Allow installable to return custom steps

[karthiknadig]

See discussion here #93 (comment)

[jjjermiah]

Some general thoughts regarding the current way this works:

vscode-python-environments/src/common/pickers/packages.ts

Lines 325 to 367 in 6bc409d

	export async function getPackagesToInstallFromPackageManager(
	packageManager: InternalPackageManager,
	environment: PythonEnvironment,
	cachedInstallables?: Installable[],
	): Promise<string[] | undefined> {
	let installable: Installable[] = cachedInstallables ?? [];
	if (installable.length === 0 && packageManager.supportsGetInstallable) {
	installable = await getInstallables(packageManager, environment);
	}
	const packageType = installable.length > 0 ? await getPackageType() : PackageManagement.commonPackages;
	if (packageType === PackageManagement.workspaceDependencies) {
	try {
	const result = await getWorkspacePackages(installable);
	return result;
	} catch (ex) {
	if (packageManager.supportsGetInstallable && ex === QuickInputButtons.Back) {
	return getPackagesToInstallFromPackageManager(packageManager, environment, installable);
	}
	if (ex === QuickInputButtons.Back) {
	throw ex;
	}
	return undefined;
	}
	}
	if (packageType === PackageManagement.commonPackages) {
	try {
	const result = await getCommonPackagesToInstall();
	return result;
	} catch (ex) {
	if (packageManager.supportsGetInstallable && ex === QuickInputButtons.Back) {
	return getPackagesToInstallFromPackageManager(packageManager, environment, installable);
	}
	if (ex === QuickInputButtons.Back) {
	throw ex;
	}
	return undefined;
	}
	}
	return undefined;
	}

If I try the 'hack' discussed:

  async getInstallable?(
    environment: PythonEnvironment
  ): Promise<Installable[]> {
    const twoOptions = ["pypi", "conda"];
    let installableItems: Installable[] = twoOptions.map((pkg) => {
      return {
        displayName: pkg,
        args: ["add", pkg === "pypi" ? "--pypi" : ""],
        description: `Install source: ${pkg}`,
      };
    });

    return installableItems;
  }

the first visual after choosing to install packages is:

It looks like theres an assumption that the installable is coming from the workspace

In pixi, though we can let users install local editable packages and their optional-dependencies most of the package installation will come from repositories

• being able to plug into getPackagesToInstallFromPackageManager in some way, might just let extensions take over to handle letting users choose which packages

unfortunately, the number of packages available on i.e conda-forge is ~30k, and I'm not sure if caching all that information and creating an Installable list will take some time and might not be effective

• open to solutions though
• the previous hacky implementation in the extension was to re-query the API on every keystroke to find similar packages which worked pretty well.

I also have a similar hacky solution for querying the pypi api with a new query on every keystroke which i can help with using for a new feature to the common_packages.txt route

[karthiknadig]

The installable API feels weak in this scenario. I am planning on a different API that gives more control to allow custom installation steps.