Fix a few nursery rule violations (#2548)

src/source_code/generator.rs

@@ -57,8 +57,12 @@ impl<'a> From<&'a Stylist<'a>> for Generator<'a> {
 }
 
 impl<'a> Generator<'a> {
-    pub fn new(indent: &'a Indentation, quote: &'a Quote, line_ending: &'a LineEnding) -> Self {
-        Generator {
+    pub const fn new(
+        indent: &'a Indentation,
+        quote: &'a Quote,
+        line_ending: &'a LineEnding,
+    ) -> Self {
+        Self {
             // Style preferences.
             indent,
             quote,

src/source_code/locator.rs

@@ -93,8 +93,8 @@ fn truncate(location: Location, index: &Index, contents: &str) -> usize {
 }
 
 impl<'a> Locator<'a> {
-    pub fn new(contents: &'a str) -> Self {
-        Locator {
+    pub const fn new(contents: &'a str) -> Self {
+        Self {
             contents,
             index: OnceCell::new(),
         }
@@ -140,11 +140,11 @@ impl<'a> Locator<'a> {
         )
     }
 
-    pub fn len(&self) -> usize {
+    pub const fn len(&self) -> usize {
         self.contents.len()
     }
 
-    pub fn is_empty(&self) -> bool {
+    pub const fn is_empty(&self) -> bool {
         self.contents.is_empty()
     }
 }

src/source_code/stylist.rs

@@ -97,7 +97,7 @@ impl From<&Quote> for char {
 pub struct Indentation(String);
 
 impl Indentation {
-    pub fn new(indentation: String) -> Self {
+    pub const fn new(indentation: String) -> Self {
         Self(indentation)
     }
 }
@@ -142,7 +142,7 @@ impl Default for LineEnding {
 }
 
 impl LineEnding {
-    pub fn as_str(&self) -> &'static str {
+    pub const fn as_str(&self) -> &'static str {
         match self {
             LineEnding::CrLf => "\r\n",
             LineEnding::Lf => "\n",