core: "You're using escape sequences (${...}) with CDKTF Built-in functions" - false positive?

[elruwen]

Expected Behavior

No error message. I am not using escape sequences anywhere explicitly. I believe this is a false positive.

Actual Behavior

Given the following example application:

import {Construct} from "constructs";
import {App, Fn, TerraformStack, TerraformVariable} from "cdktf";
import {File} from "@cdktf/provider-local/lib/file";
import {LocalProvider} from "@cdktf/provider-local/lib/provider";

class MyStack extends TerraformStack {
    constructor(scope: Construct, id: string) {
        super(scope, id);

        new LocalProvider(this, "p")

        const myvar = new TerraformVariable(this, "prefix", {
            type: "string",
            default: "rwn-",
            description: "prefix",
        })

        const resources = [
            {
                foo: myvar.stringValue + "bar",
            },
            {
                bar: myvar.stringValue + "foo"
            }
        ]

        new File(this, "ruwen", {
            filename: `ruwen.yaml`,
            content: Fn.yamlencode(resources)
        })
    }
}

const app = new App();
new MyStack(app, "cdktf-playground");
app.synth();

This generates successfully the following yaml file without warnings:

- "foo": "rwn-bar"
- "bar": "rwn-foo"

But if I use the result from the Fn.yamlencode in another function, I am getting an error.

import {Construct} from "constructs";
import {App, Fn, TerraformStack, TerraformVariable} from "cdktf";
import {File} from "@cdktf/provider-local/lib/file";
import {LocalProvider} from "@cdktf/provider-local/lib/provider";

class MyStack extends TerraformStack {
    constructor(scope: Construct, id: string) {
        super(scope, id);

        new LocalProvider(this, "p")

        const myvar = new TerraformVariable(this, "prefix", {
            type: "string",
            default: "rwn-",
            description: "prefix",
        })

        const resources = [
            {
                foo: myvar.stringValue + "bar",
            },
            {
                bar: myvar.stringValue + "foo"
            }
        ]

        new File(this, "ruwen", {
            filename: `ruwen.yaml`,
            content: Fn.join("", [Fn.yamlencode(resources)])
        })
    }
}

const app = new App();
new MyStack(app, "cdktf-playground");
app.synth();

[2024-03-22T11:35:57.800] [ERROR] default - You're using escape sequences (${...}) with CDKTF Built-in functions. This is not supported yet, and the output may be incorrect.

[2024-03-22T11:35:57.800] [ERROR] default - yamlencode([{"foo" = "${${TfToken[TOKEN.0]}}bar"}, {"bar" = "${${TfToken[TOKEN.1]}}foo"}])
You're using escape sequences (${...}) with CDKTF Built-in functions. This is not supported yet, and the output may be incorrect.
yamlencode([{"foo" = "${${TfToken[TOKEN.0]}}bar"}, {"bar" = "${${TfToken[TOKEN.1]}}foo"}])

[2024-03-22T11:35:57.801] [ERROR] default - You're using escape sequences (${...}) with CDKTF Built-in functions. This is not supported yet, and the output may be incorrect.
yamlencode([{"foo" = "${${TfToken[TOKEN.0]}}bar"}, {"bar" = "${${TfToken[TOKEN.1]}}foo"}])

[2024-03-22T11:35:57.803] [ERROR] default - You're using escape sequences (${...}) with CDKTF Built-in functions. This is not supported yet, and the output may be incorrect.
yamlencode([{"foo" = "${${TfToken[TOKEN.0]}}bar"}, {"bar" = "${${TfToken[TOKEN.1]}}foo"}])

[2024-03-22T11:35:57.803] [ERROR] default - You're using escape sequences (${...}) with CDKTF Built-in functions. This is not supported yet, and the output may be incorrect.
yamlencode([{"foo" = "${${TfToken[TOKEN.0]}}bar"}, {"bar" = "${${TfToken[TOKEN.1]}}foo"}])

[2024-03-22T11:35:57.803] [ERROR] default - You're using escape sequences (${...}) with CDKTF Built-in functions. This is not supported yet, and the output may be incorrect.

The file still gets generated correctly.

If I do something wrong, then the error message should point to the spot where I use Fn.join. Because the yamlencode without the join works.
If it is a false positive, then the warning shouldn't be there.

Steps to Reproduce

See above

Versions

cdktf debug
language: typescript
cdktf-cli: 0.20.4
node: v18.15.0
cdktf: 0.20.5
constructs: 10.3.0
jsii: null
terraform: 1.7.5
arch: x64
os: linux 6.1.0-17-amd64
providers
@cdktf/provider-local (PREBUILT)
terraform provider version: 2.5.1
prebuilt provider version: 10.1.0
cdktf version: ^0.20.0

Providers

┌───────────────┬──────────────────┬─────────┬────────────┬───────────────────────┬─────────────────┐
│ Provider Name │ Provider Version │ CDKTF │ Constraint │ Package Name │ Package Version │
├───────────────┼──────────────────┼─────────┼────────────┼───────────────────────┼─────────────────┤
│ local │ 2.5.1 │ ^0.20.0 │ │ @cdktf/provider-local │ 10.1.0 │
└───────────────┴──────────────────┴─────────┴────────────┴───────────────────────┴─────────────────┘

Gist

No response

Possible Solutions

No response

Workarounds

No response

Anything Else?

No response

References

No response

Help Wanted

• I'm interested in contributing a fix myself

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[mutahhir]

I think the root of the problem might lie in this code:

                foo: myvar.stringValue + "bar",

If you were to replace this with Fn.join("", [myvar.stringValue, "bar"]), and try again, does the error go away?

[elruwen]

That works. But I think it is a bit tedious to use. Especially when it comes to format strings. And the generated code looks good. Do you have currently cases where it doesn't work?