verbose errors feature

src/fs/file.rs

@@ -9,6 +9,7 @@ use std::sync::{Arc, Mutex};
 
 use crate::fs::{Metadata, Permissions};
 use crate::future;
+use crate::utils::Context as _;
 use crate::io::{self, Read, Seek, SeekFrom, Write};
 use crate::path::Path;
 use crate::prelude::*;
@@ -112,7 +113,11 @@ impl File {
     /// ```
     pub async fn open<P: AsRef<Path>>(path: P) -> io::Result<File> {
         let path = path.as_ref().to_owned();
-        let file = spawn_blocking(move || std::fs::File::open(&path)).await?;
+        let file = spawn_blocking(move || {
+            std::fs::File::open(&path)
+                .context(|| format!("Could not open {}", path.display()))
+        })
+        .await?;
         Ok(File::new(file, true))
     }
 
@@ -147,7 +152,11 @@ impl File {
     /// ```
     pub async fn create<P: AsRef<Path>>(path: P) -> io::Result<File> {
         let path = path.as_ref().to_owned();
-        let file = spawn_blocking(move || std::fs::File::create(&path)).await?;
+        let file = spawn_blocking(move || {
+            std::fs::File::create(&path)
+                .context(|| format!("Could not create {}", path.display()))
+        })
+        .await?;
         Ok(File::new(file, true))
     }
 

src/io/mod.rs

@@ -291,6 +291,7 @@ cfg_std! {
     pub(crate) mod read;
     pub(crate) mod seek;
     pub(crate) mod write;
+    pub(crate) mod utils;
 
     mod buf_reader;
     mod buf_writer;

src/io/utils.rs

@@ -0,0 +1,46 @@
+use crate::utils::Context;
+
+/// Wrap `std::io::Error` with additional message
+///
+/// Keeps the original error kind and stores the original I/O error as `source`.
+impl<T> Context for Result<T, std::io::Error> {
+    fn context(self, message: impl Fn() -> String) -> Self {
+        self.map_err(|e| VerboseError::wrap(e, message()))
+    }
+}
+
+use std::{error::Error as StdError, fmt, io};
+
+#[derive(Debug)]
+pub(crate) struct VerboseError {
+    source: io::Error,
+    message: String,
+}
+
+impl VerboseError {
+    pub(crate) fn wrap(source: io::Error, message: impl Into<String>) -> io::Error {
+        io::Error::new(
+            source.kind(),
+            VerboseError {
+                source,
+                message: message.into(),
+            },
+        )
+    }
+}
+
+impl fmt::Display for VerboseError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.message)
+    }
+}
+
+impl StdError for VerboseError {
+    fn description(&self) -> &str {
+        self.source.description()
+    }
+
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        Some(&self.source)
+    }
+}

src/utils.rs

@@ -52,6 +52,11 @@ pub fn random(n: u32) -> u32 {
     })
 }
 
+/// Add additional context to errors
+pub(crate) trait Context {
+    fn context(self, message: impl Fn() -> String) -> Self;
+}
+
 /// Defers evaluation of a block of code until the end of the scope.
 #[cfg(feature = "default")]
 #[doc(hidden)]

tests/verbose_errors.rs

@@ -0,0 +1,16 @@
+use async_std::{fs, task};
+
+#[test]
+fn open_file() {
+    task::block_on(async {
+        let non_existing_file = "/ashjudlkahasdasdsikdhajik/asdasdasdasdasdasd/fjuiklashdbflasas";
+        let res = fs::File::open(non_existing_file).await;
+        match res {
+            Ok(_) => panic!("Found file with random name: We live in a simulation"),
+            Err(e) => assert_eq!(
+                "Could not open /ashjudlkahasdasdsikdhajik/asdasdasdasdasdasd/fjuiklashdbflasas",
+                &format!("{}", e)
+            ),
+        }
+    })
+}