avoid using file system in mpy_cross_compile()

Don't create a temporary directory for the input and output files.
Instead, we can use "-" as the file name to pipe directly to stdin
and stdout. This avoids issues with file system encoding and other odd
filesystem-related problems.

Author: dlech

src/mpy_cross_v6_3/__init__.py

@@ -1,7 +1,6 @@
 from enum import Enum
 import subprocess
 import sys
-import tempfile
 import pathlib
 import platform
 from typing import List, Optional, Tuple
@@ -75,44 +74,32 @@ def mpy_cross_compile(
         ...
 
     """
-    with tempfile.TemporaryDirectory() as tmp_dir_name:
-        tmp_dir = pathlib.Path(tmp_dir_name)
+    args: list[str] = [MPY_CROSS_PATH, "-", "-s", file_name]
 
-        with open(tmp_dir / "tmp.py", "w") as in_file:
-            in_file.write(file_contents)
+    if optimization_level is not None:
+        if optimization_level not in range(4):
+            raise ValueError("optimization_level must be between 0 and 3")
 
-        args: list[str] = [MPY_CROSS_PATH, in_file.name, "-s", file_name]
+        args.append(f"-O{optimization_level}")
 
-        if optimization_level is not None:
-            if optimization_level not in range(4):
-                raise ValueError("optimization_level must be between 0 and 3")
+    if small_number_bits is not None:
+        args.append(f"-msmall-int-bits={small_number_bits}")
 
-            args.append(f"-O{optimization_level}")
+    if arch is not None:
+        args.append(f"-march={arch.value}")
 
-        if small_number_bits is not None:
-            args.append(f"-msmall-int-bits={small_number_bits}")
+    if emit is not None:
+        args += ["-X", f"emit={emit.value}"]
 
-        if arch is not None:
-            args.append(f"-march={arch.value}")
+    if heap_size is not None:
+        args += ["-X", f"heapsize={heap_size}"]
 
-        if emit is not None:
-            args += ["-X", f"emit={emit.value}"]
+    if extra_args:
+        args += extra_args
 
-        if heap_size is not None:
-            args += ["-X", f"heapsize={heap_size}"]
+    process = subprocess.run(args, capture_output=True, input=file_contents.encode())
 
-        if extra_args:
-            args += extra_args
-
-        process = subprocess.run(args, capture_output=True)
-
-        try:
-            with open(tmp_dir / "tmp.mpy", "rb") as out_file:
-                data = out_file.read()
-        except OSError:
-            data = None
-
-        return process, data
+    return process, process.stdout if process.returncode == 0 else None
 
 
 def mpy_cross_version() -> str: