rust: Add eprint help to write to stderr

Summary:
Adding `file=sys.stderr` is a mouthful. Even more if we try to align on
always using LF (and not CRLF).

Reviewed By: shayne-fletcher

Differential Revision: D50080143

fbshipit-source-id: 360b90d25febd7281b0a308adf16171eb59a1e65

prelude/rust/tools/buildscript_run.py

@@ -15,12 +15,16 @@
 import subprocess
 import sys
 from pathlib import Path
-from typing import Dict, IO, NamedTuple
+from typing import Any, Dict, IO, NamedTuple
 
 
 IS_WINDOWS: bool = os.name == "nt"
 
 
+def eprint(*args: Any, **kwargs: Any) -> None:
+    print(*args, end="\n", file=sys.stderr, flush=True, **kwargs)
+
+
 def cfg_env(rustc_cfg: Path) -> Dict[str, str]:
     with rustc_cfg.open(encoding="utf-8") as f:
         lines = f.readlines()
@@ -142,13 +146,13 @@ def ensure_rustc_available(
                 shell=IS_WINDOWS,
             )
     except OSError as ex:
-        print(f"Failed to run {rustc} because {ex}", file=sys.stderr)
+        eprint(f"Failed to run {rustc} because {ex}")
         sys.exit(1)
     except subprocess.CalledProcessError as ex:
-        print(f"Command failed with exit code {ex.returncode}", file=sys.stderr)
-        print(f"Command: {ex.cmd}", file=sys.stderr)
+        eprint(f"Command failed with exit code {ex.returncode}")
+        eprint(f"Command: {ex.cmd}")
         if ex.stdout:
-            print(f"Stdout: {ex.stdout}", file=sys.stderr)
+            eprint(f"Stdout: {ex.stdout}")
         sys.exit(1)
 
 
@@ -216,7 +220,7 @@ def main() -> None:  # noqa: C901
         if cargo_rustc_cfg_match:
             flags += "--cfg={}\n".format(cargo_rustc_cfg_match.group(1))
         else:
-            print(line)
+            print(line, end="\n")
     args.outfile.write(flags)
 
 

prelude/rust/tools/failure_filter_action.py

@@ -16,7 +16,11 @@
 import os
 import shutil
 import sys
-from typing import IO, List, NamedTuple, Optional, Tuple
+from typing import Any, IO, List, NamedTuple, Optional, Tuple
+
+
+def eprint(*args: Any, **kwargs: Any) -> None:
+    print(*args, end="\n", file=sys.stderr, flush=True, **kwargs)
 
 
 class Args(NamedTuple):
@@ -69,10 +73,7 @@ def main() -> int:
                     # Fall back to real copy if that doesn't work
                     shutil.copy(inp, out)
             else:
-                print(
-                    f"Missing required input file {short} ({inp})",
-                    file=sys.stderr,
-                )
+                eprint(f"Missing required input file {short} ({inp})")
                 return build_status["status"]
 
     # If all the required files were present, then success regardless of