Fix and work around excessively strict dead_code lint in Rust 1.78 nightly

See rust-lang/rust#120770

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/927>

Author: amyspark

rsvg/src/float_eq_cairo.rs

@@ -29,6 +29,7 @@ fn cairo_fixed_from_double(d: f64) -> i32 {
 /// the integral part, and 8 bits for the fractional part.  That is,
 /// the smallest fraction they can represent is 1/256.
 pub trait FixedEqCairo {
+    #[allow(dead_code)] // https://github.com/rust-lang/rust/issues/120770
     fn fixed_eq_cairo(&self, other: &Self) -> bool;
 }
 

rsvg_convert/src/main.rs

@@ -1232,33 +1232,6 @@ fn parse_zoom_factor(v: &str) -> Result<ZoomFactor, String> {
     }
 }
 
-trait NotFound {
-    type Ok;
-    type Error;
-
-    fn or_none(self) -> Result<Option<Self::Ok>, Self::Error>;
-}
-
-impl<T> NotFound for Result<T, clap::Error> {
-    type Ok = T;
-    type Error = clap::Error;
-
-    /// Maps the Result to an Option, translating the ArgumentNotFound error to
-    /// Ok(None), while mapping other kinds of errors to Err(e).
-    ///
-    /// This allows to get proper error reporting for invalid values on optional
-    /// arguments.
-    fn or_none(self) -> Result<Option<T>, clap::Error> {
-        self.map_or_else(
-            |e| match e.kind() {
-                clap::error::ErrorKind::UnknownArgument => Ok(None),
-                _ => Err(e),
-            },
-            |v| Ok(Some(v)),
-        )
-    }
-}
-
 fn parse_background_color(s: &str) -> Result<Option<Color>, String> {
     match s {
         "none" | "None" => Ok(None),

rsvg_convert/tests/internal_predicates/svg.rs

@@ -105,10 +105,6 @@ impl cmp::PartialEq for Dimensions {
 
 impl cmp::Eq for Dimensions {}
 
-trait Details {
-    fn get_size(&self) -> Option<Dimensions>;
-}
-
 impl DetailPredicate<SvgPredicate> {
     fn eval_doc(&self, handle: &SvgHandle) -> bool {
         match &self.d {