Add PIPENV_PROJECT_DIR environment variable

[matteius]

Summary

Adds a new PIPENV_PROJECT_DIR environment variable that is automatically set when running pipenv run or pipenv shell. This variable contains the path to the project root directory (where the Pipfile is located).

Motivation

This addresses a long-standing feature request (#2241) from 2018. Users needed a way to consistently run scripts that require project root relative paths, regardless of their current working directory.

Use Cases

1. Running scripts from subdirectories:

   cd project/src
   pipenv run test  # Now works because script can use $PIPENV_PROJECT_DIR

2. Scripts in [scripts] section:

   [scripts]
   test = "pytest $PIPENV_PROJECT_DIR/tests"
   mypy = "mypy --config-file=$PIPENV_PROJECT_DIR/mypy.ini $PIPENV_PROJECT_DIR/src"

3. Django projects with src layout:

   [scripts]
   manage = "python $PIPENV_PROJECT_DIR/src/manage.py"

Changes

1. pipenv/routines/shell.py:

   • Set PIPENV_PROJECT_DIR in both do_shell() and do_run()

2. docs/configuration.md:

   • Added new "Runtime Environment Variables" section
   • Documents PIPENV_ACTIVE, PIPENV_PROJECT_DIR, and VIRTUAL_ENV
   • Provides usage examples

Testing

# From project root
$ pipenv run bash -c 'echo $PIPENV_PROJECT_DIR'
/home/user/myproject

# From subdirectory
$ cd src && pipenv run bash -c 'echo $PIPENV_PROJECT_DIR'
/home/user/myproject

Related Environment Variables

Variable	Description
PIPENV_ACTIVE	Set to 1 when inside a Pipenv environment
PIPENV_PROJECT_DIR	Path to project root (NEW)
PIPENV_PIPFILE	Full path to Pipfile (user-configurable)
VIRTUAL_ENV	Path to the virtualenv

Fixes #2241

---

Pull Request opened by Augment Code with guidance from the PR author