Added `err` module: Wrapped OS errors; Ad-hoc inline definitions, and named definitions with pre-defined messages.

Fortune for mapped-file's current commit: Future small blessing − 末小吉

Cargo.toml

@@ -1,6 +1,7 @@
 [package]
 name = "mapped-file"
-description = "construct a memory mapping over any file object"
+description = "Construct a memory mapping over any file object"
+keywords = ["unix", "mmap", "generic", "file", "fd"]
 version = "0.1.0"
 edition = "2021"
 

src/err.rs

@@ -0,0 +1,170 @@
+//! Wrapping `errno` error types
+use super::*;
+use std::ffi::c_int;
+use std::{
+    fmt, error
+};
+
+/// Construct an ad-hoc error wrapping the last OS error.
+macro_rules! os_error {
+    ($fmt:literal $(, $args:expr)*) => {
+	{
+	    #[derive(Debug)]
+            struct AdHoc<'a>(::std::fmt::Arguments<'a>);
+	    impl<'a> ::std::fmt::Display for AdHoc<'a>
+	    {
+		#[inline] 
+		fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+		{
+		    write!(f, "{}", self.0)
+		}
+	    }
+	    $crate::err::WrappedOSError::last_os_error(AdHoc(::std::format_args!($fmt $(, $args)*)))
+	}
+    };
+    ($(#[$outer:meta])* $vis:vis struct $name:ident => $fmt:literal $(; $($rest:tt)*)?) => {
+
+	$(#[$outer])*
+	    #[derive(Debug)]
+	#[repr(transparent)]
+	$vis struct $name($crate::err::WrappedOSError<&'static str>);
+
+	impl ::std::fmt::Display for $name
+	{
+	    #[inline] 
+	    fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> fmt::Result
+	    {
+		f.write_str($fmt)
+	    }
+	}
+	impl ::std::error::Error for $name {
+	    #[inline] 
+	    fn source(&self) -> Option<&(dyn ::std::error::Error + 'static)>
+	    {
+		self.0.source()
+	    }
+	}
+
+	#[allow(unused)]
+	impl $name {
+	    #[inline(always)] 
+	    fn new() -> Self
+	    {
+		Self($crate::err::WrappedOSError::last_os_error($fmt))
+	    }
+	    #[inline(always)] 
+	    fn into_inner(self) -> $crate::err::WrappedOSError<&'static str>
+	    {
+		self.0
+	    }
+	}
+	impl ::std::ops::Deref for $name {
+	    type Target = $crate::err::WrappedOSError<&'static str>;
+	    #[inline] 
+	    fn deref(&self) -> &Self::Target
+	    {
+		&self.0
+	    }
+	}
+	impl ::std::ops::DerefMut for $name {
+	    #[inline] 
+	    fn deref_mut(&mut self) -> &mut Self::Target
+	    {
+		&mut self.0
+	    }
+	}
+
+	$(
+	    $crate::os_error! {
+		$($rest)*
+	    }
+	)?
+    };
+    () => {};
+}
+pub(crate) use os_error;
+
+const _: () = {
+    os_error!(struct Test => "Test error");
+    const fn t<E: ?Sized + error::Error>() {}
+    fn r<E: ?Sized + error::Error>(_: &E) {}
+    fn test() {
+	r(&os_error!("Some error message"));
+    }
+    t::<Test>()
+};
+
+/// Wraps a piece of context over an OS error
+pub struct WrappedOSError<E: ?Sized>(io::Error, E);
+
+impl<E: fmt::Debug> WrappedOSError<E>
+{
+    pub(crate) fn last_os_error(ctx: E) -> Self
+    {
+	Self(io::Error::last_os_error(), ctx)
+    }
+
+    pub(crate) fn from_os_error(raw: c_int, ctx: E) -> Self
+    {
+	Self(io::Error::from_raw_os_error(raw), ctx)
+    }
+}
+
+impl<E: ?Sized> WrappedOSError<E>
+{
+    #[inline] 
+    pub fn error(&self) -> &io::Error
+    {
+	&self.0
+    }
+    #[inline] 
+    pub fn raw_error(&self) -> c_int
+    {
+	self.0.raw_os_error().unwrap()
+    }
+    #[inline] 
+    pub fn context(&self) -> &E
+    {
+	&self.1
+    }
+}
+
+impl<E> From<WrappedOSError<E>> for io::Error
+{
+    #[inline] 
+    fn from(from: WrappedOSError<E>) -> Self
+    {
+	from.0
+    }
+}
+
+
+impl<E: ?Sized> error::Error for WrappedOSError<E>
+where WrappedOSError<E>: fmt::Display + fmt::Debug
+{
+    #[inline] 
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+	Some(&self.0)
+    }
+}
+
+impl<E: ?Sized> fmt::Display for WrappedOSError<E>
+where E: fmt::Debug
+{
+    #[inline] 
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "{:?}", &self.1)
+    }
+}
+impl<E: ?Sized> fmt::Debug for WrappedOSError<E>
+where E: fmt::Display
+{
+    #[inline] 
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "{}", &self.1)
+    }
+}
+
+

src/ffi.rs

@@ -75,7 +75,7 @@ pub(crate) use c_try;
 /// Error context for a failed C call.
 /// Returns the invalid return value, the `errno` error, and a message.
 #[derive(Debug)]
-pub(crate) struct FFIError<'a, T>(T, io::Error, fmt::Arguments<'a>);
+pub struct FFIError<'a, T>(T, io::Error, fmt::Arguments<'a>);
 
 impl<'a, T> FFIError<'a, T>
 where FFIError<'a, T>: error::Error

src/lib.rs

@@ -14,7 +14,7 @@ use std::{
     },
     io,
     fmt, error,
-
+    
     borrow::{
 	Borrow, BorrowMut,
     }
@@ -31,6 +31,10 @@ use uniq::UniqueSlice;
 mod flags;
 pub use flags::*;
 
+pub mod err;
+use err::os_error;
+
+
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[repr(transparent)]
 struct MappedSlice(UniqueSlice<u8>);
@@ -283,7 +287,7 @@ impl<T> MappedFile<T> {
     }
 }
 
-/// Contains an OS error and a value.
+/// Error returned when mapping operation fails
 pub struct TryNewError<T: ?Sized>
 {
     error: Box<io::Error>,