Troubleshooting

Despite numerous forms of automatic code generation and validation, it's still possible to encounter misconfiguration where it's not clear what has gone wrong. While a validation error will tell you what is wrong, it doesn't do a lot to tell you where it is wrong. In these scenarios, a picture is worth a thousand words.

In order to make it easy to understand which services have been configured and for which types, ServiceCollection implements the std::fmt::Debug trait and, when the fmt feature is enabled, it also implements the std::fmt::Display trait with terminal colorization. You might take advantage of this capability for debug output, logging, or one-off inspection.

use di::*;

#[injectable]
struct Bar;

impl Bar {
    fn do_work(&self) {
       println!("Hello world!"); 
    }
}

trait Foo {
    fn do_work(&self);
}

#[injectable(Foo)]
struct FooImpl {
    bar: Ref<Bar>,
}

impl Foo for FooImpl {
    fn do_work(&self) {
        self.bar.do_work()
    }
}

fn main() {
    let mut services = ServiceCollection::new();

    services.add(Bar::transient())
            .add(FooImpl::transient());

    // we can print the service collection at any time, including here:
    // println!("{}\n", services);

    match services.build_provider() {
        Ok(provider) => {
            let foo = provider.get_required::<dyn Foo>();
            foo.do_work();
        },
        Err(validation_errors) => {
            // display the validation errors and entire service collection
            println!("{}\n{}", validation_errors, services);
        }
    }
}

A distinct difference between validation and display is that validation will only show errors, whereas display can show warnings and relationships.

Display Output

Symbols

  • ? = zero or one
  • * = zero or more
  • ⚿ = service key
  • ▲ = warning
  • ‼ = error
  • ♺ = circular reference
  • ⧗ = lifetime

Warnings

  • An optional service is missing
  • A list has no registered services

Errors

These are the same errors detected and raised by validation

  • A required service is missing
  • A service has a circular reference
  • A service with the lifetime ServiceLifetime::Singleton depends on a service with the lifetime ServiceLifetime::Scoped

Example Output

The following example demonstrates outputting an entire service hierarchy, including warnings and errors.

Colorization is supported when the fmt feature is activated

Display