From 059dacdd3c45e08d64792b7704c261f775fb2e88 Mon Sep 17 00:00:00 2001
From: Tzu-ping Chung <uranusjr@gmail.com>
Date: Thu, 26 Jul 2018 17:04:59 +0800
Subject: [PATCH 1/2] Use COMSPEC for shell detection fallback

The subshell logic now considers:

* PIPENV_SHELL
* Auto detection
* SHELL (should very likely work for POSIX)
* PYENV_SHELL
* COMSPEC (should always work for Windows)
---
 pipenv/environments.py | 6 +++++-
 pipenv/shells.py       | 8 ++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/pipenv/environments.py b/pipenv/environments.py
index afe82988e1..6e0c865126 100644
--- a/pipenv/environments.py
+++ b/pipenv/environments.py
@@ -207,7 +207,11 @@
 PIPENV_SKIP_VALIDATION = True
 
 # Internal, the default shell to use if shell detection fails.
-PIPENV_SHELL = os.environ.get("SHELL") or os.environ.get("PYENV_SHELL")
+PIPENV_SHELL = (
+    os.environ.get("SHELL") or
+    os.environ.get("PYENV_SHELL") or
+    os.environ.get("COMSPEC")
+)
 
 # Internal, to tell if pyenv is installed.
 PYENV_ROOT = os.environ.get("PYENV_ROOT", os.path.expanduser("~/.pyenv"))
diff --git a/pipenv/shells.py b/pipenv/shells.py
index 10826f228a..70b236ea07 100644
--- a/pipenv/shells.py
+++ b/pipenv/shells.py
@@ -29,7 +29,7 @@ def detect_info():
     raise ShellDetectionFailure
 
 
-def _get_activate_script(venv):
+def _get_activate_script(cmd, venv):
     """Returns the string to activate a virtualenv.
 
     This is POSIX-only at the moment since the compat (pexpect-based) shell
@@ -37,11 +37,11 @@ def _get_activate_script(venv):
     """
     # Suffix and source command for other shells.
     # Support for fish shell.
-    if PIPENV_SHELL and "fish" in PIPENV_SHELL:
+    if "fish" in cmd:
         suffix = ".fish"
         command = "source"
     # Support for csh shell.
-    elif PIPENV_SHELL and "csh" in PIPENV_SHELL:
+    elif "csh" in cmd:
         suffix = ".csh"
         command = "source"
     else:
@@ -104,7 +104,7 @@ def fork_compat(self, venv, cwd, args):
         dims = get_terminal_size()
         with temp_environ():
             c = pexpect.spawn(self.cmd, ["-i"], dimensions=(dims.lines, dims.columns))
-        c.sendline(_get_activate_script(venv))
+        c.sendline(_get_activate_script(self.cmd, venv))
         if args:
             c.sendline(" ".join(args))
 

From 7758d745a8bed0c1da9fba31745378e58732029f Mon Sep 17 00:00:00 2001
From: Tzu-ping Chung <uranusjr@gmail.com>
Date: Mon, 30 Jul 2018 12:51:25 +0800
Subject: [PATCH 2/2] News

---
 news/2651.behavior | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 news/2651.behavior

diff --git a/news/2651.behavior b/news/2651.behavior
new file mode 100644
index 0000000000..be5f2d014d
--- /dev/null
+++ b/news/2651.behavior
@@ -0,0 +1,2 @@
+Add ``COMSPEC`` to fallback option (along with ``SHELL`` and ``PYENV_SHELL``)
+if shell detection fails, improving robustness on Windows.