[llvm] [llvm-lit] Add redirection handling for `env` command without args and write a lit test to check behavior with lit internal shell (PR #106629)

[via llvm-commits]

================
@@ -746,11 +746,25 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
                     env_str = "\n".join(
                         f"{key}={value}" for key, value in sorted(cmd_shenv.env.items())
                     )
-                    results.append(
-                        ShellCommandResult(
-                            j, env_str, "", 0, timeoutHelper.timeoutReached(), []
-                        )
+                    # Process redirections.
+                    stdin, stdout, stderr = processRedirects(
+                        j, default_stdin, cmd_shenv, opened_files
                     )
+                    if stdout != default_stdin:
----------------
Harini0924 wrote:

The input argument (`default_stdin`, which is set to `subprocess.PIPE`) is not always returned directly as `stdout` by the `processRedirects` function. The function's purpose is to handle any redirections specified in the command. If there's a redirection for `stdout` (like `>` or `>>`), `processRedirects` will open a file and return a file descriptor for that file instead of returning the original `subprocess.PIPE`.

So, when you pass `subprocess.PIPE` as the default for `stdout`, `processRedirects` might override it with a different file descriptor if redirection is specified. If no redirection is specified, then it could return `subprocess.PIPE` as it was originally passed. This means the condition `if stdout != default_stdin` is designed to check whether `stdout` was redirected to something other than the pipe, and it's not always true—it depends on whether any redirection was applied.

Did that answer your question?

https://github.com/llvm/llvm-project/pull/106629