Mark error construction as cold code

src/error.rs

@@ -264,6 +264,7 @@ pub enum ErrorCode {
 impl Error {
     // Not public API. Should be pub(crate).
     #[doc(hidden)]
+    #[cold]
     pub fn syntax(code: ErrorCode, line: usize, column: usize) -> Self {
         Error {
             err: Box::new(ErrorImpl {
@@ -278,6 +279,7 @@ impl Error {
     //
     // Update `eager_json` crate when this function changes.
     #[doc(hidden)]
+    #[cold]
     pub fn io(error: io::Error) -> Self {
         Error {
             err: Box::new(ErrorImpl {
@@ -290,6 +292,7 @@ impl Error {
 
     // Not public API. Should be pub(crate).
     #[doc(hidden)]
+    #[cold]
     pub fn fix_position<F>(self, f: F) -> Self
     where
         F: FnOnce(ErrorCode) -> Error,
@@ -391,6 +394,7 @@ impl Debug for Error {
 }
 
 impl de::Error for Error {
+    #[cold]
     fn custom<T: Display>(msg: T) -> Error {
         Error {
             err: Box::new(ErrorImpl {
@@ -401,6 +405,7 @@ impl de::Error for Error {
         }
     }
 
+    #[cold]
     fn invalid_type(unexp: de::Unexpected, exp: &de::Expected) -> Self {
         if let de::Unexpected::Unit = unexp {
             Error::custom(format_args!("invalid type: null, expected {}", exp))
@@ -411,6 +416,7 @@ impl de::Error for Error {
 }
 
 impl ser::Error for Error {
+    #[cold]
     fn custom<T: Display>(msg: T) -> Error {
         Error {
             err: Box::new(ErrorImpl {

src/number.rs

@@ -748,6 +748,7 @@ impl Number {
     #[cfg(not(feature = "arbitrary_precision"))]
     // Not public API. Should be pub(crate).
     #[doc(hidden)]
+    #[cold]
     pub fn unexpected(&self) -> Unexpected {
         match self.n {
             N::PosInt(u) => Unexpected::Unsigned(u),
@@ -759,6 +760,7 @@ impl Number {
     #[cfg(feature = "arbitrary_precision")]
     // Not public API. Should be pub(crate).
     #[doc(hidden)]
+    #[cold]
     pub fn unexpected(&self) -> Unexpected {
         Unexpected::Other("number")
     }

src/value/de.rs

@@ -1409,6 +1409,7 @@ impl Value {
         serde::de::Error::invalid_type(self.unexpected(), exp)
     }
 
+    #[cold]
     fn unexpected(&self) -> Unexpected {
         match *self {
             Value::Null => Unexpected::Unit,