refactor(const): Mark low level fns const

Mark functions of `structs` that suit themselves to be composed as const,
namely:

- `Block`
- `Layout`
- `Rect`

Continuation of: ratatui#115

src/layout.rs

@@ -107,30 +107,30 @@ impl Layout {
         self
     }
 
-    pub fn margin(mut self, margin: u16) -> Layout {
+    pub const fn margin(mut self, margin: u16) -> Layout {
         self.margin = Margin {
             horizontal: margin,
             vertical: margin,
         };
         self
     }
 
-    pub fn horizontal_margin(mut self, horizontal: u16) -> Layout {
+    pub const fn horizontal_margin(mut self, horizontal: u16) -> Layout {
         self.margin.horizontal = horizontal;
         self
     }
 
-    pub fn vertical_margin(mut self, vertical: u16) -> Layout {
+    pub const fn vertical_margin(mut self, vertical: u16) -> Layout {
         self.margin.vertical = vertical;
         self
     }
 
-    pub fn direction(mut self, direction: Direction) -> Layout {
+    pub const fn direction(mut self, direction: Direction) -> Layout {
         self.direction = direction;
         self
     }
 
-    pub(crate) fn expand_to_fill(mut self, expand_to_fill: bool) -> Layout {
+    pub(crate) const fn expand_to_fill(mut self, expand_to_fill: bool) -> Layout {
         self.expand_to_fill = expand_to_fill;
         self
     }
@@ -422,23 +422,23 @@ impl Rect {
         }
     }
 
-    pub fn area(self) -> u16 {
+    pub const fn area(self) -> u16 {
         self.width * self.height
     }
 
-    pub fn left(self) -> u16 {
+    pub const fn left(self) -> u16 {
         self.x
     }
 
-    pub fn right(self) -> u16 {
+    pub const fn right(self) -> u16 {
         self.x.saturating_add(self.width)
     }
 
-    pub fn top(self) -> u16 {
+    pub const fn top(self) -> u16 {
         self.y
     }
 
-    pub fn bottom(self) -> u16 {
+    pub const fn bottom(self) -> u16 {
         self.y.saturating_add(self.height)
     }
 
@@ -481,7 +481,7 @@ impl Rect {
         }
     }
 
-    pub fn intersects(self, other: Rect) -> bool {
+    pub const fn intersects(self, other: Rect) -> bool {
         self.x < other.x + other.width
             && self.x + self.width > other.x
             && self.y < other.y + other.height

src/widgets/block.rs

@@ -19,7 +19,7 @@ pub enum BorderType {
 }
 
 impl BorderType {
-    pub fn line_symbols(border_type: BorderType) -> line::Set {
+    pub const fn line_symbols(border_type: BorderType) -> line::Set {
         match border_type {
             BorderType::Plain => line::NORMAL,
             BorderType::Rounded => line::ROUNDED,
@@ -38,7 +38,7 @@ pub struct Padding {
 }
 
 impl Padding {
-    pub fn new(left: u16, right: u16, top: u16, bottom: u16) -> Self {
+    pub const fn new(left: u16, right: u16, top: u16, bottom: u16) -> Self {
         Padding {
             left,
             right,
@@ -47,7 +47,7 @@ impl Padding {
         }
     }
 
-    pub fn zero() -> Self {
+    pub const fn zero() -> Self {
         Padding {
             left: 0,
             right: 0,
@@ -56,7 +56,7 @@ impl Padding {
         }
     }
 
-    pub fn horizontal(value: u16) -> Self {
+    pub const fn horizontal(value: u16) -> Self {
         Padding {
             left: value,
             right: value,
@@ -65,7 +65,7 @@ impl Padding {
         }
     }
 
-    pub fn vertical(value: u16) -> Self {
+    pub const fn vertical(value: u16) -> Self {
         Padding {
             left: 0,
             right: 0,
@@ -74,7 +74,7 @@ impl Padding {
         }
     }
 
-    pub fn uniform(value: u16) -> Self {
+    pub const fn uniform(value: u16) -> Self {
         Padding {
             left: value,
             right: value,
@@ -192,7 +192,7 @@ impl<'a> Block<'a> {
     }
 
     /// Applies the style to all titles. If a title already has a style, it will add on top of it.
-    pub fn title_style(mut self, style: Style) -> Block<'a> {
+    pub const fn title_style(mut self, style: Style) -> Block<'a> {
         self.titles_style = style;
         self
     }
@@ -210,7 +210,7 @@ impl<'a> Block<'a> {
     ///   .title("bar")
     ///   .title_alignment(Alignment::Center);
     /// ```
-    pub fn title_alignment(mut self, alignment: Alignment) -> Block<'a> {
+    pub const fn title_alignment(mut self, alignment: Alignment) -> Block<'a> {
         self.titles_alignment = alignment;
         self
     }
@@ -233,27 +233,27 @@ impl<'a> Block<'a> {
     ///   .title("bar")
     ///   .title_position(Position::Bottom);
     /// ```
-    pub fn title_position(mut self, position: Position) -> Block<'a> {
+    pub const fn title_position(mut self, position: Position) -> Block<'a> {
         self.titles_position = position;
         self
     }
 
-    pub fn border_style(mut self, style: Style) -> Block<'a> {
+    pub const fn border_style(mut self, style: Style) -> Block<'a> {
         self.border_style = style;
         self
     }
 
-    pub fn style(mut self, style: Style) -> Block<'a> {
+    pub const fn style(mut self, style: Style) -> Block<'a> {
         self.style = style;
         self
     }
 
-    pub fn borders(mut self, flag: Borders) -> Block<'a> {
+    pub const fn borders(mut self, flag: Borders) -> Block<'a> {
         self.borders = flag;
         self
     }
 
-    pub fn border_type(mut self, border_type: BorderType) -> Block<'a> {
+    pub const fn border_type(mut self, border_type: BorderType) -> Block<'a> {
         self.border_type = border_type;
         self
     }
@@ -317,7 +317,7 @@ impl<'a> Block<'a> {
         inner
     }
 
-    pub fn padding(mut self, padding: Padding) -> Block<'a> {
+    pub const fn padding(mut self, padding: Padding) -> Block<'a> {
         self.padding = padding;
         self
     }