feat: Improve filter validation to show error on misconfiguration (#45)

* feat: Improve filter validation to show error on misconfiguration

* fix: Lint issue with comments

internal/provider/connection/schema.go

@@ -31,6 +31,9 @@ func (r *connectionResource) Schema(_ context.Context, _ resource.SchemaRequest,
 				Optional: true,
 			},
 		},
+		Validators: []validator.Object{
+			validators.ExactlyOneChild(),
+		},
 	}
 
 	resp.Schema = schema.Schema{
@@ -111,6 +114,9 @@ func (r *connectionResource) Schema(_ context.Context, _ resource.SchemaRequest,
 								"path":    filterRulePropertySchema,
 								"query":   filterRulePropertySchema,
 							},
+							Validators: []validator.Object{
+								validators.AtLeastOneChild(),
+							},
 						},
 						"retry_rule": schema.SingleNestedAttribute{
 							Optional: true,

internal/validators/AtLeastOneChild.go

@@ -0,0 +1,52 @@
+package validators
+
+import (
+	"context"
+
+	"github.com/hashicorp/terraform-plugin-framework-validators/helpers/validatordiag"
+	"github.com/hashicorp/terraform-plugin-framework/schema/validator"
+)
+
+var _ validator.Object = atLeastOneChild{}
+
+// atLeastOneChild validates if the provided object has at least one child attribute.
+type atLeastOneChild struct {
+}
+
+func (validator atLeastOneChild) ValidateObject(ctx context.Context, req validator.ObjectRequest, resp *validator.ObjectResponse) {
+	// Only validate the attribute configuration value if it is known.
+	if req.ConfigValue.IsNull() || req.ConfigValue.IsUnknown() {
+		return
+	}
+	defined := make(map[string]bool)
+	count := 0
+	for key, attr := range req.ConfigValue.Attributes() {
+		if attr.IsUnknown() || attr.IsNull() {
+			continue
+		}
+		defined[key] = true
+		count++
+	}
+	if count < 1 {
+		resp.Diagnostics.Append(validatordiag.InvalidAttributeTypeDiagnostic(
+			req.Path,
+			validator.MarkdownDescription(ctx),
+			req.ConfigValue.String(),
+		))
+	}
+}
+
+func (validator atLeastOneChild) Description(ctx context.Context) string {
+	return "value must have at least one child attribute defined"
+}
+
+func (validator atLeastOneChild) MarkdownDescription(ctx context.Context) string {
+	return validator.Description(ctx)
+}
+
+// AtLeastOneChild returns an AttributeValidator which ensures that any configured
+// attribute object has at least one child attribute.
+// Null (unconfigured) and unknown values are skipped.
+func AtLeastOneChild() validator.Object {
+	return atLeastOneChild{}
+}

internal/validators/ExactlyOneChild.go

@@ -9,7 +9,7 @@ import (
 
 var _ validator.Object = exactlyOneChild{}
 
-// exactlyOneChild validates if the provided value is of type string and can be parsed as JSON.
+// exactlyOneChild validates if the provided object has exactly one child attribute.
 type exactlyOneChild struct {
 }