Exit code is always 0 for non-interactive runner

[ffried]

The NonInteractiveShellRunner silently swallows error, leading to a 0 exit code even though the command failed:

https://github.com/spring-projects/spring-shell/blob/main/spring-shell-core/src/main/java/org/springframework/shell/core/NonInteractiveShellRunner.java#L158

We have jobs that rely on the exit code being non-zero on failures to e.g. be restarted or properly handled.
For that, we also have custom exit code mappers to make sure the exit code is set accordingly.

[fmbenhassine]

This is a valid issue. Thank you for raising it. However, the issue only happens when returning an ExitCode from the command. Throwing an exception from the command yields a non-zero exit as expected:

package org.springframework.shell.samples.noninteractive;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.shell.core.command.*;

@SpringBootApplication
public class SpringShellApplication {

	public static void main(String[] args) {
		System.setProperty("spring.shell.interactive.enabled", "false");
		SpringApplication.run(SpringShellApplication.class, "fail");
		// same output with the following:
		//System.exit(SpringApplication.exit(SpringApplication.run(SpringShellApplication.class, "fail")));
	}

	@Bean
	public Command fail() {
		return new AbstractCommand("fail", "A command that always fails") {

			@Override
			public ExitStatus doExecute(CommandContext commandContext) throws Exception {
				// throwing an exception will cause the app to exit with a non-zero exit code
				// throw new RuntimeException("Unable to execute command fail");

				// however, returning an exit status with a non-zero code will not cause the app to exit with that code
				return new ExitStatus(42, "Command execution failed");
			}
		};
	}

}

Moreover, I see that it is not possible to return a value from ShellRunner#run (this design seems to have been always like that by looking at previous versions, and I guess it was designed in a similar fashion to Boot's ApplicationRunner#run / CommandLineRunner#run). Customizing the exit code is exception-based by design, through ExitCodeExceptionMapper:

package org.springframework.shell.samples.noninteractive;

import org.springframework.boot.ExitCodeExceptionMapper;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.shell.core.command.*;

@SpringBootApplication
public class SpringShellApplication {

	public static void main(String[] args) {
		System.setProperty("spring.shell.interactive.enabled", "false");
		SpringApplication.run(SpringShellApplication.class, "fail");
		// same output with the following:
		//System.exit(SpringApplication.exit(SpringApplication.run(SpringShellApplication.class, "fail")));
	}

	@Bean
	public ExitCodeExceptionMapper exitCodeExceptionMapper() {
		return exception -> {
			if (exception instanceof CommandExecutionException e) {
				return e.getExitCode(); // this is missing as of v4.0.1, but should be possible
			}
			return 0;
		};
	}

	@Bean
	public Command fail() {
		return new AbstractCommand("fail", "A command that always fails") {

			@Override
			public ExitStatus doExecute(CommandContext commandContext) throws Exception {
				// with an exitCodeExceptionMapper, returning an exit status with a non-zero code should cause the app to exit with that code
				return new ExitStatus(42, "Command execution failed");
			}
		};
	}

}

Therefore, the shell should indeed throw an exception in this case to be able to intercept it in any custom exception mapper.