From e504c73555c770a898c8df3f7be88548ee948c87 Mon Sep 17 00:00:00 2001
From: Oleg S <97077423+RobotSail@users.noreply.github.com>
Date: Wed, 1 Mar 2023 14:02:17 -0500
Subject: [PATCH] test merging json objects

Signed-off-by: Oleg S <97077423+RobotSail@users.noreply.github.com>
---
 .changeset/spotty-cougars-wink.md      |  7 ++
 packages/backend-app-api/api-report.md |  1 +
 packages/types/api-report.md           |  3 +
 packages/types/src/json.test.ts        | 94 +++++++++++++++++++++++++-
 packages/types/src/json.ts             |  5 +-
 5 files changed, 107 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/spotty-cougars-wink.md

diff --git a/.changeset/spotty-cougars-wink.md b/.changeset/spotty-cougars-wink.md
new file mode 100644
index 0000000000..4e8b97a164
--- /dev/null
+++ b/.changeset/spotty-cougars-wink.md
@@ -0,0 +1,7 @@
+---
+'@backstage/backend-app-api': minor
+'@backstage/config-loader': minor
+'@backstage/types': minor
+---
+
+Introduces the ability to merge configs and JsonObjects
diff --git a/packages/backend-app-api/api-report.md b/packages/backend-app-api/api-report.md
index e99135b3ec..ed84730fc0 100644
--- a/packages/backend-app-api/api-report.md
+++ b/packages/backend-app-api/api-report.md
@@ -178,6 +178,7 @@ export const lifecycleServiceFactory: () => ServiceFactory<
 export function loadBackendConfig(options: {
   remote?: LoadConfigOptionsRemote;
   argv: string[];
+  config?: JsonObject;
 }): Promise<{
   config: Config;
 }>;
diff --git a/packages/types/api-report.md b/packages/types/api-report.md
index 4b43f5daa6..e0b34203cf 100644
--- a/packages/types/api-report.md
+++ b/packages/types/api-report.md
@@ -29,6 +29,9 @@ export type JsonPrimitive = number | string | boolean | null;
 // @public
 export type JsonValue = JsonObject | JsonArray | JsonPrimitive;
 
+// @public
+export const mergeJson: (a: JsonObject, b: JsonObject) => JsonObject;
+
 // @public
 export type Observable<T> = {
   [Symbol.observable](): Observable<T>;
diff --git a/packages/types/src/json.test.ts b/packages/types/src/json.test.ts
index 7da0ef8a3e..277992f00f 100644
--- a/packages/types/src/json.test.ts
+++ b/packages/types/src/json.test.ts
@@ -14,7 +14,13 @@
  * limitations under the License.
  */
 
-import { JsonPrimitive, JsonArray, JsonObject, JsonValue } from './json';
+import {
+  JsonPrimitive,
+  JsonArray,
+  JsonObject,
+  JsonValue,
+  mergeJson,
+} from './json';
 
 describe('json', () => {
   it('JsonPrimitive', () => {
@@ -79,3 +85,89 @@ describe('json', () => {
     expect(true).toBe(true);
   });
 });
+
+describe('jsonMerge', () => {
+  it('should merge two objects', () => {
+    const obj1 = { a: 1, b: 2, c: 3 };
+    const obj2 = { b: 4, c: 5, d: 6 };
+    const merged = mergeJson(obj1, obj2);
+    expect(merged).toEqual({ a: 1, b: 4, c: 5, d: 6 });
+  });
+
+  it('should always prefer to merge the values of the second parameter', () => {
+    const obj1 = {
+      a: 1,
+      b: [1, 2, 3],
+      c: {
+        z: 1,
+        y: 2,
+        x: 3,
+      },
+    };
+    const obj2 = {
+      a: 2,
+      b: [2, 4, 6],
+      c: {
+        z: 2,
+        y: 4,
+        x: 6,
+      },
+    };
+    const merged = mergeJson(obj1, obj2);
+    expect(merged).toEqual(obj2);
+  });
+
+  it('should prefer the second argument whenever keys collide', () => {
+    const obj1 = {
+      a: 1,
+      b: [1, 2, 3],
+      c: {
+        z: 1,
+        y: 2,
+        x: 3,
+      },
+    };
+    const obj2 = {
+      a: 2,
+      c: {
+        y: 4,
+      },
+    };
+    const merged = mergeJson(obj1, obj2);
+    expect(merged).toEqual({
+      a: 2,
+      b: [1, 2, 3],
+      c: {
+        z: 1,
+        y: 4,
+        x: 3,
+      },
+    });
+  });
+
+  it('should merge recursively', () => {
+    const obj1 = {
+      backend: {
+        database: {
+          provider: 'sqlite3',
+        },
+      },
+    };
+    const obj2 = {
+      backend: {
+        database: {
+          password: 'password123',
+        },
+      },
+    };
+    const merged = mergeJson(obj1, obj2);
+    expect(merged).toEqual({
+      backend: {
+        database: {
+          provider: 'sqlite3',
+          password: 'password123',
+        },
+      },
+    });
+  });
+});
diff --git a/packages/types/src/json.ts b/packages/types/src/json.ts
index 1bfe0c543f..4b0bb958ef 100644
--- a/packages/types/src/json.ts
+++ b/packages/types/src/json.ts
@@ -47,9 +47,10 @@ export type JsonValue = JsonObject | JsonArray | JsonPrimitive;
  * prefers values from b, unless the value is an object, in which case it recursively
  * merges the values.
  *
- * @param a The base object
- * @param b The object to merge into a
+ * @param a - The base object
+ * @param b - The object to merge into a
  * @returns The merged object
+ * @public
  */
 export const mergeJson = (a: JsonObject, b: JsonObject): JsonObject => {
   const final: JsonObject = {};