refactor(tvix/eval): impl Default for SourceCode

… instead of new(). Suggested by clippy.

Change-Id: Iac7be733392afefc2b4ff2e38386eee95f3bce94
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9103
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/eval/src/source.rs

@@ -19,11 +19,6 @@ use codemap::{CodeMap, Span};
 pub struct SourceCode(Rc<RefCell<CodeMap>>);
 
 impl SourceCode {
-    /// Create a new SourceCode instance.
-    pub fn new() -> Self {
-        SourceCode(Rc::new(RefCell::new(CodeMap::new())))
-    }
-
     /// Access a read-only reference to the codemap.
     pub fn codemap(&self) -> Ref<CodeMap> {
         self.0.borrow()
@@ -61,3 +56,10 @@ impl SourceCode {
         self.codemap().look_up_span(span).file
     }
 }
+
+impl Default for SourceCode {
+    /// Create a new SourceCode instance.
+    fn default() -> Self {
+        Self(Rc::new(RefCell::new(CodeMap::new())))
+    }
+}