feat: add deep-merge util (#1503)

Co-authored-by: Daniel Dyla <dyladan@users.noreply.github.com>

packages/opentelemetry-core/src/index.ts

@@ -36,5 +36,6 @@ export * from './trace/sampler/ParentOrElseSampler';
 export * from './trace/sampler/ProbabilitySampler';
 export * from './trace/TraceState';
 export * from './trace/IdGenerator';
+export * from './utils/deep-merge';
 export * from './utils/url';
 export * from './utils/wrap';

packages/opentelemetry-core/src/utils/deep-merge.ts

@@ -0,0 +1,67 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ *
+ * 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
+ *
+ *      https://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.
+ */
+
+/**
+ * Deeply merges a source object onto a target object.
+ * If a given property is an array in both source and target, the
+ * source property replaces the target property entirely.
+ * @param target
+ * @param source
+ * @param maxDepth avoids an infinite CPU loop. Defaults to 10.
+ * @returns a deeply merged object
+ */
+export function deepMerge(
+  target: Record<string, any>,
+  source: Record<string, any>,
+  maxDepth = 10
+) {
+  const merged = target;
+  if (maxDepth === 0) {
+    throw new Error('Max depth exceeded.');
+  }
+  for (const [prop, value] of Object.entries(source)) {
+    if (bothPropsAreObjects(target, source, prop)) {
+      if (bothPropsAreArrays(target, source, prop)) {
+        merged[prop] = value;
+      } else {
+        merged[prop] = deepMerge(target[prop], value, maxDepth - 1);
+      }
+    } else {
+      merged[prop] = value;
+    }
+  }
+  return merged;
+}
+
+function bothPropsAreObjects(
+  target: Record<string, any>,
+  source: Record<string, any>,
+  prop: string
+) {
+  return propIsObject(target, prop) && propIsObject(source, prop);
+}
+
+function propIsObject(object: any, prop: string) {
+  return typeof object[prop] === 'object' && object[prop] !== null;
+}
+
+function bothPropsAreArrays(
+  target: Record<string, any>,
+  source: Record<string, any>,
+  prop: string
+) {
+  return Array.isArray(source[prop]) && Array.isArray(target[prop]);
+}

packages/opentelemetry-core/test/utils/deep-merge.test.ts

@@ -0,0 +1,80 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ *
+ * 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
+ *
+ *      https://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 * as assert from 'assert';
+import { deepMerge } from '../../src/utils/deep-merge';
+
+describe('deepMerge', () => {
+  it('should deep merge two objects', () => {
+    const target = { a: 1, b: 1, d: 1, e: [4, 5, 6], f: { g: 1, h: 2 } };
+    const source = { a: 1, b: 2, c: 2, e: [1], f: { h: 1, i: 1 } };
+    const expected = {
+      a: 1,
+      b: 2,
+      c: 2,
+      d: 1,
+      e: [1],
+      f: { g: 1, h: 1, i: 1 },
+    };
+    const merged = deepMerge(target, source);
+    assert.deepEqual(merged, expected);
+  });
+
+  it('should replace array-props', () => {
+    const target = { a: [4, 5, 6] };
+    const source = { a: [1] };
+    const expected = {
+      a: [1],
+    };
+    const merged = deepMerge(target, source);
+    assert.deepEqual(merged, expected);
+  });
+
+  it('should override a primitive target prop by a structural source prop', () => {
+    const merged = deepMerge({ a: 1, b: 'c' }, { a: { b: 1 }, b: [{ d: 1 }] });
+    assert.deepEqual(merged, { a: { b: 1 }, b: [{ d: 1 }] });
+  });
+
+  it('should nullify and undefine as per source props', () => {
+    const target = { a: 1, b: 1, d: 1, e: [4, 5, 6], f: { g: 1, h: 2 } };
+    const source = {
+      a: null,
+      b: undefined,
+      c: 2,
+      e: [1, null, undefined],
+      f: { h: null, i: undefined },
+    };
+    const expected = {
+      a: null,
+      b: undefined,
+      c: 2,
+      d: 1,
+      e: [1, null, undefined],
+      f: { g: 1, h: null, i: undefined },
+    };
+    const merged = deepMerge(target, source);
+    assert.deepEqual(merged, expected);
+  });
+
+  it('should respect the max depth', () => {
+    assert.throws(() => {
+      deepMerge(
+        { a: { a: { a: { a: { a: { a: 1 } } } } } },
+        { a: { a: { a: { a: { a: { a: 1 } } } } } },
+        5
+      );
+    });
+  });
+});