[polly] [polly][llvm-lit] Enabled lit internal shell for polly test suite (PR #105704)

[Connie Zhu via llvm-commits]

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@@ -16,8 +16,15 @@ config.name = 'Polly - isl unit tests'
 #
 # For now we require '&&' between commands, until they get globally killed and
 # the test runner updated.
-execute_external = platform.system() != 'Windows'
-config.test_format = lit.formats.ShTest(execute_external)
+#
+# We prefer the lit internal shell which provides a better user experience on failures
+# unless the user explicitly disables it with LIT_USE_INTERNAL_SHELL=0 env var.
+use_lit_shell = True
+lit_shell_env = os.environ.get("LIT_USE_INTERNAL_SHELL")
+if lit_shell_env:
+  use_lit_shell = not lit.util.pythonize_bool(lit_shell_env)
+
+config.test_format = lit.formats.ShTest(execute_external=not use_lit_shell)
----------------
connieyzhu wrote:

None of the polly tests seem to require "shell", but many of the other test suites do. Right now we aren't able to completely remove `REQUIRES: shell` from all test files, and I'm not sure if there is a way to configure this just for polly without affecting the other suites. 

Not sure if that answered your question, so please let me know if you need further elaboration.

https://github.com/llvm/llvm-project/pull/105704