Test Installed package detection in `pyproject.toml`

[karthiknadig]

Refs: #21141

• windows @meganrogge
• linux @gregvanl
• macOS @rebornix

Complexity: 2

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---

Requirements

1. Python 3.7 or greater
2. Latest python extension pre-release.

Verification steps:

1. Ensure you have python and python extension installed.
2. Make sure python extension is activated (open python file)
3. Create pyproject.toml with following content:

[project]
name = "spam"
version = "2020.0.0"
description = "Lovely Spam! Wonderful Spam!"
keywords = ["egg", "bacon", "sausage", "tomatoes", "Lobster Thermidor"]
dependencies = [
    "httpx",
    "gidgethub[httpx]",
    "django; os_name != 'nt'",
    "django; os_name == 'nt'",
]

[build-system]
# Minimum requirements for the build system to execute.
requires = ["setuptools", "wheel"] # PEP 508 specifications.

Things to check:

1. You should see hint squiggle like this, if the package is not installed. For os specific case you should see the squiggle only under the dependency that applies to your os. More environment markers here (https://peps.python.org/pep-0508/#environment-markers):
   

2. If you remove the [build-system] part and save, Create Environment button should go away.

3. If there are no dependencies or if all packages are installed then Create Environment button should go away.

Note: we don't trigger on file system events to detect package installs at this point. So you will need to close and reopen the file for this.
Note 2: We don't validate versions at this point. We only detect if a package is installed.