Add --ephemeral cli flag

src/main.rs

@@ -61,28 +61,41 @@ struct Args {
     /// Path to a directory for cove to store its data in.
     #[clap(long, short)]
     data_dir: Option<PathBuf>,
+
+    /// If set, cove won't store data permanently.
+    #[clap(long, short, action)]
+    ephemeral: bool,
+
     /// Measure the width of characters as displayed by the terminal emulator
     /// instead of guessing the width.
     #[clap(long, short, action)]
     measure_widths: bool,
+
     #[clap(subcommand)]
     command: Option<Command>,
 }
 
+fn data_dir(args_data_dir: Option<PathBuf>) -> PathBuf {
+    if let Some(data_dir) = args_data_dir {
+        data_dir
+    } else {
+        let dirs =
+            ProjectDirs::from("de", "plugh", "cove").expect("unable to determine directories");
+        dirs.data_dir().to_path_buf()
+    }
+}
+
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
     let args = Args::parse();
 
-    let data_dir = if let Some(data_dir) = args.data_dir {
-        data_dir
+    let vault = if args.ephemeral {
+        vault::launch_in_memory()?
     } else {
-        let dirs =
-            ProjectDirs::from("de", "plugh", "cove").expect("unable to determine directories");
-        dirs.data_dir().to_path_buf()
+        let data_dir = data_dir(args.data_dir);
+        println!("Data dir: {}", data_dir.to_string_lossy());
+        vault::launch(&data_dir.join("vault.db"))?
     };
-    println!("Data dir: {}", data_dir.to_string_lossy());
-
-    let vault = vault::launch(&data_dir.join("vault.db"))?;
 
     match args.command.unwrap_or_default() {
         Command::Run => run(&vault, args.measure_widths).await?,

src/vault.rs

@@ -20,9 +20,14 @@ enum Request {
 #[derive(Debug, Clone)]
 pub struct Vault {
     tx: mpsc::UnboundedSender<Request>,
+    ephemeral: bool,
 }
 
 impl Vault {
+    pub fn ephemeral(&self) -> bool {
+        self.ephemeral
+    }
+
     pub async fn close(&self) {
         let (tx, rx) = oneshot::channel();
         let _ = self.tx.send(Request::Close(tx));
@@ -64,12 +69,26 @@ fn run(mut conn: Connection, mut rx: mpsc::UnboundedReceiver<Request>) {
     }
 }
 
+fn launch_from_connection(mut conn: Connection, ephemeral: bool) -> rusqlite::Result<Vault> {
+    conn.pragma_update(None, "foreign_keys", true)?;
+    conn.pragma_update(None, "trusted_schema", false)?;
+
+    println!("Opening vault");
+
+    migrate::migrate(&mut conn)?;
+    prepare::prepare(&mut conn)?;
+
+    let (tx, rx) = mpsc::unbounded_channel();
+    thread::spawn(move || run(conn, rx));
+    Ok(Vault { tx, ephemeral })
+}
+
 pub fn launch(path: &Path) -> rusqlite::Result<Vault> {
     // If this fails, rusqlite will complain about not being able to open the db
     // file, which saves me from adding a separate vault error type.
     let _ = fs::create_dir_all(path.parent().expect("path to file"));
 
-    let mut conn = Connection::open(path)?;
+    let conn = Connection::open(path)?;
 
     // Setting locking mode before journal mode so no shared memory files
     // (*-shm) need to be created by sqlite. Apparently, setting the journal
@@ -78,13 +97,11 @@ pub fn launch(path: &Path) -> rusqlite::Result<Vault> {
     // https://sqlite.org/pragma.html#pragma_locking_mode
     conn.pragma_update(None, "locking_mode", "exclusive")?;
     conn.pragma_update(None, "journal_mode", "wal")?;
-    conn.pragma_update(None, "foreign_keys", true)?;
-    conn.pragma_update(None, "trusted_schema", false)?;
 
-    migrate::migrate(&mut conn)?;
-    prepare::prepare(&mut conn)?;
-
-    let (tx, rx) = mpsc::unbounded_channel();
-    thread::spawn(move || run(conn, rx));
-    Ok(Vault { tx })
+    launch_from_connection(conn, false)
+}
+
+pub fn launch_in_memory() -> rusqlite::Result<Vault> {
+    let conn = Connection::open_in_memory()?;
+    launch_from_connection(conn, true)
 }

src/vault/prepare.rs

@@ -1,8 +1,6 @@
 use rusqlite::Connection;
 
 pub fn prepare(conn: &mut Connection) -> rusqlite::Result<()> {
-    println!("Opening vault");
-
     // Cache ids of tree roots.
     conn.execute_batch(
         "