How do I opt out of deep-data merging in data files?

[AleksandrHovhannisyan]

Description

The 11ty docs on opting out of data merging mention that you can use an override: prefix to opt out of merging data for a specific front-matter variable:

Use the override: prefix on any data key to opt-out of this merge behavior for specific values or nested values.

{
  "tags": ["posts"]
}

---
override:tags: []
---

Even though normally the posts/firstpost.md file would inherit the posts tag from the directory data file (per normal data cascade rules), we can override the tags value to be an empty array to opt-out of this behavior.

But how would I opt out of deep data merging for data files? For example, suppose I have this file: src/_data/data.js:

// src/_data/data.js
module.exports = {
  key: "value",
}

And later, somewhere in a directory, I want to override this data file:

// src/_collection/collection.11tydata.js
module.exports = {
  "override:data": {
    key: "new-value"
  }
}

Unfortunately, this doesn't work. Is this not supported, or do I need to use a different syntax?

Steps to repro

1. Clone https://github.com/AleksandrHovhannisyan/11ty-sandbox/tree/merge-override
2. Run yarn to install dependencies.
3. Run yarn serve.
4. Observe that { "key1": "value1", "key2": "value2" } is logged in the server console.
5. Expectation: Only { "key2": "value2" } gets logged.

[zachleat]

and just to be clear you don’t want to use eleventyConfig.setDataDeepMerge(false);?

[AleksandrHovhannisyan]

Correct, just opt out in this one instance but deep merge everywhere else.

[AleksandrHovhannisyan]

And sorry, the example I provided wasn't the best. Here's a better one:

// src/_data/data.js
module.exports = {
  key1: "value1",
};

// src/_collection/_collection.11tydata.js
module.exports = {
  "override:data": {
    key2: "value2",
  },
};

Current behavior gives us this JSON for data:

{
  "key1": "value1",
  "key2": "value2"
}

Expected shape for data:

{
  "key2": "value2"
}

[AleksandrHovhannisyan]

Hey, just a quick follow up on this issue. I would be happy to put in a fix myself since I know you're busy. I've created a repro sandbox here that can be cloned: https://github.com/AleksandrHovhannisyan/11ty-sandbox/tree/merge-override. I've updated the original post here to mention repro steps.

I was looking through the code, and what I found confusing is that the tests seem to already account for this case:

eleventy/test/MergeTest.js

Line 47 in ecd0579

t.deepEqual(Merge({ a: [1] }, { "override:a": [2] }), { a: [2] });

The only usage of Merge that I could find is here:

eleventy/src/Plugins/RenderPlugin.js

Lines 380 to 384 in ecd0579

	async getData(...data) {
	let globalData = await this.initialGlobalData.getData();
	let merged = Merge({}, globalData, ...data);
	return merged;
	}

In my example above, Merge would get called with these arguments once data is spread:

Merge({}, { "key1": "value1", { "override:data": { key2: "value2" } });

So I wonder why that doesn't work...

Edit: Oh, maybe it's because the global data file (in this example, src/_data/data.js) is not keyed in by data anywhere... It's just { "key1": "value1" }. So there's no way to override it. I could override key1, but I couldn't override the entire object. I would have to export { data: { key1: "value1" } } from data.js if I wanted this to work. Which is a little annoying because then I'd have to do data.data.key1 in templates.