Make missing scale = automatic selection

That was the intention, but I missed it before.

niri-config/src/lib.rs

@@ -243,8 +243,8 @@ pub struct Output {
     pub off: bool,
     #[knuffel(argument)]
     pub name: String,
-    #[knuffel(child, unwrap(argument), default = 1.)]
+    #[knuffel(child, unwrap(argument))]
-    pub scale: f64,
+    pub scale: Option<f64>,
     #[knuffel(child, unwrap(argument, str), default = Transform::Normal)]
     pub transform: Transform,
     #[knuffel(child)]
@@ -260,7 +260,7 @@ impl Default for Output {
         Self {
             off: false,
             name: String::new(),
-            scale: 1.,
+            scale: None,
             transform: Transform::Normal,
             position: None,
             mode: None,
@@ -2291,7 +2291,7 @@ mod tests {
                 outputs: vec![Output {
                     off: false,
                     name: "eDP-1".to_owned(),
-                    scale: 2.,
+                    scale: Some(2.),
                     transform: Transform::Flipped90,
                     position: Some(Position { x: 10, y: 20 }),
                     mode: Some(ConfiguredMode {

niri-ipc/src/lib.rs

@@ -278,9 +278,9 @@ pub enum OutputAction {
     },
     /// Set the output scale.
     Scale {
-        /// Scale factor to set.
+        /// Scale factor to set, or "auto" for automatic selection.
         #[cfg_attr(feature = "clap", arg())]
-        scale: f64,
+        scale: ScaleToSet,
     },
     /// Set the output transform.
     Transform {
@@ -329,6 +329,15 @@ pub struct ConfiguredMode {
     pub refresh: Option<f64>,
 }
 
+/// Output scale to set.
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq)]
+pub enum ScaleToSet {
+    /// Niri will pick the scale automatically.
+    Automatic,
+    /// Specific scale.
+    Specific(f64),
+}
+
 /// Output position to set.
 #[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq)]
 #[cfg_attr(feature = "clap", derive(clap::Subcommand))]
@@ -560,3 +569,16 @@ impl FromStr for ConfiguredMode {
         })
     }
 }
+
+impl FromStr for ScaleToSet {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if s.eq_ignore_ascii_case("auto") {
+            return Ok(Self::Automatic);
+        }
+
+        let scale = s.parse().map_err(|_| "error parsing scale")?;
+        Ok(Self::Specific(scale))
+    }
+}

src/niri.rs

@@ -1014,7 +1014,7 @@ impl State {
             let config = self.niri.config.borrow_mut();
             let config = config.outputs.iter().find(|o| o.name == name);
 
-            let scale = config.map(|c| c.scale).unwrap_or_else(|| {
+            let scale = config.and_then(|c| c.scale).unwrap_or_else(|| {
                 let size_mm = output.physical_properties().size;
                 let resolution = output.current_mode().unwrap().size;
                 guess_monitor_scale(size_mm, resolution)
@@ -1077,7 +1077,12 @@ impl State {
                         niri_ipc::ModeToSet::Specific(mode) => Some(mode),
                     }
                 }
-                niri_ipc::OutputAction::Scale { scale } => config.scale = scale,
+                niri_ipc::OutputAction::Scale { scale } => {
+                    config.scale = match scale {
+                        niri_ipc::ScaleToSet::Automatic => None,
+                        niri_ipc::ScaleToSet::Specific(scale) => Some(scale),
+                    }
+                }
                 niri_ipc::OutputAction::Transform { transform } => config.transform = transform,
                 niri_ipc::OutputAction::Position { position } => {
                     config.position = match position {
@@ -1666,7 +1671,7 @@ impl Niri {
 
         let config = self.config.borrow();
         let c = config.outputs.iter().find(|o| o.name == name);
-        let scale = c.map(|c| c.scale).unwrap_or_else(|| {
+        let scale = c.and_then(|c| c.scale).unwrap_or_else(|| {
             let size_mm = output.physical_properties().size;
             let resolution = output.current_mode().unwrap().size;
             guess_monitor_scale(size_mm, resolution)