fix: let upgrade --dry-run instantiate prefix for pypi

[lucascolley]

description: #2770 (comment)

Closes #2770

[Hofer-Julian]

Thanks for your contribution @lucascolley.

Since you marked this as draft: what is still missing? :)

[lucascolley]

I think I ready somewhere in the code that dry-run was about "writing to disk" or not - I guess we are breaking that model here, so maybe can adjust wherever I read that?

We can also remove the commented out line in the test.

The description of --dry-run in the docs says

Only show the changes that would be made, without actually updating the manifest, lock file, or environment.

Does this count as updating the environment? Either way, we should probably make it clear that users should also pass --no-install if they don't want this behaviour to happen.

[Hofer-Julian]

Only show the changes that would be made, without actually updating the manifest, lock file, or environment.

Ah yes, that expectation still holds true. I think we need to find a different way to fix #2770

[lucascolley]

A new --dry-run-pypi flag?

[Hofer-Julian]

A new --dry-run-pypi flag?

What would that flag do? :)

[lucascolley]

Well the "dry" part that I care about here is not performing the upgrade.

Behaviour	Main	This PR	What would that flag do? :)
Completely dry	--dry-run	--dry-run --no-install	--dry-run
Allow instantiation of prefix for PyPI, do not perform upgrade	impossible	--dry-run	--dry-run-pypi

[Hofer-Julian]

Understood. We'd probably have to think of a different name for this.

Let's wait for @ruben-arts to chime in on that one.

[ruben-arts]

What if we make the no install logic, still install a solve prefix for the pypi work? This might be a little confusing at first but atleast it's going to do what you need to perform the least amount of work for the command you ask from pixi.

[lucascolley]

That would work for me as long as it's documented clearly!

[lucascolley]

What if we make the no install logic, still install a solve prefix for the pypi work? This might be a little confusing at first but atleast it's going to do what you need to perform the least amount of work for the command you ask from pixi.

actually, what do you think @baszalmstra ? That seems to conflict with

pixi/src/lock_file/update.rs

Lines 804 to 809 in 352dc9e

	/// Defines if during the update-process it is allowed to create prefixes.
	/// This might be required to solve pypi dependencies because those require
	/// a python interpreter.
	pub(crate) fn with_no_install(self, no_install: bool) -> Self {
	Self { no_install, ..self }
	}