Handle empty/incomplete gcloud config file gracefully

lib/goth/config.ex

@@ -235,8 +235,19 @@ defmodule Goth.Config do
     if File.regular?(configuration_file) do
       configuration_data = configuration_file |> File.read!() |> decode_ini()
 
-      # Only retrieve the required data.
-      %{"project_id" => configuration_data["core"]["project"], "actor_email" => configuration_data["core"]["account"]}
+      case configuration_data do
+        %{"core" => %{"project" => project, "account" => account}} ->
+          %{"project_id" => project, "actor_email" => account}
+
+        _ ->
+          Logger.warning(
+            "Gcloud configuration file #{configuration_file} is missing " <>
+              "required [core] section with project and account settings. " <>
+              "Run 'gcloud init' or delete this file to resolve."
+          )
+
+          nil
+      end
     else
       nil
     end

test/data/home/gcloud/configurations/config_no_core

@@ -0,0 +1,3 @@
+[compute]
+zone = us-central1-c
+region = us-central1

test/goth/config_test.exs

@@ -150,6 +150,33 @@ defmodule Goth.ConfigTest do
     Application.start(:goth)
   end
 
+  test "get_configuration_data returns nil for empty config file" do
+    import ExUnit.CaptureLog
+
+    path = Path.expand("test/data/home/gcloud/configurations/config_empty")
+
+    log =
+      capture_log(fn ->
+        assert Config.get_configuration_data(path) == nil
+      end)
+
+    assert log =~ "missing required [core] section"
+    assert log =~ "Run 'gcloud init' or delete this file"
+  end
+
+  test "get_configuration_data returns nil for config file missing [core] section" do
+    import ExUnit.CaptureLog
+
+    path = Path.expand("test/data/home/gcloud/configurations/config_no_core")
+
+    log =
+      capture_log(fn ->
+        assert Config.get_configuration_data(path) == nil
+      end)
+
+    assert log =~ "missing required [core] section"
+  end
+
   test "GOOGLE_APPLICATION_CREDENTIALS is read" do
     # The test configuration sets an example JSON blob. We override it briefly
     # during this test.