Deno Jupyter Kernel install not respecting new Jupyter v5 platform directories

[benjamincburns]

Version: Deno 2.1.9

Problem

Deno is currently installing its Jupyter kernel config to a deprecated installation location on macOS (and probably other platforms). It should be checking the JUPYTER_PLATFORM_DIRS environment variable, and installing to the updated location when it is set to a truthy value.

Background

In version 5 of jupyter_core, Jupyter has moved to a platform-specific directory structure and has deprecated the old one. If you use jupyter libraries that depend on jupyter_core (e.g. jupyter_client, in my case), it'll spit out a deprecation warning unless you set JUPYTER_PLATFORM_DIRS=1 in your environment.

When you set JUPYTER_PLATFORM_DIRS=1, it switches over to use the new directory structure. If kernel configs aren't installed in those locations, jupyter_core can't find them.

How to reproduce

In the example below (running on macOS), you can see that I've mirrored my existing kernel installs over to the new directory structure:

(bburns@ben) 2025-02-06T12:10:22+1300 😁 ~/projects
λ jupyter kernelspec list
Available kernels:
  sos        /Users/bburns/Library/Jupyter/kernels/sos
  python3    /Users/bburns/.pyenv/versions/3.11.11/share/jupyter/kernels/python3


(bburns@ben) 2025-02-06T12:10:30+1300 😁 ~/projects
λ JUPYTER_PLATFORM_DIRS=1 jupyter kernelspec list
Available kernels:
  sos        /Users/bburns/.local/share/jupyter/kernels/sos
  python3    /Users/bburns/.pyenv/versions/3.11.11/share/jupyter/kernels/python3

When I install deno's kernel with the JUPYTER_PLATFORM_DIRS env var set, jupyter can't find it.

(bburns@ben) 2025-02-06T12:10:37+1300 😁 ~/projects
λ JUPYTER_PLATFORM_DIRS=1 deno jupyter --install
Warning "deno jupyter" is unstable and might change in the future.
✅ Deno kernelspec installed successfully.


(bburns@ben) 2025-02-06T12:10:53+1300 😁 ~/projects
λ JUPYTER_PLATFORM_DIRS=1 jupyter kernelspec list
Available kernels:
  sos        /Users/bburns/.local/share/jupyter/kernels/sos
  python3    /Users/bburns/.pyenv/versions/3.11.11/share/jupyter/kernels/python3

However, if I drop back to the deprecated directory structure, it finds it in the old, deprecated location

(bburns@ben) 2025-02-06T12:10:58+1300 😁 ~/projects
λ jupyter kernelspec list
Available kernels:
  deno       /Users/bburns/Library/Jupyter/kernels/deno
  sos        /Users/bburns/Library/Jupyter/kernels/sos
  python3    /Users/bburns/.pyenv/versions/3.11.11/share/jupyter/kernels/python3

How to fix

When the JUPYTER_PLATFORM_DIRS env var is set on macOS, deno kernel install should install to $HOME/Library/Application Support/Jupyter/kernels rather than $HOME/Library/Jupyter/kernels.

I believe the install target for other platforms has changed as well, but I'm not sure what the most universal target should be for those.

[marvinhagemeister]

For anyone looking into this. The kernel installation code for Deno is here

deno/cli/tools/jupyter/install.rs

Lines 42 to 48 in 064cc0d

	pub fn install() -> Result<(), AnyError> {
	let user_data_dir = user_data_dir()?;
	let kernel_dir = user_data_dir.join("kernels").join("deno");
	std::fs::create_dir_all(&kernel_dir)?;
	let kernel_json_path = kernel_dir.join("kernel.json");

[benjamincburns]

If it's helpful at all, this is how I'm working around this issue in markdown-exec: https://github.com/pawamoy/markdown-exec/pull/70/files#diff-b803fcb7f17ed9235f1e5cb1fcd2f5d3b2838429d4368ae4c57ce4436577f03fR56-R104