Add CACHEDIR.TAG to .ruff_cache (#830)

Cargo.lock

@@ -397,6 +397,15 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c1db59621ec70f09c5e9b597b220c7a2b43611f4710dc03ceb8748637775692c"
 
+[[package]]
+name = "cachedir"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e236bf5873ea57ec2877445297f4da008916bfae51567131acfc54a073d694f3"
+dependencies = [
+ "tempfile",
+]
+
 [[package]]
 name = "cast"
 version = "0.3.0"
@@ -2257,6 +2266,7 @@ dependencies = [
  "bincode",
  "bitflags",
  "cacache",
+ "cachedir",
  "chrono",
  "clap 4.0.22",
  "clearscreen",

Cargo.toml

@@ -18,6 +18,7 @@ anyhow = { version = "1.0.66" }
 atty = { version = "0.2.14" }
 bincode = { version = "1.3.3" }
 bitflags = { version = "1.3.2" }
+cachedir = { version = "0.3.0" }
 chrono = { version = "0.4.21", default-features = false, features = ["clock"] }
 clap = { version = "4.0.1", features = ["derive"] }
 colored = { version = "2.0.0" }

src/cache.rs

@@ -94,16 +94,29 @@ fn cache_key(path: &Path, settings: &Settings, autofix: &fixer::Mode) -> String
     )
 }
 
+/// Initialize the cache directory.
 pub fn init() -> Result<()> {
-    let gitignore_path = Path::new(cache_dir()).join(".gitignore");
-    if gitignore_path.exists() {
-        return Ok(());
+    let path = Path::new(cache_dir());
+
+    // Create the directory.
+    create_dir_all(path)?;
+
+    // Add the CACHEDIR.TAG.
+    if !cachedir::is_tagged(path)? {
+        cachedir::add_tag(path)?;
     }
-    create_dir_all(cache_dir())?;
-    let mut file = File::create(gitignore_path)?;
-    file.write_all(b"*").map_err(|e| e.into())
+
+    // Add the .gitignore.
+    let gitignore_path = path.join(".gitignore");
+    if !gitignore_path.exists() {
+        let mut file = File::create(gitignore_path)?;
+        file.write_all(b"*")?;
+    }
+
+    Ok(())
 }
 
+/// Get a value from the cache.
 pub fn get(
     path: &Path,
     metadata: &Metadata,
@@ -134,6 +147,7 @@ pub fn get(
     None
 }
 
+/// Set a value in the cache.
 pub fn set(
     path: &Path,
     metadata: &Metadata,