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

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

@@ -94,15 +94,16 @@ export abstract class ArchitectCommandModule
   }
 
   private getArchitectProject(): string | undefined {
-    const workspace = this.context.workspace;
-    if (!workspace) {
-      return undefined;
-    }
-
-    const [, projectName] = this.context.args.positional;
+    const { options, positional } = this.context.args;
+    const [, projectName] = positional;
 
     if (projectName) {
-      return workspace.projects.has(projectName) ? projectName : undefined;
+      return projectName;
+    }
+
+    // Yargs allows positional args to be used as flags.
+    if (typeof options['project'] === 'string') {
+      return options['project'];
     }
 
     const target = this.getArchitectTarget();
@@ -114,8 +115,8 @@ 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 +136,17 @@ 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 +1,40 @@
+import { join } from 'path';
+import { expectFileNotToExist, expectFileToExist } from '../../utils/fs';
+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/);
+
+    // Yargs allows positional args to be passed as flags. Verify that in this case the project can be determined.
+    await ng('build', '--project=third-app', '--configuration=development');
+
+    process.chdir(join(startCwd, 'projects/second-app'));
+    await ng('build', '--configuration=development');
+  } finally {
+    // Restore path
+    process.chdir(startCwd);
+  }
+}