fix: write scraped files whole or not at all

scripts/artifacts.py

@@ -60,7 +60,7 @@ def write_text_atomic(path: str, content: str) -> None:
         dir=directory, prefix=f".{os.path.basename(path)}.", suffix=".tmp"
     )
     try:
-        with os.fdopen(handle, "w") as f:
+        with os.fdopen(handle, "w", encoding="utf-8") as f:
             f.write(content)
         os.replace(scratch, path)
     except BaseException:

scripts/scraper/_hash_merge.py

@@ -14,7 +14,7 @@ from pathlib import Path
 from typing import Any
 
 
-from common import yaml_load
+from common import write_text_atomic, yaml_load
 
 
 _MAME_RELEASE_RE = re.compile(r"^0\.\d+")
@@ -390,7 +390,7 @@ def _backup_and_write(path: str, data: dict) -> None:
     patched = _patch_bios_entries(patched, data.get("files", []))
     patched = _append_new_entries(patched, data.get("files", []), original)
 
-    p.write_text(patched, encoding="utf-8")
+    write_text_atomic(str(p), patched)
 
 
 def _patch_core_version(text: str, version: str) -> str:
@@ -606,4 +606,4 @@ def _backup_and_write_fbneo(path: str, data: dict, hashes: dict) -> None:
             lines.append("")
         patched = patched.rstrip("\n") + "\n\n" + "\n".join(lines)
 
-    p.write_text(patched, encoding="utf-8")
+    write_text_atomic(str(p), patched)

scripts/scraper/base_scraper.py

@@ -12,7 +12,7 @@ import yaml
 from abc import ABC, abstractmethod
 from dataclasses import dataclass, field
 from pathlib import Path
-from common import yaml_load
+from common import write_text_atomic, yaml_load
 
 
 @dataclass
@@ -373,11 +373,12 @@ def scraper_cli(
                 for field in ("data_directories",):
                     if field in old_sys and field not in sys_data:
                         sys_data[field] = old_sys[field]
-        with open(output_path, "w") as f:
-            yaml.dump(
-                config, f, Dumper=_PlatformDumper,
-                default_flow_style=False, allow_unicode=True, sort_keys=False,
-            )
+        # Written whole or not at all: a reader in the middle of a streamed
+        # dump parsed a valid platform with a fraction of its systems.
+        write_text_atomic(output_path, yaml.dump(
+            config, Dumper=_PlatformDumper,
+            default_flow_style=False, allow_unicode=True, sort_keys=False,
+        ))
         print(f"Written {len(reqs)} entries to {args.output}")
         return
 

scripts/scraper/fbneo_hash_scraper.py

@@ -20,7 +20,7 @@ from typing import Any
 
 import yaml
 
-from common import yaml_load
+from common import write_text_atomic, yaml_load
 
 from scripts.scraper._hash_merge import compute_diff, merge_fbneo_profile
 from scripts.scraper.fbneo_parser import parse_fbneo_source_tree
@@ -187,9 +187,8 @@ def fetch_and_cache(force: bool = False) -> dict[str, Any]:
         }
 
         CACHE_PATH.parent.mkdir(parents=True, exist_ok=True)
-        CACHE_PATH.write_text(
-            json.dumps(cache, indent=2, ensure_ascii=False) + "\n",
-            encoding="utf-8",
+        write_text_atomic(
+            str(CACHE_PATH), json.dumps(cache, indent=2, ensure_ascii=False) + "\n"
         )
         log.info("wrote %d BIOS sets to %s", len(bios_sets), CACHE_PATH)
 

scripts/scraper/mame_hash_scraper.py

@@ -22,7 +22,7 @@ from typing import Any
 
 import yaml
 
-from common import yaml_load
+from common import write_text_atomic, yaml_load
 
 from ._hash_merge import compute_diff, merge_mame_profile
 from .mame_parser import parse_mame_source_tree
@@ -66,8 +66,9 @@ def _is_stale(cache: dict[str, Any] | None) -> bool:
 
 def _write_cache(data: dict[str, Any]) -> None:
     _CACHE_PATH.parent.mkdir(parents=True, exist_ok=True)
-    with open(_CACHE_PATH, "w", encoding="utf-8") as f:
-        json.dump(data, f, indent=2, ensure_ascii=False)
+    write_text_atomic(
+        str(_CACHE_PATH), json.dumps(data, indent=2, ensure_ascii=False)
+    )
     log.info("cache written to %s", _CACHE_PATH)
 
 

scripts/scraper/targets/__init__.py

@@ -28,8 +28,11 @@ class BaseTargetScraper(ABC):
             import yaml
         except ImportError:
             raise ImportError("PyYAML required: pip install pyyaml")
-        with open(output_path, "w") as f:
-            yaml.dump(data, f, default_flow_style=False, sort_keys=False)
+        from common import write_text_atomic
+
+        write_text_atomic(
+            output_path, yaml.dump(data, default_flow_style=False, sort_keys=False)
+        )
 
 
 _scrapers: dict[str, type] = {}

tests/test_atomic_artifacts.py

@@ -65,5 +65,33 @@ class EveryWriterGoesThroughIt(unittest.TestCase):
         self.assertNotIn("shutil.copy2(source, path)", (scripts / "restore_large_files.py").read_text())
 
 
+    def test_scrapers_write_whole_files(self):
+        """A streamed yaml.dump into platforms/<x>.yml let a concurrent reader
+        parse a valid platform holding a fraction of its systems."""
+        import re
+
+        streamed = re.compile(
+            r"open\([^)]*['\"](?:w|wb|a)['\"]|\.write_text\(|\.write_bytes\("
+        )
+        offenders = [
+            f"{path.relative_to(REPO_ROOT)}:{number}"
+            for path in sorted((REPO_ROOT / "scripts" / "scraper").rglob("*.py"))
+            for number, line in enumerate(
+                path.read_text(encoding="utf-8").splitlines(), 1
+            )
+            if streamed.search(line)
+        ]
+        self.assertEqual(offenders, [])
+
+    def test_the_text_is_utf8_whatever_the_locale(self):
+        import tempfile
+
+        with tempfile.TemporaryDirectory() as directory:
+            target = Path(directory) / "out.yml"
+            artifacts.write_text_atomic(str(target), "name: \u00e9mulateur \u2014 \u30d5\n")
+            self.assertEqual(
+                target.read_bytes().decode("utf-8"), "name: \u00e9mulateur \u2014 \u30d5\n"
+            )
+
 if __name__ == "__main__":
     unittest.main()