Always prepend to PATH instead of replacing it

[karrtikr]

For #20822 #11039

Replacing as-is has its problems, for eg. pyenv asks their users to manipulate PATH in their init script: https://github.com/pyenv/pyenv#set-up-your-shell-environment-for-pyenv, which we could end up replacing.

Particularly for pyenv, it mean users not being able to find pyenv:

Prepending solves it for cases where initial PATH value is suffix of the final value:

But, in other cases, this means that we end up with the whole PATH thrice. This is because it prepends it twice:

• Once in shell integration script
• Once when creating a process

So the final value could be:

PATH=<activated_full_path><activated_full_path><original_path>

where <activated_full_path> refers to value of PATH environment variable post activation. eg.

Future plans:

microsoft/vscode#145234 could solve our issue though, as that means we can simply use this API in combination with a hidden terminal instead of launching a process to get env vars.

[anthonykim1]

Just wondering: Would there be any benefits/harm to having original PATH in the front? I guess having the original PATH in the front might cause problem in activating the newly created environment?

[karrtikr]

I guess having the original PATH in the front might cause problem in activating the newly created environment?

Correct, actually the entire point of activation is that activated path appears before original path, so that activated path is picked up first when searching for stuff in PATH.

[karrtikr]

But, in other cases, this means that we end up with the whole PATH thrice.

microsoft/vscode#145234 could solve our issue though, as that means we can simply use this API in combination with a hidden terminal instead of launching a process to get env vars.