Rollup merge of rust-lang#39960 - lukaramu:issue-39925, r=alexcrichton

added Error and Display impl for std::ffi::FromBytesWithNulError

Fixes rust-lang#39925.

This is my first PR, so I wasn't quite sure about the stability annotation.

src/libstd/ffi/c_str.rs

@@ -455,6 +455,20 @@ impl From<NulError> for io::Error {
  }
 }
 
+#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
+impl Error for FromBytesWithNulError {
+ fn description(&self) -> &str {
+ "data provided is not null terminated or contains an interior nul byte"
+ }
+}
+
+#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
+impl fmt::Display for FromBytesWithNulError {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ self.description().fmt(f)
+ }
+}
+
 impl IntoStringError {
  /// Consumes this error, returning original `CString` which generated the
  /// error.