TemplateMark not rendering complex data types

[martinhalford]

Context

Consider the template "Late Delivery and Penalty".

The model contains the definition:

import org.accordproject.time@0.3.0.{Month, Day, TemporalUnit, Duration, PeriodUnit, Period} from https://models.accordproject.org/time@0.3.0.cto

@template
asset LateDeliveryAndPenaltyContract extends Contract {
  ...etc...
  o Duration penaltyDuration
  ...etc...
}

The data.json reads as follows:

{
    "$class": "org.accordproject.latedeliveryandpenalty@0.18.0.LateDeliveryAndPenaltyContract",
     ...etc...
    "penaltyDuration": {
        "$class": "org.accordproject.time@0.3.0.Duration",
        "amount": 2,
        "unit": "days"
    },
     ...etc...
}

The grammar is defined as:

## Late Delivery and Penalty.

.... for every {{penaltyDuration}}

Expected Behavior

As per olde Template Studio, the text used to renders as:

Late Delivery and Penalty.
----

... for every 2 days

Actual Behavior

The Template Playground renders the same model, grammar and data as:

## Late Delivery and Penalty.

... for every {"$class":"org.accordproject.time@0.3.0.Duration","amount":2,"unit":"days"} 

[jatinder14]

@mttrbrts I am here for gsoc24
I want to contribute to this project https://playground.accordproject.org/
would you be able to guide me
from where I should start
I will be highly thankful to you

[Sulochan-khadka]

@martinhalford If possible, kindly mention the steps to reproduce. As it seems a standard procedure while writing down an issue and it helps me a lot while solving the issues.

[Shubh-Raj]

Hi @mttrbrts @dselman,
This issue is still reproducible. Here's a minimal reproduction:

Steps to Reproduce

1. Go to https://playground.accordproject.org/
2. Click "Load Sample" → "New (Blank)"
3. Paste this in each editor:
   Concerto Model:
   namespace test@1.0.0
   import org.accordproject.time@0.3.0.{Duration} from https://models.accordproject.org/time@0.3.0.cto
   @template
   concept MyContract {
   o Duration penaltyDuration
   }
   TemplateMark:
   The penalty is {{penaltyDuration}}.
   JSON Data:
   {
   "$class": "test@1.0.0.MyContract",
   "penaltyDuration": {
   "$class": "org.accordproject.time@0.3.0.Duration",
   "amount": 2,
   "unit": "days"
   }
   }

Result

Expected: The penalty is 2 days.
Actual: The penalty is {"$class":"org.accordproject.time@0.3.0.Duration","amount":2,"unit":"days"}.

Root Cause

The issue is in @accordproject/template-engine — it lacks formatters for complex types like Duration and falls back to JSON.stringify().
Workaround: Use TypeScript syntax: {{% return penaltyDuration.amount + ' ' + penaltyDuration.unit %}}
Happy to contribute a fix if you can confirm the right approach!

Screenshot

[Shubh-Raj]

Hi @mttrbrts @dselman,

I've implemented fixes for this issue using two different approaches. Maintainers can choose whichever fits best:

---

Option 1: Template Engine Fix (Upstream)

PR: accordproject/template-engine#52

Method: Adds type-aware formatters in TemplateMarkInterpreter so complex types are rendered correctly at the source.

Pros:

• Fixes the issue for all consumers of template-engine
• Clean, single source of truth

Cons:

• Requires release of new template-engine version
• Playground needs to update dependency after merge

---

Option 2: Playground Fix (Workaround)

PR: #488

Method: Post-processes the generated HTML using JSON.parse() to detect and format known complex types (Duration, Period, MonetaryAmount).

Pros:

• Quick fix, no upstream dependency

Cons:

• Regex-based detection may miss edge cases (nested objects, different namespaces)
• Not a "proper" fix — workaround that duplicates logic
• New types need to be manually added

---

Recommendation

I recommend Option 1 (template-engine fix) as the long-term solution, with Option 2 as a temporary workaround until the template-engine release is available.

Let me know which approach you'd prefer, or if any changes are needed!

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 10 days.