fix: validate capability configuration before cluster creation

pkg/cfn/builder/capability.go

@@ -1,6 +1,8 @@
 package builder
 
 import (
+	"fmt"
+
 	gfneks "github.com/weaveworks/eksctl/pkg/goformation/cloudformation/eks"
 	gfnt "github.com/weaveworks/eksctl/pkg/goformation/cloudformation/types"
 
@@ -100,6 +102,13 @@ func convertConfiguration(config *api.CapabilityConfiguration) (*gfneks.Capabili
 		}
 	}
 
+	if config.ArgoCD.AWSIDC == nil {
+		// A typo in the config file (e.g. `awsIDC` instead of `awsIdc`) leaves
+		// AWSIDC nil because YAML is decoded case-sensitively via the JSON
+		// serializer; dereferencing it would panic instead of failing cleanly.
+		// See https://github.com/eksctl-io/eksctl/issues/8701.
+		return nil, fmt.Errorf("awsIdc configuration is required for ARGOCD capability")
+	}
 	req.ArgoCd.AWSIDC = &gfneks.ArgoCDAWSIDC{
 		IDCInstanceARN: gfnt.NewString(config.ArgoCD.AWSIDC.IDCInstanceARN),
 	}

pkg/cfn/builder/capability_test.go

@@ -0,0 +1,42 @@
+package builder_test
+
+import (
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+
+	api "github.com/weaveworks/eksctl/pkg/apis/eksctl.io/v1alpha5"
+	"github.com/weaveworks/eksctl/pkg/cfn/builder"
+)
+
+var _ = Describe("Capability", func() {
+	Describe("CapabilityResourceSet", func() {
+		var capability api.Capability
+
+		BeforeEach(func() {
+			capability = api.Capability{
+				Name: "my-capability",
+				Type: "ARGOCD",
+				Configuration: &api.CapabilityConfiguration{
+					ArgoCD: &api.ArgoCDConfiguration{
+						Namespace: "argocd",
+					},
+				},
+			}
+		})
+
+		It("renders AWSIDC configuration when provided", func() {
+			capability.Configuration.ArgoCD.AWSIDC = &api.ArgoCDAWSIDC{
+				IDCInstanceARN: "arn:aws:sso:::instance/ssoins-123",
+				IDCRegion:      "us-west-2",
+			}
+			rs := builder.NewCapabilityResourceSet("my-cluster", capability)
+			Expect(rs.AddAllResources()).To(Succeed())
+		})
+
+		It("returns a clean error instead of panicking when AWSIDC is missing", func() {
+			rs := builder.NewCapabilityResourceSet("my-cluster", capability)
+			err := rs.AddAllResources()
+			Expect(err).To(MatchError(ContainSubstring("awsIdc configuration is required for ARGOCD capability")))
+		})
+	})
+})

pkg/ctl/cmdutils/configfile.go

@@ -313,6 +313,11 @@ func NewCreateClusterLoader(cmd *Cmd, ngFilter *filter.NodeGroupFilter, ng *api.
 				return err
 			}
 		}
+		for _, capability := range clusterConfig.Capabilities {
+			if err := capability.Validate(); err != nil {
+				return err
+			}
+		}
 		if clusterConfig.IsAutoModeEnabled() {
 			if len(clusterConfig.NodeGroups) > 0 || len(clusterConfig.ManagedNodeGroups) > 0 {
 				return errors.New("creation of managed or self-managed nodegroups is not supported during cluster creation " +
@@ -1186,7 +1191,7 @@ func emptyConfigField(v reflect.Value) bool {
 		return v.Uint() == 0
 	case reflect.String:
 		return v.String() == ""
-	case reflect.Ptr, reflect.Slice, reflect.Map, reflect.Interface, reflect.Chan:
+	case reflect.Pointer, reflect.Slice, reflect.Map, reflect.Interface, reflect.Chan:
 		return v.IsNil()
 	case reflect.Bool:
 		return !v.Bool()