Do not fingerprint error reason (#19)

Including the error reason among the fingerprinted parameters caused wrong error grouping in certain scenarios such as accessing not-existing map fields.

This pull request stores only the original reason in the error itself and then records each occurrence reason. This ensures that errors are grouped together even though the reason has slight changes.

I am not sure if it is worth to keep the reason in the error itself, but we can always remove it later so this doesn't have to be decided now.

Author: crbelaus

lib/error_tracker.ex

@@ -12,8 +12,20 @@ defmodule ErrorTracker do
   alias ErrorTracker.Repo
 
   def report(exception, stacktrace, given_context \\ %{}) do
+    {kind, reason} =
+      case exception do
+        %struct{} = ex when is_exception(ex) ->
+          {to_string(struct), Exception.message(ex)}
+
+        {_kind, %struct{} = ex} when is_exception(ex) ->
+          {to_string(struct), Exception.message(ex)}
+
+        {kind, ex} ->
+          {to_string(kind), to_string(ex)}
+      end
+
     {:ok, stacktrace} = ErrorTracker.Stacktrace.new(stacktrace)
-    {:ok, error} = Error.new(exception, stacktrace)
+    {:ok, error} = Error.new(kind, reason, stacktrace)
 
     context = Map.merge(get_context(), given_context)
 
@@ -24,7 +36,7 @@ defmodule ErrorTracker do
       )
 
     error
-    |> Ecto.build_assoc(:occurrences, stacktrace: stacktrace, context: context)
+    |> Ecto.build_assoc(:occurrences, stacktrace: stacktrace, context: context, reason: reason)
     |> Repo.insert!()
   end
 

lib/error_tracker/migrations/postgres/v01.ex

@@ -22,6 +22,7 @@ defmodule ErrorTracker.Migrations.Postgres.V01 do
 
     create table(:error_tracker_occurrences, prefix: prefix) do
       add :context, :map, null: false
+      add :reason, :text, null: false
       add :stacktrace, :map, null: false
       add :error_id, references(:error_tracker_errors, on_delete: :delete_all), null: false
 

lib/error_tracker/schemas/error.ex

@@ -22,24 +22,11 @@ defmodule ErrorTracker.Error do
     timestamps(type: :utc_datetime_usec)
   end
 
-  def new(exception, stacktrace = %ErrorTracker.Stacktrace{}) do
+  def new(kind, reason, stacktrace = %ErrorTracker.Stacktrace{}) do
     source = ErrorTracker.Stacktrace.source(stacktrace)
 
-    {kind, reason} =
-      case exception do
-        %struct{} = ex when is_exception(ex) ->
-          {to_string(struct), Exception.message(ex)}
-
-        {_kind, %struct{} = ex} when is_exception(ex) ->
-          {to_string(struct), Exception.message(ex)}
-
-        {kind, ex} ->
-          {to_string(kind), to_string(ex)}
-      end
-
     params = [
       kind: to_string(kind),
-      reason: reason,
       source_line: "#{source.file}:#{source.line}",
       source_function: "#{source.module}.#{source.function}/#{source.arity}"
     ]
@@ -48,6 +35,7 @@ defmodule ErrorTracker.Error do
 
     %__MODULE__{}
     |> Ecto.Changeset.change(params)
+    |> Ecto.Changeset.put_change(:reason, reason)
     |> Ecto.Changeset.put_change(:fingerprint, Base.encode16(fingerprint))
     |> Ecto.Changeset.put_change(:last_occurrence_at, DateTime.utc_now())
     |> Ecto.Changeset.apply_action(:new)

lib/error_tracker/schemas/occurrence.ex

@@ -10,6 +10,7 @@ defmodule ErrorTracker.Occurrence do
 
   schema "error_tracker_occurrences" do
     field :context, :map
+    field :reason, :string
 
     embeds_one :stacktrace, ErrorTracker.Stacktrace
     belongs_to :error, ErrorTracker.Error

lib/error_tracker/web/live/show.html.heex

@@ -16,7 +16,7 @@
 <div class="grid grid-cols-1 md:grid-cols-4 md:space-x-3 mt-6 gap-2">
   <div class="px-3 md:col-span-3 md:border-r-2 md:border-gray-500 space-y-8">
     <.section title="Full message">
-      <pre class="overflow-auto p-4 bg-gray-600"><%= @error.reason %></pre>
+      <pre class="overflow-auto p-4 bg-gray-600"><%= @occurrence.reason %></pre>
     </.section>
 
     <.section title="Source">