Atomically save prefs.yaml to prevent file corruption

This adds a dependency on the atomicwrites package. Note that it was
already a transitive dev-dependency, but is now a direct dependency as
well.

On Linux, atomicwrites fsyncs the directory after saving. This is
unnecessary for consistency after a system crash, and slows down program
shutdown slightly. But I'm too lazy to vendor or rewrite the library to
not fsync the directory.

corrscope/config.py

@@ -19,6 +19,7 @@ from typing import (
     Any,
     TextIO,
     Union,
+    IO,
 )
 
 import attr
@@ -64,10 +65,6 @@ class MyYAML(YAML):
             with stream.open("w", encoding="utf-8") as f:
                 self.dump_without_corrupting(data, f, **kwargs)
 
-        elif isinstance(stream, TextIO):
-            # Nobody actually calls dump(..., open()). This branch is never taken.
-            self.dump_without_corrupting(data, stream, **kwargs)
-
         elif stream is None:
             # Possibly only called in unit tests, not in production.
             stream = StringIO()
@@ -75,9 +72,8 @@ class MyYAML(YAML):
             return stream.getvalue()
 
         else:
-            raise TypeError(
+            # with atomic_write(...) as f: dump(..., f)
-                f"stream must be {{Path, TextIO=open(), None}}, but is {type(stream)}"
+            self.dump_without_corrupting(data, stream, **kwargs)
-            )
 
     def dump_without_corrupting(self, *args, **kwargs):
         YAML.dump(self, *args, **kwargs)

corrscope/settings/global_prefs.py

@@ -1,5 +1,7 @@
 from typing import *
 
+from atomicwrites import atomic_write
+
 from corrscope.config import DumpableAttrs, yaml
 from corrscope.settings import paths
 
@@ -50,4 +52,5 @@ def load_prefs() -> GlobalPrefs:
 
 
 def dump_prefs(pref: GlobalPrefs) -> None:
-    yaml.dump(pref, _PREF_PATH)
+    with atomic_write(_PREF_PATH, overwrite=True) as f:
+        yaml.dump(pref, f)

poetry.lock

@@ -18,7 +18,7 @@ python-versions = "*"
 name = "atomicwrites"
 version = "1.4.0"
 description = "Atomic file writes."
-category = "dev"
+category = "main"
 optional = false
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
@@ -609,7 +609,7 @@ testing = ["pytest (>=4.6)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pyt
 [metadata]
 lock-version = "1.1"
 python-versions = "^3.6.2"
-content-hash = "7e4bd31660cb4764c68a7f51487837972530c1426c7902c04ca760d5ef278fa5"
+content-hash = "bb03d24e8ec7fcbf38ca0726736a7cdcd3e3f38a2ad281f522e3aedce1540bfb"
 
 [metadata.files]
 altgraph = [

pyproject.toml

@@ -27,6 +27,7 @@ matplotlib = "^3.1"
 attrs = "^21.2.0"
 PyQt5 = "^5.15.4"
 appdirs = "^1.4.4"
+atomicwrites = "^1.4.0"
 
 [tool.poetry.dev-dependencies]
 pytest = "^6.2.4"