Include metadata.json in the published package

[olejorgenb]

Starting with dbc 2.0.0, metadata.json is no longer included in the published wheel. It was present in 1.7.1 and earlier.

The dash_bootstrap_components/_components/metadata.json file contains the JS-level component type metadata (prop types, descriptions, defaults, etc.) that is generated by dash-generate-components during the build. It's the same file that all other Dash component packages ship (dash.dcc, dash.html, dash_ag_grid, dash_daq, etc.).

Verified by inspecting the wheels directly:

1.7.1 — present

dash_bootstrap_components/_components/metadata.json ✓

2.0.4 — absent
(no metadata.json anywhere in the wheel)

Why is the file useful?

I do see that the file is not explicitly documented as a build artifact to include in the package, but it can be quite useful for downstream tooling that reads metadata.json for code generation, introspection, or IDE support. And all of the built-in dash packages do include it.

It is less severe since the type annotations are richer after Dash 3. I believe they contain most/all of the same information.

---

Root cause

The migration to hatchling as build backend. Hatchling respects .gitignore by default, and the dbc .gitignore excludes _components/. The pyproject.toml whitelists specific generated files via [tool.hatch.build.targets.wheel] artifacts, but only *.py and *.min.js — metadata.json was not included:

  [tool.hatch.build.targets.wheel]
  artifacts = [
      "dash_bootstrap_components/_components/dash_bootstrap_components.min.js",
      "dash_bootstrap_components/_components/*.py",
  ]

[AnnMarieW]

Here is some more background information about metadata.json file. plotly/dash#3034

The file is large and no longer used by dash. It's excluded to reduce the bundle size. There are plans to exclude it in dash as well.

[olejorgenb]

Thanks,

There are plans to exclude it in dash as well.

That's good to know 👍 Though I think it's good to have the information available for tooling, and it's kinda hard to believe the size alone is a good argument for removal.

But then we can instead shift focus to extract the information from the type annotations, if that's the stance of the dash team :)

Feel free to close.

[AnnMarieW]

@olejorgenb Can you say more about how you are using the file?
It is still being generated during build. It's just not included in the package.

[olejorgenb]

We have build some systems on top of dash, where we use this info to generate code based on the custom component packages we use. So it does not help that the file is generated during build. (or - it would be very cumbersome to build all the packages we use ourself :))

But with the new type annotations in Dash 3 (which is a very nice change!) I'm 95% sure we can use those as a basis instead.

[olejorgenb]

It will be a bit of a hassle to extract the per property description from the docstring, but should be doable:

Keyword arguments:

- children (a list of or a singular dash component, string or number; optional):
    The children of this Button.

- id (string; optional):
    The ID of the Button.

This is much more conveniently available in the metadata.json file