stacktrace)
     {:ok, stacktrace} = ErrorTracker.Stacktrace.new(stacktrace)
     {:ok, error} = Error.new(kind, reason, stacktrace)
-    context = get_context() |> Map.merge(given_context) |> filter_context_data()
+    context = Map.merge(get_context(), given_context)
 
     if enabled?() && !ignored?(error, context) do
-      {_error, occurrence} = upsert_error!(error, stacktrace, context, reason)
+      sanitized_context = sanitize_context(context)
+      {_error, occurrence} = upsert_error!(error, stacktrace, sanitized_context, reason)
       occurrence
     else
       :noop
@@ -209,14 +210,12 @@ defmodule ErrorTracker do
     ignorer && ignorer.ignore?(error, context)
   end
 
-  defp filter_context_data(context) do
+  defp sanitize_context(context) do
     filter_mod = Application.get_env(:error_tracker, :filter)
 
-    if filter_mod do
-      filter_mod.sanitize(context)
-    else
-      context
-    end
+    if filter_mod,
+      do: filter_mod.sanitize(context),
+      else: context
   end
 
   defp normalize_exception(%struct{} = ex, _stacktrace) when is_exception(ex) do