fix(@angular-devkit/core): allow property remove with workspace API

Removal changes were previously being improperly recorded with the wrong parent.  A property can now be directly removed by setting the value to undefined or by using the delete operator.

packages/angular_devkit/core/src/workspace/json/test/cases/ObjectRemove.json

@@ -0,0 +1,13 @@
+{
+  "version": 1,
+  // Comment
+  "schematics": {
+    "@angular/schematics:component": {
+      "prefix": "abc"
+    }
+  },
+  "x-foo": {
+    "is": ["good", "great", "awesome"]
+  },
+  "x-bar": 5,
+}

packages/angular_devkit/core/src/workspace/json/test/cases/ObjectRemoveMultiple.json

@@ -0,0 +1,8 @@
+{
+  "version": 1,
+  // Comment
+  "x-foo": {
+    "is": ["good", "great", "awesome"]
+  },
+  "x-bar": 5,
+}

packages/angular_devkit/core/src/workspace/json/utilities.ts

@@ -207,6 +207,12 @@ function create(
       return value;
     },
     set(target: {}, p: PropertyKey, value: unknown): boolean {
+      if (value === undefined) {
+        // setting to undefined is equivalent to a delete
+        // tslint:disable-next-line: no-non-null-assertion
+        return this.deleteProperty!(target, p);
+      }
+
       if (typeof p === 'symbol' || Reflect.has(target, p)) {
         return Reflect.set(target, p, value);
       } else if (excluded.has(p) || (included && !included.has(p))) {
@@ -251,13 +257,23 @@ function create(
         if (cacheEntry.node) {
           alteredNodes.add(cacheEntry.node);
         }
-        reporter(propertyPath, cacheEntry.parent, cacheEntry.node, oldValue, undefined);
+        if (cacheEntry.parent.kind === 'keyvalue') {
+          // Remove the entire key/value pair from this JSON object
+          reporter(propertyPath, ast, cacheEntry.node, oldValue, undefined);
+        } else {
+          reporter(propertyPath, cacheEntry.parent, cacheEntry.node, oldValue, undefined);
+        }
       } else {
         const { node, parent } = findNode(ast, p);
         if (node) {
           cache.set(propertyPath, { node, parent, value: undefined });
           alteredNodes.add(node);
-          reporter(propertyPath, parent, node, node && node.value, undefined);
+          if (parent.kind === 'keyvalue') {
+            // Remove the entire key/value pair from this JSON object
+            reporter(propertyPath, ast, node, node && node.value, undefined);
+          } else {
+            reporter(propertyPath, parent, node, node && node.value, undefined);
+          }
         }
       }
 

packages/angular_devkit/core/src/workspace/json/writer_spec.ts

@@ -592,4 +592,35 @@ describe('writeJsonWorkpaceFile', () => {
 
     await writeJsonWorkspace(workspace, host, 'ObjectReplace3');
   });
+
+  it('removes a property when property value is set to undefined', async () => {
+    const host = createTestCaseHost(basicFile);
+
+    const workspace = await readJsonWorkspace('', host);
+
+    workspace.extensions['x-baz'] = undefined;
+
+    await writeJsonWorkspace(workspace, host, 'ObjectRemove');
+  });
+
+  it('removes a property when using delete operator', async () => {
+    const host = createTestCaseHost(basicFile);
+
+    const workspace = await readJsonWorkspace('', host);
+
+    delete workspace.extensions['x-baz'];
+
+    await writeJsonWorkspace(workspace, host, 'ObjectRemove');
+  });
+
+  it('removes multiple properties when using delete operator', async () => {
+    const host = createTestCaseHost(basicFile);
+
+    const workspace = await readJsonWorkspace('', host);
+
+    delete workspace.extensions['x-baz'];
+    delete workspace.extensions.schematics;
+
+    await writeJsonWorkspace(workspace, host, 'ObjectRemoveMultiple');
+  });
 });