fix(@angular/cli): provide actionable error when project cannot be determined

When the workspace has multiple projects and we the project to use cannot be determined from the current working directory, we now issue an actionable error message.

Closes angular#23291

Author: alan-agius4

packages/angular/cli/src/command-builder/architect-command-module.ts

@@ -94,15 +94,10 @@ export abstract class ArchitectCommandModule
   }
 
   private getArchitectProject(): string | undefined {
-    const workspace = this.context.workspace;
-    if (!workspace) {
-      return undefined;
-    }
-
     const [, projectName] = this.context.args.positional;
 
     if (projectName) {
-      return workspace.projects.has(projectName) ? projectName : undefined;
+      return projectName;
     }
 
     const target = this.getArchitectTarget();
@@ -114,8 +109,8 @@ export abstract class ArchitectCommandModule
   @memoize
   private getProjectNamesByTarget(target: string): string[] | undefined {
     const workspace = this.getWorkspaceOrThrow();
-
     const allProjectsForTargetName: string[] = [];
+
     for (const [name, project] of workspace.projects) {
       if (project.targets.has(target)) {
         allProjectsForTargetName.push(name);
@@ -135,8 +130,17 @@ export abstract class ArchitectCommandModule
       }
 
       const maybeProject = getProjectByCwd(workspace);
-      if (maybeProject && allProjectsForTargetName.includes(maybeProject)) {
-        return [maybeProject];
+      if (maybeProject) {
+        return allProjectsForTargetName.includes(maybeProject) ? [maybeProject] : undefined;
+      }
+
+      const { getYargsCompletions, help } = this.context.args.options;
+      if (!getYargsCompletions && !help) {
+        // Only issue the below error when not in help / completion mode.
+        throw new CommandModuleError(
+          'Cannot determine project for command. ' +
+            'Pass the project name as a command line argument or change the current working directory to a project directory.',
+        );
       }
     }
 

tests/legacy-cli/e2e/tests/commands/project-cannot-be-determined-by-cwd.ts

@@ -0,0 +1,36 @@
+import { join } from 'path';
+import { execAndWaitForOutputToMatch, ng } from '../../utils/process';
+import { updateJsonFile } from '../../utils/project';
+import { expectToFail } from '../../utils/utils';
+
+export default async function () {
+  const errorMessage =
+    'Cannot determine project for command. ' +
+    'Pass the project name as a command line argument or change the current working directory to a project directory';
+
+  // Delete root project
+  await updateJsonFile('angular.json', (workspaceJson) => {
+    delete workspaceJson.projects['test-project'];
+  });
+
+  await ng('generate', 'app', 'second-app', '--skip-install');
+  await ng('generate', 'app', 'third-app', '--skip-install');
+
+  const startCwd = process.cwd();
+
+  try {
+    const { message } = await expectToFail(() => ng('build'));
+    if (!message.includes(errorMessage)) {
+      throw new Error(`Expected build to fail with: '${errorMessage}'.`);
+    }
+
+    // Help should still work
+    execAndWaitForOutputToMatch('ng', ['build', '--help'], /--configuration/);
+
+    process.chdir(join(startCwd, 'projects/second-app'));
+    await ng('build', '--configuration=development');
+  } finally {
+    // Restore path
+    process.chdir(startCwd);
+  }
+}