Add validation rules to disable nullable elements in a list, when used inside @node or @relationshipProperties.

.changeset/sixty-clocks-design.md

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+---
+"@neo4j/introspector": patch
+---
+
+Changed how "@neo4j/introspector" generates list fields that now are generated as a list of non-nullable elements, as a list of nullable elements is not supported by Neo4j.

.changeset/tame-melons-confess.md

@@ -0,0 +1,5 @@
+---
+"@neo4j/graphql": patch
+---
+
+Added a validation rule to avoid defining fields as lists of nullable elements, as Neo4j does not support this.

packages/graphql/src/schema/validation/custom-rules/valid-types/valid-list-in-node-type.ts

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) "Neo4j"
+ * Neo4j Sweden AB [http://neo4j.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Kind, type ASTVisitor, type ObjectTypeDefinitionNode, type TypeNode } from "graphql";
+
+import type { SDLValidationContext } from "graphql/validation/ValidationContext";
+import {
+    cypherDirective,
+    nodeDirective,
+    relationshipDirective,
+    relationshipPropertiesDirective,
+} from "../../../../graphql/directives";
+import { assertValid, createGraphQLError, DocumentValidationError } from "../utils/document-validation-error";
+import { getInnerTypeName, getPrettyName } from "../utils/utils";
+
+/**
+ * Validates that list types used in type annotated with the node directive are supported by Neo4j
+ **/
+export function ValidListInNodeType(context: SDLValidationContext): ASTVisitor {
+    return {
+        ObjectTypeDefinition(objectTypeDefinitionNode: ObjectTypeDefinitionNode, _key, _parent) {
+            const { directives } = objectTypeDefinitionNode;
+
+            const nodeUsage = directives?.find((directive) => directive.name.value === nodeDirective.name);
+            const relationshipPropertiesUsage = directives?.find(
+                (directive) => directive.name.value === relationshipPropertiesDirective.name
+            );
+            if (!directives) {
+                return; // Skip when no directives are present
+            }
+
+            if (!nodeUsage && !relationshipPropertiesUsage) {
+                return; // Skip if is the type is neither annotated with node nor relationshipProperties
+            }
+
+            objectTypeDefinitionNode.fields?.forEach((fieldDefinitionNode) => {
+                const { type, directives } = fieldDefinitionNode;
+                if (
+                    directives &&
+                    directives.some(
+                        (directive) =>
+                            directive.name.value === cypherDirective.name ||
+                            directive.name.value === relationshipDirective.name
+                    )
+                ) {
+                    return; // Skip cypher fields and relationship fields, relationship fields have their own validation
+                }
+                const { isValid, errorMsg, errorPath } = assertValid(() => {
+                    const typePath = getTypePath(type);
+                    if (typePath.includes(Kind.LIST_TYPE)) {
+                        const wrappedType = getInnerTypeName(type);
+                        const validTypePaths: string[][] = [
+                            [Kind.LIST_TYPE, Kind.NON_NULL_TYPE, wrappedType],
+                            [Kind.NON_NULL_TYPE, Kind.LIST_TYPE, Kind.NON_NULL_TYPE, wrappedType],
+                        ];
+                        if (!findTypePathInTypePaths(typePath, validTypePaths)) {
+                            const typeStr = getPrettyName(type);
+
+                            const directiveName = (nodeUsage ?? relationshipPropertiesUsage)?.name?.value;
+                            throw new DocumentValidationError(
+                                `List of nullable elements are not supported in "@${directiveName}" types. Found: ${typeStr}`,
+                                []
+                            );
+                        }
+                    }
+                });
+
+                if (!isValid) {
+                    context.reportError(
+                        createGraphQLError({
+                            nodes: [fieldDefinitionNode],
+                            path: [objectTypeDefinitionNode.name.value, fieldDefinitionNode.name.value, ...errorPath],
+                            errorMsg,
+                        })
+                    );
+                }
+            });
+        },
+    };
+}
+
+function getTypePath(typeNode: TypeNode, currentPath: string[] = []): string[] {
+    if (typeNode.kind === Kind.NON_NULL_TYPE || typeNode.kind === Kind.LIST_TYPE) {
+        return getTypePath(typeNode.type, [...currentPath, typeNode.kind]);
+    }
+    return [...currentPath, typeNode.name.value];
+}
+
+function findTypePathInTypePaths(typePathToFind: string[], typePaths: string[][]): boolean {
+    const typePathString = typePathToFind.join();
+    return typePaths.some((typePath) => typePathString === typePath.join());
+}