Print all env vars in pipx environment

[TomiBelan]

• I have added an entry to docs/changelog.md

Summary of changes

• Add PIPX_DEFAULT_PYTHON and USE_EMOJI to pipx environment
• Print both original environment and pipx computed values
• Remove "Only PIPX_HOME and PIPX_BIN_DIR can be set by users in the above list." (not true)

Test plan

Tested by running

$ pipx environment
Environment variables (set by user):

PIPX_HOME=
PIPX_BIN_DIR=
PIPX_SHARED_LIBS=
PIPX_DEFAULT_PYTHON=
USE_EMOJI=

Derived values (computed by pipx):

PIPX_HOME=/home/user/.local/share/pipx
PIPX_BIN_DIR=/home/user/.local/bin
PIPX_SHARED_LIBS=/home/user/.local/share/pipx/shared
PIPX_LOCAL_VENVS=/home/user/.local/share/pipx/venvs
PIPX_LOG_DIR=/home/user/.local/state/pipx/log
PIPX_TRASH_DIR=/home/user/.local/share/pipx/trash
PIPX_VENV_CACHEDIR=/home/user/.cache/pipx
PIPX_DEFAULT_PYTHON=/usr/bin/python3
USE_EMOJI=true

$ PIPX_HOME=~/otherhome pipx environment
Environment variables (set by user):

PIPX_HOME=/home/user/otherhome
PIPX_BIN_DIR=
PIPX_SHARED_LIBS=
PIPX_DEFAULT_PYTHON=
USE_EMOJI=

Derived values (computed by pipx):

PIPX_HOME=/home/user/otherhome
PIPX_BIN_DIR=/home/user/.local/bin
PIPX_SHARED_LIBS=/home/user/otherhome/shared
PIPX_LOCAL_VENVS=/home/user/otherhome/venvs
PIPX_LOG_DIR=/home/user/otherhome/logs
PIPX_TRASH_DIR=/home/user/otherhome/.trash
PIPX_VENV_CACHEDIR=/home/user/otherhome/.cache
PIPX_DEFAULT_PYTHON=/usr/bin/python3
USE_EMOJI=true

$ USE_EMOJI=n pipx environment
Environment variables (set by user):

PIPX_HOME=
PIPX_BIN_DIR=
PIPX_SHARED_LIBS=
PIPX_DEFAULT_PYTHON=
USE_EMOJI=n

Derived values (computed by pipx):

PIPX_HOME=/home/user/.local/share/pipx
PIPX_BIN_DIR=/home/user/.local/bin
PIPX_SHARED_LIBS=/home/user/.local/share/pipx/shared
PIPX_LOCAL_VENVS=/home/user/.local/share/pipx/venvs
PIPX_LOG_DIR=/home/user/.local/state/pipx/log
PIPX_TRASH_DIR=/home/user/.local/share/pipx/trash
PIPX_VENV_CACHEDIR=/home/user/.cache/pipx
PIPX_DEFAULT_PYTHON=/usr/bin/python3
USE_EMOJI=false

$ PIPX_DEFAULT_PYTHON=python3.11 pipx environment
Environment variables (set by user):

PIPX_HOME=
PIPX_BIN_DIR=
PIPX_SHARED_LIBS=
PIPX_DEFAULT_PYTHON=python3.11
USE_EMOJI=

Derived values (computed by pipx):

PIPX_HOME=/home/user/.local/share/pipx
PIPX_BIN_DIR=/home/user/.local/bin
PIPX_SHARED_LIBS=/home/user/.local/share/pipx/shared
PIPX_LOCAL_VENVS=/home/user/.local/share/pipx/venvs
PIPX_LOG_DIR=/home/user/.local/state/pipx/log
PIPX_TRASH_DIR=/home/user/.local/share/pipx/trash
PIPX_VENV_CACHEDIR=/home/user/.cache/pipx
PIPX_DEFAULT_PYTHON=/usr/bin/python3.11
USE_EMOJI=true

$ PIPX_DEFAULT_PYTHON=foo pipx environment
Traceback (most recent call last):
  File "/home/user/.local/bin/pipx", line 5, in <module>
    from pipx.main import cli
  File "/home/user/.local/lib/python3.11/site-packages/pipx/main.py", line 23, in <module>
    from pipx import commands, constants
  File "/home/user/.local/lib/python3.11/site-packages/pipx/commands/__init__.py", line 2, in <module>
    from pipx.commands.environment import environment
  File "/home/user/.local/lib/python3.11/site-packages/pipx/commands/environment.py", line 15, in <module>
    from pipx.interpreter import DEFAULT_PYTHON
  File "/home/user/.local/lib/python3.11/site-packages/pipx/interpreter.py", line 87, in <module>
    DEFAULT_PYTHON = _get_absolute_python_interpreter(env_default_python)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/pipx/interpreter.py", line 78, in _get_absolute_python_interpreter
    raise PipxError(f"Default python interpreter '{env_python}' is invalid.")
pipx.util.PipxError: Default python interpreter 'foo' is invalid.

[dukecat0]

Thanks!

[TomiBelan]

Thanks for your review!