Is it possible to define nested variables for evaluation?

[vlad-ivanov-name]

Hello, thank you for the awesome library!

I tried to look around but couldn't find this: is it possible to define nested identifiers and objects when evaluating with hcl::eval::Context?

For example, I'd like to evaluate the value of the following property:

  stages = stage.project_test.id

So I would need to make stage object available to context, then I would need to add project_test property, etc. Pretty much the same way it's done in terraform

[martinohmann]

Hi @vlad-ivanov-name,

your use case is already supported, just use a nested map and serialize it as a hcl::Value via hcl::to_value(map).

Here is a example (i'm using IndexMap here, but other maps like HashMap will also do):

use hcl::eval::Context;
use indexmap::indexmap;
use serde::Deserialize;

#[derive(Deserialize, Debug, PartialEq, Eq)]
struct Config {
    stages: u64,
}

let stages = indexmap! {
    "project_test" => indexmap! {
        "id" => 1,
    }
};

let mut ctx = Context::new();
ctx.declare_var("stage", hcl::to_value(stages).unwrap());

let input = "stages = stage.project_test.id";

let config: Config = hcl::eval::from_str(input, &ctx).unwrap();

assert_eq!(config, Config { stages: 1 });

It's also possible to do this with a map of structs or even just a struct as long as the struct implements Serialize:

use hcl::eval::Context;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;

#[derive(Deserialize, Debug, PartialEq, Eq)]
struct Config {
    stages: u64,
}

#[derive(Serialize)]
struct Stage {
    id: u64,
}

let mut stages = HashMap::new();
stages.insert("project_test", Stage { id: 1 });

let mut ctx = Context::new();
ctx.declare_var("stage", hcl::to_value(stages).unwrap());

let input = "stages = stage.project_test.id";

let config: Config = hcl::eval::from_str(input, &ctx).unwrap();

assert_eq!(config, Config { stages: 1 });

[martinohmann]

I'm planning to add some testable examples for use cases like this, but I'm currently short on time, so not sure when I will get to this.

[vlad-ivanov-name]

Thank you! I've also found that declaring variables as "body" also works:

        let mut ctx = hcl::eval::Context::new();

        let inner_body = hcl::Body::builder()
            .add_attribute(("id", 1))
            .build();

        let body = hcl::Body::builder()
            .add_attribute(("project_test", inner_body))
            .build();

        ctx.declare_var("stage", body);