Enable strict checking of config during CLI.

Signed-off-by: Aramis Sennyey <sennyeya@amazon.com>

packages/config-loader/api-report.md

@@ -180,14 +180,17 @@ export function loadConfigSchema(
 ): Promise<ConfigSchema>;
 
 // @public
-export type LoadConfigSchemaOptions =
+export type LoadConfigSchemaOptions = (
   | {
       dependencies: string[];
       packagePaths?: string[];
     }
   | {
       serialized: JsonObject;
-    };
+    }
+) & {
+  noUndeclaredProperties?: boolean;
+};
 
 // @public
 export function mergeConfigSchemas(schemas: JSONSchema7[]): JSONSchema7;

packages/config-loader/src/schema/compile.ts

@@ -25,6 +25,7 @@ import {
   CONFIG_VISIBILITIES,
   ConfigVisibility,
 } from './types';
+import { SchemaObject } from 'json-schema-traverse';
 
 /**
  * This takes a collection of Backstage configuration schemas from various
@@ -35,6 +36,9 @@ import {
  */
 export function compileConfigSchemas(
   schemas: ConfigSchemaPackageEntry[],
+  options?: {
+    noUndeclaredProperties?: boolean;
+  },
 ): ValidationFunc {
   // The ajv instance below is stateful and doesn't really allow for additional
   // output during validation. We work around this by having this extra piece
@@ -102,6 +106,18 @@ export function compileConfigSchemas(
 
   const merged = mergeConfigSchemas(schemas.map(_ => _.value));
 
+  if (options?.noUndeclaredProperties) {
+    traverse(merged, (schema: SchemaObject) => {
+      /**
+       * The `additionalProperties` key can only be applied to `type: object` in the JSON
+       *  schema.
+       */
+      if (schema?.type === 'object') {
+        schema.additionalProperties ||= false;
+      }
+    });
+  }
+
   const validate = ajv.compile(merged);
 
   const visibilityBySchemaPath = new Map<string, ConfigVisibility>();

packages/config-loader/src/schema/load.ts

@@ -32,12 +32,16 @@ import {
  * @public
  */
 export type LoadConfigSchemaOptions =
-  | {
-      dependencies: string[];
-      packagePaths?: string[];
-    }
-  | {
-      serialized: JsonObject;
+  | (
+      | {
+          dependencies: string[];
+          packagePaths?: string[];
+        }
+      | {
+          serialized: JsonObject;
+        }
+    ) & {
+      noUndeclaredProperties?: boolean;
     };
 
 function errorsToError(errors: ValidationError[]): Error {
@@ -77,7 +81,9 @@ export async function loadConfigSchema(
     schemas = serialized.schemas as ConfigSchemaPackageEntry[];
   }
 
-  const validate = compileConfigSchemas(schemas);
+  const validate = compileConfigSchemas(schemas, {
+    noUndeclaredProperties: options.noUndeclaredProperties,
+  });
 
   return {
     process(