feat: add annotate() method to Context

to just annotate the passed error with location data

Signed-off-by: Harald Hoyer <harald@hoyer.xyz>

examples/example.rs

@@ -1,4 +1,4 @@
-use chainerror::prelude::v2::*;
+use chainerror::Context as _;
 use std::error::Error;
 use std::fmt;
 use std::io;
@@ -8,12 +8,17 @@ fn do_some_io() -> Result<(), Box<dyn Error + Send + Sync>> {
     Ok(())
 }
 
-fn func3() -> Result<(), Box<dyn Error + Send + Sync>> {
+fn func4() -> Result<(), Box<dyn Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().context(format!("Error reading '{}'", filename))?;
     Ok(())
 }
 
+fn func3() -> Result<(), Box<dyn Error + Send + Sync>> {
+    func4().annotate()?;
+    Ok(())
+}
+
 chainerror::str_context!(Func2Error);
 
 fn func2() -> chainerror::Result<(), Func2Error> {

src/lib.rs

@@ -216,6 +216,9 @@ pub trait Context<O, E: Into<Box<dyn StdError + 'static + Send + Sync>>> {
     /// Decorate the error with a `kind` of type `T` and the source `Location`
     fn context<T: 'static + Display + Debug>(self, kind: T) -> std::result::Result<O, Error<T>>;
 
+    /// Decorate the error just with the source `Location`
+    fn annotate(self) -> std::result::Result<O, Error<AnnotatedError>>;
+
     /// Decorate the `error` with a `kind` of type `T` produced with a `FnOnce(&error)` and the source `Location`
     fn map_context<T: 'static + Display + Debug, F: FnOnce(&E) -> T>(
         self,
@@ -223,6 +226,21 @@ pub trait Context<O, E: Into<Box<dyn StdError + 'static + Send + Sync>>> {
     ) -> std::result::Result<O, Error<T>>;
 }
 
+/// Convenience type to just decorate the error with the source `Location`
+pub struct AnnotatedError(());
+
+impl Display for AnnotatedError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "(passed error)")
+    }
+}
+
+impl Debug for AnnotatedError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "(passed error)")
+    }
+}
+
 impl<O, E: Into<Box<dyn StdError + 'static + Send + Sync>>> Context<O, E>
     for std::result::Result<O, E>
 {
@@ -239,6 +257,19 @@ impl<O, E: Into<Box<dyn StdError + 'static + Send + Sync>>> Context<O, E>
         }
     }
 
+    #[track_caller]
+    #[inline]
+    fn annotate(self) -> std::result::Result<O, Error<AnnotatedError>> {
+        match self {
+            Ok(t) => Ok(t),
+            Err(error_cause) => Err(Error::new(
+                AnnotatedError(()),
+                Some(error_cause.into()),
+                Some(Location::caller().to_string()),
+            )),
+        }
+    }
+
     #[track_caller]
     #[inline]
     fn map_context<T: 'static + Display + Debug, F: FnOnce(&E) -> T>(