Add doc for impl From for Std Error

src/libstd/error.rs

@@ -152,20 +152,24 @@ pub trait Error: Debug + Display {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
+    /// Converts a type of [`Error`] into a box of dyn [`Error`].
     fn from(err: E) -> Box<dyn Error + 'a> {
         Box::new(err)
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
+    /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of dyn [`Error`] +
+    /// [`Send`] + [`Sync`].
     fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
         Box::new(err)
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl From<String> for Box<dyn Error + Send + Sync> {
+    /// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
     fn from(err: String) -> Box<dyn Error + Send + Sync> {
         #[derive(Debug)]
         struct StringError(String);
@@ -186,6 +190,7 @@ impl From<String> for Box<dyn Error + Send + Sync> {
 
 #[stable(feature = "string_box_error", since = "1.6.0")]
 impl From<String> for Box<dyn Error> {
+    /// Converts a [`String`] into a box of dyn [`Error`].
     fn from(str_err: String) -> Box<dyn Error> {
         let err1: Box<dyn Error + Send + Sync> = From::from(str_err);
         let err2: Box<dyn Error> = err1;
@@ -195,27 +200,31 @@ impl From<String> for Box<dyn Error> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, 'b> From<&'b str> for Box<dyn Error + Send + Sync + 'a> {
+    /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
     fn from(err: &'b str) -> Box<dyn Error + Send + Sync + 'a> {
         From::from(String::from(err))
     }
 }
 
 #[stable(feature = "string_box_error", since = "1.6.0")]
 impl<'a> From<&'a str> for Box<dyn Error> {
+    /// Converts a [`str`] into a box of dyn [`Error`].
     fn from(err: &'a str) -> Box<dyn Error> {
         From::from(String::from(err))
     }
 }
 
 #[stable(feature = "cow_box_error", since = "1.22.0")]
 impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
+    /// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
     fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> {
         From::from(String::from(err))
     }
 }
 
 #[stable(feature = "cow_box_error", since = "1.22.0")]
 impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
+    /// Converts a [`Cow`] into a box of dyn [`Error`].
     fn from(err: Cow<'a, str>) -> Box<dyn Error> {
         From::from(String::from(err))
     }