Support zstd compression via the Python 3.14 compression module

Map --compression values to the compression package submodules so zstd
is available alongside gzip, lzma and bz2. Default remains gzip.

eris/__main__.py

@@ -69,7 +69,7 @@ Options:
   -t THEME, --theme=THEME          The pygment theme used for syntax
                                    highlighting. Defaults to "native".
   -c TYPE, --compression=TYPE      The type of compression used in the cache:
-                                   gzip, lzma, bz2, or none. Defaults to gzip.
+                                   gzip, lzma, bz2, zstd, or none. Defaults to gzip.
   --window                         Use a native GPU window instead of the terminal.
   --config=FILE_NAME               Use a custom config file instead of tools.toml.
 """
@@ -1284,7 +1284,7 @@ def check_arguments():
             print("--theme must be one of:", " ".join(themes))
             sys.exit(1)
     if arguments["--compression"] is not None:
-        compressions = ["gzip", "lzma", "bz2", "none"]
+        compressions = ["gzip", "lzma", "bz2", "zstd", "none"]
         if arguments["--compression"] not in compressions:
             print("--compression must be one of:", " ".join(compressions))
             sys.exit(1)

eris/tools.py

@@ -513,9 +513,14 @@ def dump_pickle_safe(object_, path, protocol=pickle.HIGHEST_PROTOCOL, open=open)
         os.rename(tmp_path, path)
 
 
+_COMPRESSION_MODULES = {"gzip": "gzip", "lzma": "lzma", "bz2": "bz2",
+                        "zstd": "zstd"}
+
+
 @functools.cache
 def compression_open_func(compression):
-    return open if compression == "none" else importlib.import_module(compression).open
+    return open if compression == "none" else \
+        importlib.import_module("compression." + _COMPRESSION_MODULES[compression]).open
 
 
 class Result:

tests/tools_test.py

@@ -1,7 +1,9 @@
 
 import contextlib
 import os
+import pickle
 import shutil
+import tempfile
 import unittest
 import unittest.mock
 
@@ -158,5 +160,25 @@ class LruCacheWithEvictionTestCase(unittest.TestCase):
         self._assert_cache(a, 1, 2, 2)
 
 
+class CompressionTestCase(unittest.TestCase):
+
+    def setUp(self):
+        self.temp_dir = tempfile.mkdtemp()
+
+    def tearDown(self):
+        shutil.rmtree(self.temp_dir)
+
+    def test_open_funcs_round_trip(self):
+        value = {"text": list(range(1000))}
+        for compression in ["gzip", "lzma", "bz2", "zstd", "none"]:
+            with self.subTest(compression=compression):
+                open_func = tools.compression_open_func(compression)
+                path = os.path.join(self.temp_dir, f"cache.{compression}")
+                with open_func(path, "wb") as cache_file:
+                    pickle.dump(value, cache_file)
+                with open_func(path, "rb") as cache_file:
+                    self.assertEqual(pickle.load(cache_file), value)
+
+
 if __name__ == "__main__":
     golden.main()