Bail with status code if file does not exist

composer.json

@@ -22,7 +22,11 @@
     },
     "config": {
         "process-timeout": 7200,
-        "sort-packages": true
+        "sort-packages": true,
+        "allow-plugins": {
+            "dealerdirect/phpcodesniffer-composer-installer": true,
+            "johnpbloch/wordpress-core-installer": true
+        }
     },
     "extra": {
         "branch-alias": {

features/import.feature

@@ -306,3 +306,38 @@ Feature: Import content.
       """
       (in file wordpress.000.xml)
       """
+
+    Scenario: Handling of non-existing files and directories
+      Given a WP install
+      And I run `wp plugin install --activate wordpress-importer`
+      And I run `wp export`
+      And save STDOUT 'Writing to file %s' as {EXPORT_FILE}
+      And an empty 'empty_test_directory' directory
+
+      When I try `wp import non_existing_relative_file_path.xml --authors=skip`
+      Then STDERR should contain:
+      """
+      Warning:
+      """
+      Then the return code should be 1
+
+      When I try `wp import non_existing_relative_file_path.xml {EXPORT_FILE} --authors=skip`
+      Then STDERR should contain:
+      """
+      Warning:
+      """
+      Then the return code should be 0
+
+      When I try `wp import empty_test_directory --authors=skip`
+      Then STDERR should contain:
+      """
+      Warning:
+      """
+      Then the return code should be 1
+
+      When I try `wp import empty_test_directory non_existing_relative_file_path.xml --authors=skip`
+      Then STDERR should contain:
+      """
+      Warning:
+      """
+      Then the return code should be 1

src/Import_Command.php

@@ -65,18 +65,32 @@ public function __invoke( $args, $assoc_args ) {
 				if ( ! empty( $files ) ) {
 					$new_args = array_merge( $new_args, $files );
 				}
+
+				if ( empty( $files ) ) {
+					WP_CLI::warning( "No files found in the import directory '$arg'." );
+				}
 			} else {
-				if ( file_exists( $arg ) ) {
+				if ( ! file_exists( $arg ) ) {
+					WP_CLI::warning( "File '$arg' doesn't exist." );
+					continue;
+				}
+
+				if ( is_readable( $arg ) ) {
 					$new_args[] = $arg;
+					continue;
 				}
+
+				WP_CLI::warning( "Cannot read file '$arg'." );
 			}
 		}
+
+		if ( empty( $new_args ) ) {
+			WP_CLI::error( 'Import failed due to missing or unreadable file/s.' );
+		}
+
 		$args = $new_args;
 
 		foreach ( $args as $file ) {
-			if ( ! is_readable( $file ) ) {
-				WP_CLI::warning( "Can't read '$file' file." );
-			}
 
 			$ret = $this->import_wxr( $file, $assoc_args );