Fix Clippy warnings

Makefile

@@ -85,6 +85,7 @@ test: $(TEST_EXE)
 	@echo "$(TEST_EXE)" | awk '{ OFS="\n"; $$1=$$1 } 1' | /bin/sh
 	$(CARGO) test
 	$(CARGO) fmt --check
+	$(CARGO) clippy
 
 clean:
 	rm -f $(ALL_OBJ) $(ALL_EXE)

src/api/settings.rs

@@ -105,10 +105,7 @@ unsafe extern "C" fn settings_set_master_area_factor_per_unit(value: c_uchar) {
 
 #[no_mangle]
 unsafe extern "C" fn settings_get_max_clients_in_master() -> c_int {
-    match SETTINGS.unwrap().max_clients_in_master() {
-        None => 0,
-        Some(value) => value,
-    }
+    SETTINGS.unwrap().max_clients_in_master().unwrap_or(0)
 }
 
 #[no_mangle]

src/settings.rs

@@ -86,13 +86,13 @@ impl Default for ForSingleWindow {
     }
 }
 
-impl Into<c_uchar> for ForSingleWindow {
-    fn into(self) -> c_uchar {
-        match self {
-            Self::Never => 0,
-            Self::Always => 1,
-            Self::NotInFullscreen => 2,
-            Self::NobodyIsFullscreen => 3,
+impl From<ForSingleWindow> for c_uchar {
+    fn from(value: ForSingleWindow) -> Self {
+        match value {
+            ForSingleWindow::Never => 0,
+            ForSingleWindow::Always => 1,
+            ForSingleWindow::NotInFullscreen => 2,
+            ForSingleWindow::NobodyIsFullscreen => 3,
         }
     }
 }
@@ -176,7 +176,7 @@ impl Settings {
     // TODO: notify WM to rearrange clients
     pub fn max_clients_in_master_set(&mut self, value: Option<c_int>) {
         self.max_clients_in_master =
-            value.map(|value| constraints::max_clients_in_master(value));
+            value.map(constraints::max_clients_in_master);
     }
 
     pub fn respect_resize_hints_in_floating_layout(&self) -> bool {

src/unit.rs

@@ -7,12 +7,12 @@ pub enum Kind {
     Tag,
 }
 
-impl Into<c_uchar> for Kind {
-    fn into(self) -> c_uchar {
-        match self {
-            Self::Global => 0,
-            Self::Monitor => 1,
-            Self::Tag => 2,
+impl From<Kind> for c_uchar {
+    fn from(value: Kind) -> Self {
+        match value {
+            Kind::Global => 0,
+            Kind::Monitor => 1,
+            Kind::Tag => 2,
         }
     }
 }