fix: defensively handle nil maps and slices in marshaling (#18418)

Adds a custom marshaler to handle some cases where nils were being
marshaled to nulls, causing the web UI to throw an error.

---------

Co-authored-by: Steven Masley <stevenmasley@gmail.com>

coderd/idpsync/group.go

@@ -274,6 +274,17 @@ func (s *GroupSyncSettings) String() string {
 	return runtimeconfig.JSONString(s)
 }
 
+func (s *GroupSyncSettings) MarshalJSON() ([]byte, error) {
+	if s.Mapping == nil {
+		s.Mapping = make(map[string][]uuid.UUID)
+	}
+
+	// Aliasing the struct to avoid infinite recursion when calling json.Marshal
+	// on the struct itself.
+	type Alias GroupSyncSettings
+	return json.Marshal(&struct{ *Alias }{Alias: (*Alias)(s)})
+}
+
 type ExpectedGroup struct {
 	OrganizationID uuid.UUID
 	GroupID        *uuid.UUID

coderd/idpsync/idpsync_test.go

@@ -2,6 +2,7 @@ package idpsync_test
 
 import (
 	"encoding/json"
+	"regexp"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -9,6 +10,49 @@ import (
 	"github.com/coder/coder/v2/coderd/idpsync"
 )
 
+// TestMarshalJSONEmpty ensures no empty maps are marshaled as `null` in JSON.
+func TestMarshalJSONEmpty(t *testing.T) {
+	t.Parallel()
+
+	t.Run("Group", func(t *testing.T) {
+		t.Parallel()
+
+		output, err := json.Marshal(&idpsync.GroupSyncSettings{
+			RegexFilter: regexp.MustCompile(".*"),
+		})
+		require.NoError(t, err, "marshal empty group settings")
+		require.NotContains(t, string(output), "null")
+
+		require.JSONEq(t,
+			`{"field":"","mapping":{},"regex_filter":".*","auto_create_missing_groups":false}`,
+			string(output))
+	})
+
+	t.Run("Role", func(t *testing.T) {
+		t.Parallel()
+
+		output, err := json.Marshal(&idpsync.RoleSyncSettings{})
+		require.NoError(t, err, "marshal empty group settings")
+		require.NotContains(t, string(output), "null")
+
+		require.JSONEq(t,
+			`{"field":"","mapping":{}}`,
+			string(output))
+	})
+
+	t.Run("Organization", func(t *testing.T) {
+		t.Parallel()
+
+		output, err := json.Marshal(&idpsync.OrganizationSyncSettings{})
+		require.NoError(t, err, "marshal empty group settings")
+		require.NotContains(t, string(output), "null")
+
+		require.JSONEq(t,
+			`{"field":"","mapping":{},"assign_default":false}`,
+			string(output))
+	})
+}
+
 func TestParseStringSliceClaim(t *testing.T) {
 	t.Parallel()
 

coderd/idpsync/organization.go

@@ -234,6 +234,17 @@ func (s *OrganizationSyncSettings) String() string {
 	return runtimeconfig.JSONString(s)
 }
 
+func (s *OrganizationSyncSettings) MarshalJSON() ([]byte, error) {
+	if s.Mapping == nil {
+		s.Mapping = make(map[string][]uuid.UUID)
+	}
+
+	// Aliasing the struct to avoid infinite recursion when calling json.Marshal
+	// on the struct itself.
+	type Alias OrganizationSyncSettings
+	return json.Marshal(&struct{ *Alias }{Alias: (*Alias)(s)})
+}
+
 // ParseClaims will parse the claims and return the list of organizations the user
 // should sync to.
 func (s *OrganizationSyncSettings) ParseClaims(ctx context.Context, db database.Store, mergedClaims jwt.MapClaims) ([]uuid.UUID, error) {

coderd/idpsync/role.go

@@ -291,3 +291,14 @@ func (s *RoleSyncSettings) String() string {
 	}
 	return runtimeconfig.JSONString(s)
 }
+
+func (s *RoleSyncSettings) MarshalJSON() ([]byte, error) {
+	if s.Mapping == nil {
+		s.Mapping = make(map[string][]string)
+	}
+
+	// Aliasing the struct to avoid infinite recursion when calling json.Marshal
+	// on the struct itself.
+	type Alias RoleSyncSettings
+	return json.Marshal(&struct{ *Alias }{Alias: (*Alias)(s)})
+}

enterprise/coderd/idpsync.go

@@ -836,6 +836,9 @@ func (api *API) idpSyncClaimFieldValues(orgID uuid.UUID, rw http.ResponseWriter,
 		httpapi.InternalServerError(rw, err)
 		return
 	}
+	if fieldValues == nil {
+		fieldValues = []string{}
+	}
 
 	httpapi.Write(ctx, rw, http.StatusOK, fieldValues)
 }