+# Choose between lit's internal shell pipeline runner and a real shell. If
+# LIT_USE_INTERNAL_SHELL is in the environment, we use that as an override.
+use_lit_shell = os.environ.get("LIT_USE_INTERNAL_SHELL")
+if use_lit_shell:
+ # 0 is external, "" is default, and everything else is internal.
+ execute_external = (use_lit_shell == "0")
+else:
+ # Otherwise we default to internal on Windows and external elsewhere, as
+ # bash on Windows is usually very slow.
+ execute_external = (not sys.platform in ['win32'])
+