[llvm] [lit][bazel] Fall back to a default PATHEXT when the variable is unset (PR #217416)

[via llvm-commits]

https://github.com/UebelAndre created https://github.com/llvm/llvm-project/pull/217416

When running tests on Windows with Bazel, we can enter a scenario where `PATHEXT` is stripped from the environment before python starts, resulting in binaries not being found. This change adds a common fallback in the event `PATHEXT` is ever undefined or set to an empty value.

>From 2a6de37cab23101cb9ccbc62555d666c9d6c72d4 Mon Sep 17 00:00:00 2001
From: UebelAndre <github at uebelandre.com>
Date: Wed, 19 Aug 2026 11:00:14 -0700
Subject: [PATCH] [lit][bazel] Fall back to a default PATHEXT when the variable
 is unset

---
 llvm/utils/lit/lit/util.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/llvm/utils/lit/lit/util.py b/llvm/utils/lit/lit/util.py
index 8ab109fe15d45..6bd435e4e74dc 100644
--- a/llvm/utils/lit/lit/util.py
+++ b/llvm/utils/lit/lit/util.py
@@ -131,6 +131,8 @@ def which(command, paths=None):
     # On Cygwin, 'PATHEXT' may exist but it should not be used.
     if os.pathsep == ";":
         pathext = os.environ.get("PATHEXT", "").split(";")
+        if not any(pathext):
+            pathext = [".COM", ".EXE", ".BAT", ".CMD"]
     else:
         pathext = [""]