workspace: Add restore_on_startup setting that allows always opening an empty Zed instance (#10366)

Fixes #7694
The new setting accepts "last_workspace" (default) and "none" as
options.

In a follow-up PR I'll add a new option that re-launches all of the Zed
windows and not just the last one.

Release Notes:

- Added `restore_on_startup` option, accepting `last_workspace`
(default) and `none` options. With `none`, new Zed instances will not
restore workspaces that were open last.

crates/workspace/src/workspace.rs

@@ -81,7 +81,9 @@ use ui::{
 };
 use util::ResultExt;
 use uuid::Uuid;
-pub use workspace_settings::{AutosaveSetting, TabBarSettings, WorkspaceSettings};
+pub use workspace_settings::{
+    AutosaveSetting, RestoreOnStartupBehaviour, TabBarSettings, WorkspaceSettings,
+};
 
 use crate::notifications::NotificationId;
 use crate::persistence::{

crates/workspace/src/workspace_settings.rs

@@ -10,6 +10,17 @@ pub struct WorkspaceSettings {
     pub confirm_quit: bool,
     pub show_call_status_icon: bool,
     pub autosave: AutosaveSetting,
+    pub restore_on_startup: RestoreOnStartupBehaviour,
+}
+
+#[derive(Copy, Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum RestoreOnStartupBehaviour {
+    /// Always start with an empty editor
+    None,
+    /// Restore the workspace that was closed last.
+    #[default]
+    LastWorkspace,
 }
 
 #[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
@@ -32,6 +43,10 @@ pub struct WorkspaceSettingsContent {
     ///
     /// Default: off
     pub autosave: Option<AutosaveSetting>,
+    /// Controls previous session restoration in freshly launched Zed instance.
+    /// Values: none, last_workspace
+    /// Default: last_workspace
+    pub restore_on_startup: Option<RestoreOnStartupBehaviour>,
 }
 
 #[derive(Deserialize)]