[red-knot] Rename FileSystem to System (#12214)

crates/ruff_db/src/system.rs

@@ -0,0 +1,97 @@
+pub use memory_fs::MemoryFileSystem;
+pub use os::OsSystem;
+pub use test::{DbWithTestSystem, TestSystem};
+
+use crate::file_revision::FileRevision;
+
+pub use self::path::{SystemPath, SystemPathBuf};
+
+mod memory_fs;
+mod os;
+mod path;
+mod test;
+
+pub type Result<T> = std::io::Result<T>;
+
+/// The system on which Ruff runs.
+///
+/// Ruff supports running on the CLI, in a language server, and in a browser (WASM). Each of these
+/// host-systems differ in what system operations they support and how they interact with the file system:
+/// * Language server:
+///    * Reading a file's content should take into account that it might have unsaved changes because it's open in the editor.
+///    * Use structured representations for notebooks, making deserializing a notebook from a string unnecessary.
+///    * Use their own file watching infrastructure.
+/// * WASM (Browser):
+///    * There are ways to emulate a file system in WASM but a native memory-filesystem is more efficient.
+///    * Doesn't support a current working directory
+///    * File watching isn't supported.
+///
+/// Abstracting the system also enables tests to use a more efficient in-memory file system.
+pub trait System {
+    /// Reads the metadata of the file or directory at `path`.
+    fn path_metadata(&self, path: &SystemPath) -> Result<Metadata>;
+
+    /// Reads the content of the file at `path` into a [`String`].
+    fn read_to_string(&self, path: &SystemPath) -> Result<String>;
+
+    /// Returns `true` if `path` exists.
+    fn path_exists(&self, path: &SystemPath) -> bool {
+        self.path_metadata(path).is_ok()
+    }
+
+    /// Returns `true` if `path` exists and is a directory.
+    fn is_directory(&self, path: &SystemPath) -> bool {
+        self.path_metadata(path)
+            .map_or(false, |metadata| metadata.file_type.is_directory())
+    }
+
+    /// Returns `true` if `path` exists and is a file.
+    fn is_file(&self, path: &SystemPath) -> bool {
+        self.path_metadata(path)
+            .map_or(false, |metadata| metadata.file_type.is_file())
+    }
+
+    fn as_any(&self) -> &dyn std::any::Any;
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Metadata {
+    revision: FileRevision,
+    permissions: Option<u32>,
+    file_type: FileType,
+}
+
+impl Metadata {
+    pub fn revision(&self) -> FileRevision {
+        self.revision
+    }
+
+    pub fn permissions(&self) -> Option<u32> {
+        self.permissions
+    }
+
+    pub fn file_type(&self) -> FileType {
+        self.file_type
+    }
+}
+
+#[derive(Copy, Clone, Eq, PartialEq, Debug, Hash)]
+pub enum FileType {
+    File,
+    Directory,
+    Symlink,
+}
+
+impl FileType {
+    pub const fn is_file(self) -> bool {
+        matches!(self, FileType::File)
+    }
+
+    pub const fn is_directory(self) -> bool {
+        matches!(self, FileType::Directory)
+    }
+
+    pub const fn is_symlink(self) -> bool {
+        matches!(self, FileType::Symlink)
+    }
+}