cdktf: forExpressionForMap does not render correctly

[sapslaj]

Expected Behavior

Based on the documentation, I would expect the follow code using TerraformIterator and forExpressionForMap to render a correct expression.

const it = TerraformIterator.fromMap({
  a: "b",
  foo: "bar",
});

// Generate a `for` expression using that iterator.
// note: using a very simple expression here for brevity.
const expr = it.forExpressionForMap("key", "val");

// Observe result
new TerraformOutput(stack, "test", {
  value: expr,
});

I would expect something akin to the following HCL:

output "test" {
  value = { for key, val in { a = "b", foo = "bar" } : key => val }
}

or in JSON

{
  "output": {
    "test": {
      "value": "${{ for key, val in { a = \"b\", foo = \"bar\" } : key => val }}"
    }
  }
}

Actual Behavior

The input map is not correctly rendered.

output "test" {
  value = "${{ for key, val in [object Object]: key => val }}"
}

{
  "output": {
    "test": {
      "value": "${{ for key, val in [object Object]: key => val }}"
    }
  }
}

Steps to Reproduce

repro.ts:

import {
  App,
  TerraformIterator,
  TerraformOutput,
  TerraformStack,
} from "cdktf";

const app = new App();
const stack = new TerraformStack(app, "sadge");

// Create an iterator based on a pre-calculated map.
const it = TerraformIterator.fromMap({
  a: "b",
  foo: "bar",
});

// Generate a `for` expression using that iterator.
// note: using a very simple expression here for brevity.
const expr = it.forExpressionForMap("key", "val");

// Observe result
new TerraformOutput(stack, "test", {
  value: expr,
});

app.synth();

npx ts-node repro.ts

Versions

cdktf debug
language: typescript
cdktf-cli: 0.20.3
node: v20.10.0
cdktf: 0.20.4
constructs: null
jsii: null
terraform: 1.6.2
arch: x64
os: linux 6.7.8-arch1-1

Providers

N/A; issue with core cdktf

Gist

No response

Possible Solutions

terraform-cdk/packages/cdktf/lib/tfExpression.ts

Line 395 in 639b61a

const input = this.resolveArg(context, this.input);

This is supposed to be returning a resolved token as a string. However, it is returning the input object as-is and that gets [object Object]'d a few lines down:

terraform-cdk/packages/cdktf/lib/tfExpression.ts

Line 402 in 639b61a

expr = `{ for ${key}, ${value} in ${input}: ${keyExpr} => ${valueExpr} }`;

Workarounds

This isn't the most ideal but building the expression by hand is a workaround.

const expr = '${{ for key, val in ' + JSON.stringify(map) + ' : key => val }}';

JSON.stringify probably isn't a great way to get that map in, but that was the easiest I could find. The logic that seems to be used for other expression builders is locked away in the un-exported TFExpression class 😞. renderMap is exported, however that implementation inserts newlines which is not desirable for this particular use case.

Anything Else?

No response

References

No response

Help Wanted

• I'm interested in contributing a fix myself

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[github-actions]

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