fix(@angular-devkit/core): provide actionable warning when a workspace project has missing root property

The `root` property is required in a workspace project. Now we issue an actionable warning message when this is missing.

Note: this will become an error in the next major version.

Closes: #21310

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

@@ -60,8 +60,10 @@ export async function readJsonWorkspace(
       // TODO: Diagnostic reporting support
       throw new Error(message);
     },
-    warn(_message, _node) {
+    warn(message, _node) {
       // TODO: Diagnostic reporting support
+      // eslint-disable-next-line no-console
+      console.warn(message);
     },
   };
 
@@ -167,6 +169,13 @@ function parseProject(
   }
 
   const projectNodeValue = getNodeValue(projectNode);
+  if (!('root' in projectNodeValue)) {
+    // TODO(alan-agius4): change this to error in v15.
+    context.warn(
+      `Project "${projectName}" is missing a required property "root". This will become an error in the next major version.`,
+      projectNodeValue,
+    );
+  }
 
   for (const [name, value] of Object.entries<JsonValue>(projectNodeValue)) {
     switch (name) {

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

@@ -137,6 +137,24 @@ describe('readJsonWorkpace Parsing', () => {
       /version specifier not found/,
     );
   });
+
+  it('warns on missing root property in a project', async () => {
+    const host = createTestHost(stripIndent`
+      {
+        "version": 1,
+        "projects": {
+          "foo": {}
+        }
+      }
+    `);
+
+    const consoleWarnSpy = spyOn(console, 'warn').and.callFake(() => undefined);
+    await expectAsync(readJsonWorkspace('', host));
+
+    expect(consoleWarnSpy).toHaveBeenCalledWith(
+      `Project "foo" is missing a required property "root". This will become an error in the next major version.`,
+    );
+  });
 });
 
 describe('JSON WorkspaceDefinition Tracks Workspace Changes', () => {

packages/schematics/angular/utility/workspace_spec.ts

@@ -12,7 +12,9 @@ import { getWorkspace as readWorkspace, updateWorkspace, writeWorkspace } from '
 const TEST_WORKSPACE_CONTENT = JSON.stringify({
   version: 1,
   projects: {
-    'test': {},
+    test: {
+      root: '',
+    },
   },
 });