Make it possible to customize the behavior when a Qute value is missing

[ia3andy]

Description
Currently, when a Qute value is missing, it is replaced by NOT_FOUND in the rendered result.
It would be useful to be able to let the consumer choose what he want to do: warning log, fail, use NOT_FOUND, use something else.

Implementation ideas
Maybe we should be able to define some kind of String MissingValueProvider#get(String expression) in which we could either return a String, throw an exception, log, ... depending on the choice.

[quarkusbot]

/cc @mkouba

[mkouba]

It is possible to customize this behavior but it's not documented yet ;-). You can register a io.quarkus.qute.ResultMapper via io.quarkus.qute.EngineBuilder.addResultMapper() that handles io.quarkus.qute.Results.Result.NOT_FOUND, e.g. something like:

class MyMapper implements ResultMapper {
   public boolean appliesTo(Origin origin, Object result) {
      return Result.NOT_FOUND.equals(result);
   }
   public String map(Object result, Expression expression) {
      // if result not found write the original expression, i.e. {item.price} 
      return "{" + expression.toOriginalString() + "}";
   }
}

In quarkus we use a result mapper to escape characters for HTML.

[ia3andy]

@mkouba ah cool :) closing then!

[mkouba]

I think that we have an issue to document the SPI. But it's a low priority given the fact that it's still evolving...

[ia3andy]

@mkouba I tried this:

static class MissingValueMapper implements ResultMapper {
        public boolean appliesTo(TemplateNode.Origin origin, Object result) {
            return Results.Result.NOT_FOUND.equals(result);
        }

        public String map(Object result, Expression expression) {
            throw new IllegalStateException("Missing required template value: {" + expression.toOriginalString() + "}");
        }
    }

ended up with:

java.lang.IllegalStateException: java.util.concurrent.TimeoutException

	at io.quarkus.qute.TemplateImpl$TemplateInstanceImpl.render(TemplateImpl.java:60)
	at io.quarkus.qute.Template.render(Template.java:48)
	at io.quarkus.devtools.project.codegen.codestarts.CodestartQute.processQuteContent(CodestartQute.java:28)
	at io.quarkus.devtools.project.codegen.codestarts.Codestarts.processQuteFile(Codestarts.java:185)

[mkouba]

Hm, that's possible. Let me try this, write a test and fix a bug ;-)