options: fail when key is configured twice

src/restic/options/options.go

@@ -32,6 +32,11 @@ func Parse(in []string) (Options, error) {
 		if key == "" {
 			return Options{}, errors.Fatalf("empty key is not a valid option")
 		}
+
+		if v, ok := opts[key]; ok && v != value {
+			return Options{}, errors.Fatalf("key %q present more than once", key)
+		}
+
 		opts[key] = value
 	}
 

src/restic/options/options_test.go

@@ -33,6 +33,14 @@ var optsTests = []struct {
 			"k2": "more spaces = not evil",
 		},
 	},
+	{
+		[]string{"x=1", "foo=bar", "y=2", "foo=bar"},
+		Options{
+			"x":   "1",
+			"y":   "2",
+			"foo": "bar",
+		},
+	},
 }
 
 func TestParseOptions(t *testing.T) {
@@ -58,6 +66,10 @@ var invalidOptsTests = []struct {
 		[]string{"=bar", "bar=baz", "k="},
 		"empty key is not a valid option",
 	},
+	{
+		[]string{"x=1", "foo=bar", "y=2", "foo=baz"},
+		`key "foo" present more than once`,
+	},
 }
 
 func TestParseInvalidOptions(t *testing.T) {