From 00fed1a31fc21c97710d2ccebf251d213a1e9172 Mon Sep 17 00:00:00 2001
From: Joel Speed <joel.speed@hotmail.co.uk>
Date: Wed, 29 Apr 2020 19:45:26 +0100
Subject: [PATCH] Return an error when unknown options are found in the config
 file

---
 pkg/apis/options/load.go      |  4 +++-
 pkg/apis/options/load_test.go | 12 ++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/pkg/apis/options/load.go b/pkg/apis/options/load.go
index 72294c28..aeb39b9a 100644
--- a/pkg/apis/options/load.go
+++ b/pkg/apis/options/load.go
@@ -38,7 +38,9 @@ func Load(configFileName string, flagSet *pflag.FlagSet, into interface{}) error
 		return fmt.Errorf("unable to register flags: %w", err)
 	}
 
-	err = v.Unmarshal(into, decodeFromCfgTag)
+	// UnmarhsalExact will return an error if the config includes options that are
+	// not mapped to felds of the into struct
+	err = v.UnmarshalExact(into, decodeFromCfgTag)
 	if err != nil {
 		return fmt.Errorf("error unmarshalling config: %w", err)
 	}
diff --git a/pkg/apis/options/load_test.go b/pkg/apis/options/load_test.go
index 0d316fcd..49268018 100644
--- a/pkg/apis/options/load_test.go
+++ b/pkg/apis/options/load_test.go
@@ -283,6 +283,18 @@ var _ = Describe("Load", func() {
 					unexported: "unexported",
 				},
 			}),
+			Entry("with an unknown option in the config file", &testOptionsTableInput{
+				configFile:  []byte(`unknown_option="foo"`),
+				flagSet:     func() *pflag.FlagSet { return testOptionsFlagSet },
+				expectedErr: fmt.Errorf("error unmarshalling config: 1 error(s) decoding:\n\n* '' has invalid keys: unknown_option"),
+				// Viper will unmarshal before returning the error, so this is the default output
+				expectedOutput: &TestOptions{
+					StringOption: "default",
+					Sub: TestOptionSubStruct{
+						StringSliceOption: []string{"a", "b"},
+					},
+				},
+			}),
 		)
 	})
 })