[llvm] [LIT] Fix env without subcommand causing early return in pipeline (PR #184028)

[Aaron Chen via llvm-commits]

================
@@ -831,16 +831,28 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
                     cmd_shenv = ShellEnvironment(shenv.cwd, shenv.env, shenv.umask)
                 args = updateEnv(cmd_shenv, args)
                 if not args:
-                    # Return the environment variables if no argument is provided.
-                    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(), []
+                    if len(cmd.commands) == 1:
+                        # Single command: return environment variables in-process.
+                        env_str = "\n".join(
+                            f"{key}={value}" for key, value in sorted(cmd_shenv.env.items())
                         )
-                    )
-                    return 0
+                        results.append(
+                            ShellCommandResult(
+                                j, env_str, "", 0, timeoutHelper.timeoutReached(), []
+                            )
+                        )
+                        return 0
+                    # Pipeline: replace with a subprocess that prints the
+                    # environment variables to stdout so the output can be
+                    # piped to the next command.
+                    args = [
+                        sys.executable,
+                        "-c",
+                        "import os, sys; sys.stdout.write("
+                        "'\\n'.join(k + '=' + v"
+                        " for k, v in sorted(os.environ.items())) + '\\n')",
+                    ]
----------------
nailo2c wrote:

How about moving the env printing logic into a standalone script in `builtin_commands` (like `env.py`)?

I think this would be easier to read and maintain than the current version, following the pattern we already use here:
https://github.com/llvm/llvm-project/blob/6d25af00ac475e0b1f7d2b7a9ca24a223930a8d2/llvm/utils/lit/lit/TestRunner.py#L982-L983

https://github.com/llvm/llvm-project/pull/184028