init

.venv/lib/python3.8/site-packages/mypy/fswatcher.py

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+"""Watch parts of the file system for changes."""
+
+from mypy.fscache import FileSystemCache
+from typing import AbstractSet, Dict, Iterable, List, NamedTuple, Optional, Set, Tuple
+
+
+FileData = NamedTuple('FileData', [('st_mtime', float),
+                                   ('st_size', int),
+                                   ('hash', str)])
+
+
+class FileSystemWatcher:
+    """Watcher for file system changes among specific paths.
+
+    All file system access is performed using FileSystemCache. We
+    detect changed files by stat()ing them all and comparing hashes
+    of potentially changed files. If a file has both size and mtime
+    unmodified, the file is assumed to be unchanged.
+
+    An important goal of this class is to make it easier to eventually
+    use file system events to detect file changes.
+
+    Note: This class doesn't flush the file system cache. If you don't
+    manually flush it, changes won't be seen.
+    """
+
+    # TODO: Watching directories?
+    # TODO: Handle non-files
+
+    def __init__(self, fs: FileSystemCache) -> None:
+        self.fs = fs
+        self._paths: Set[str] = set()
+        self._file_data: Dict[str, Optional[FileData]] = {}
+
+    def dump_file_data(self) -> Dict[str, Tuple[float, int, str]]:
+        return {k: v for k, v in self._file_data.items() if v is not None}
+
+    def set_file_data(self, path: str, data: FileData) -> None:
+        self._file_data[path] = data
+
+    def add_watched_paths(self, paths: Iterable[str]) -> None:
+        for path in paths:
+            if path not in self._paths:
+                # By storing None this path will get reported as changed by
+                # find_changed if it exists.
+                self._file_data[path] = None
+        self._paths |= set(paths)
+
+    def remove_watched_paths(self, paths: Iterable[str]) -> None:
+        for path in paths:
+            if path in self._file_data:
+                del self._file_data[path]
+        self._paths -= set(paths)
+
+    def _update(self, path: str) -> None:
+        st = self.fs.stat(path)
+        hash_digest = self.fs.hash_digest(path)
+        self._file_data[path] = FileData(st.st_mtime, st.st_size, hash_digest)
+
+    def _find_changed(self, paths: Iterable[str]) -> AbstractSet[str]:
+        changed = set()
+        for path in paths:
+            old = self._file_data[path]
+            try:
+                st = self.fs.stat(path)
+            except FileNotFoundError:
+                if old is not None:
+                    # File was deleted.
+                    changed.add(path)
+                    self._file_data[path] = None
+            else:
+                if old is None:
+                    # File is new.
+                    changed.add(path)
+                    self._update(path)
+                # Round mtimes down, to match the mtimes we write to meta files
+                elif st.st_size != old.st_size or int(st.st_mtime) != int(old.st_mtime):
+                    # Only look for changes if size or mtime has changed as an
+                    # optimization, since calculating hash is expensive.
+                    new_hash = self.fs.hash_digest(path)
+                    self._update(path)
+                    if st.st_size != old.st_size or new_hash != old.hash:
+                        # Changed file.
+                        changed.add(path)
+        return changed
+
+    def find_changed(self) -> AbstractSet[str]:
+        """Return paths that have changes since the last call, in the watched set."""
+        return self._find_changed(self._paths)
+
+    def update_changed(self,
+                       remove: List[str],
+                       update: List[str],
+                       ) -> AbstractSet[str]:
+        """Alternative to find_changed() given explicit changes.
+
+        This only calls self.fs.stat() on added or updated files, not
+        on all files.  It believes all other files are unchanged!
+
+        Implies add_watched_paths() for add and update, and
+        remove_watched_paths() for remove.
+        """
+        self.remove_watched_paths(remove)
+        self.add_watched_paths(update)
+        return self._find_changed(update)