Making an environment extend itself causes pio to hang

[oatberry]

What kind of issue is this?

PlatformIO Core.

Configuration

Operating system: Windows 10

PlatformIO Version : 5.1.1

Description of problem

I accidentally made a build environment in my platformio.ini extend itself. This was a typo, but it caused commands like pio run --list-targets to silently hang until terminated by the user.

Steps to Reproduce

1. Create an environment definition in platformio.ini that extends itself
2. Attempt any pio command that requires parsing environments

Actual Results

pio does nothing and hangs

Expected Results

Perhaps there could be some kind of cycle detection to help users like myself catch typos in their configs.

[ivankravets]

Duplicate of #3883