Fix issue with merging observations config (hashicorp#31248)

Author: VioletHynes

command/server/config.go

@@ -447,8 +447,8 @@ func (c *Config) Merge(c2 *Config) *Config {
 		if c2.Observations.LedgerPath != "" {
 			result.Observations.LedgerPath = c2.Observations.LedgerPath
 		}
-		result.Observations.TypePrefixDenylist = append(c.Observations.TypePrefixDenylist, c2.Observations.TypePrefixDenylist...)
-		result.Observations.TypePrefixAllowlist = append(c.Observations.TypePrefixAllowlist, c2.Observations.TypePrefixAllowlist...)
+		result.Observations.TypePrefixDenylist = append(result.Observations.TypePrefixDenylist, c2.Observations.TypePrefixDenylist...)
+		result.Observations.TypePrefixAllowlist = append(result.Observations.TypePrefixAllowlist, c2.Observations.TypePrefixAllowlist...)
 		if c2.Observations.FileMode != "" {
 			result.Observations.FileMode = c2.Observations.FileMode
 		}

command/server/config_test.go

@@ -139,6 +139,27 @@ func Test_ObservationSystemConfigMerge(t *testing.T) {
 	require.Equal(t, "0777", merged.Observations.FileMode)
 }
 
+// Test_ObservationSystemConfigMergeFromNoObservations checks merge for observation system config from a config
+// without an observation system defined
+func Test_ObservationSystemConfigMergeFromNoObservations(t *testing.T) {
+	config, err := LoadConfigFile("./test-fixtures/config.hcl")
+	require.NoError(t, err)
+	require.NotNil(t, config)
+
+	config2, err := LoadConfigFile("./test-fixtures/observations_allow_deny.hcl")
+	require.NoError(t, err)
+	require.NotNil(t, config2)
+
+	merged := config.Merge(config2)
+	require.NotNil(t, merged)
+	require.NotNil(t, merged.Observations)
+	require.Equal(t, "/var/ledger.log", merged.Observations.LedgerPath)
+	require.Equal(t, []string{"deny1", "deny2"}, merged.Observations.TypePrefixDenylist)
+	require.Equal(t, []string{"allow1", "allow2", "allow3"}, merged.Observations.TypePrefixAllowlist)
+	require.Equal(t, "0777", merged.Observations.FileMode)
+	require.Equal(t, true, merged.EnableUI)
+}
+
 // TestDuplicateKeyValidationHcl checks that the server command displays a warning when the HCL config file contains duplicate keys.
 func TestDuplicateKeyValidationHcl(t *testing.T) {
 	testDuplicateKeyValidationHcl(t)