SpringBoot Add more MustacheAutoConfiguration compiler options

Currently, MustacheAutoConfiguration compiler only support two options, loader and collector. Would you please add more options for convenience, e.g. defaultValue/nullValue.

public Mustache.Compiler mustacheCompiler(TemplateLoader mustacheTemplateLoader) {
        return Mustache.compiler().withLoader(mustacheTemplateLoader)
                .withCollector(collector());
    }

Comment From: snicoll

e.g. defaultValue/nullValue.

Thanks for the suggestion. We can improve the auto-configuration but I'd rather do that with concrete use cases rather than based on a couple suggestions. Do you have some concrete use case or some customizations you've applied in your own project you'd like to share?

Comment From: fjcanyue

In my own project, if I use default compiler, an exception will be thrown when template variable value is null. (e.g. one variable is an empty object, {{object.field}} will throw an exception)

So I have to create a customized configuration to avoid that, but not use MustacheEnvironmentCollector.

@Configuration
public class MustacheAutoConfiguration
        extends org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration {

    public MustacheAutoConfiguration(MustacheProperties mustache, Environment environment,
            ApplicationContext applicationContext) {
        super(mustache, environment, applicationContext);
    }

    @Override
    public Compiler mustacheCompiler(TemplateLoader mustacheTemplateLoader) {
        return Mustache.compiler().defaultValue("").withLoader(mustacheTemplateLoader);
    }
}

Comment From: snicoll

@fjcanyue Thanks for the feedback. FYI, auto-configurations are not meant to be extended that way. There is a @ConditionalOnMissingBean on the Compiler so all that code is unnecessary, really. All you need is to create a Compiler @Bean and inject the auto-configured TemplateLoader:

@Configuration
public class MyUserConfig {

    @Bean
    public Compiler mustacheCompiler(TemplateLoader mustacheTemplateLoader) {
        return Mustache.compiler().defaultValue("").withLoader(mustacheTemplateLoader);
    }

}

I'd be tempted to add a CompilerCustomizer so that you can register that only instead (i.e. keep the default values and just add your own).

Let's see what the rest of the team thinks.

Comment From: wilkinsona

I think it's worth doing something here. Recreating the existing Compiler configuration is a little bit involved due to the MustacheEnvironmentCollector. Perhaps it should be a bean? I think there's a case for some configuration properties (standardsMode, defaultValue, etc), some additional optional beans (Escaper, Formatter), and perhaps a customizer too. I'm not yet sure which combination of the three would be best.