Upgrade Click and make use of shell detection

This introduces an additional environment variable "PIPENV_SHELL". If
set, shell detection is skipped completely. The old "SHELL"
introspection is kept as a fallback if detection fails.

pipenv/cli.py

@@ -14,9 +14,9 @@ from click import (
     version_option,
     BadParameter,
 )
-from click_completion import init as init_completion
-from click_completion import get_code
 from click_didyoumean import DYMCommandCollection
+
+import click_completion
 import crayons
 import delegator
 
@@ -26,7 +26,7 @@ from . import environments
 from .utils import is_valid_url
 
 # Enable shell completion.
-init_completion()
+click_completion.init()
 CONTEXT_SETTINGS = dict(help_option_names=['-h', '--help'])
 
 
@@ -165,20 +165,17 @@ def cli(
     completion=False,
 ):
     if completion:  # Handle this ASAP to make shell startup fast.
-        if environments.PIPENV_SHELL:
+        from . import shells
+        try:
+            shell = shells.detect_info()[0]
+        except shells.ShellDetectionFailure:
             echo(
-                get_code(
-                    shell=environments.PIPENV_SHELL.split(os.sep)[-1],
-                    prog_name='pipenv'
-                )
-            )
-        else:
-            echo(
-                'Please ensure that the {0} environment variable '
-                'is set.'.format(crayons.normal('SHELL', bold=True)),
+                'Fail to detect shell. Please provide the {0} environment '
+                'variable.'.format(crayons.normal('PIPENV_SHELL', bold=True)),
                 err=True,
             )
             sys.exit(1)
+        print(click_completion.get_code(shell=shell, prog_name='pipenv'))
         sys.exit(0)
 
     from .core import (

pipenv/environments.py

@@ -74,7 +74,8 @@ PYENV_INSTALLED = (
     bool(os.environ.get('PYENV_SHELL')) or bool(os.environ.get('PYENV_ROOT'))
 )
 SESSION_IS_INTERACTIVE = bool(os.isatty(sys.stdout.fileno()))
+PIPENV_SHELL_EXPLICIT = os.environ.get('PIPENV_SHELL')
 PIPENV_SHELL = os.environ.get('SHELL') or os.environ.get('PYENV_SHELL')
 PIPENV_CACHE_DIR = os.environ.get('PIPENV_CACHE_DIR', user_cache_dir('pipenv'))
 # Tells pipenv to override PyPI index urls with a mirror.
-PIPENV_PYPI_MIRROR = os.environ.get('PIPENV_PYPI_MIRROR')
+PIPENV_PYPI_MIRROR = os.environ.get('PIPENV_PYPI_MIRROR')

pipenv/shells.py

@@ -0,0 +1,23 @@
+import os
+
+from .environments import PIPENV_SHELL_EXPLICIT, PIPENV_SHELL
+from .vendor import shellingham
+
+
+class ShellDetectionFailure(shellingham.ShellDetectionFailure):
+    pass
+
+
+def _build_info(value):
+    return (os.path.splitext(os.path.basename(value))[0], value)
+
+
+def detect_info():
+    if PIPENV_SHELL_EXPLICIT:
+        return _build_info(PIPENV_SHELL_EXPLICIT)
+    try:
+        return shellingham.detect_shell()
+    except (shellingham.ShellDetectionFailure, TypeError):
+        if PIPENV_SHELL:
+            return _build_info(PIPENV_SHELL)
+    raise ShellDetectionFailure