Support nested details, add with_backtrace method to IntoContext, impl IntoContext for Detail

examples/output.rs

@@ -4,7 +4,8 @@ fn main0() -> Result<()> {
     Err(How::new(
         "The engine broke down"
             .with("Remember: you aren't good with cars")
-            .with("Suggestion: call a tow truck"),
+            .with("Suggestion: call a tow truck")
+            .with("Foo".with("Bar").with("Baz")),
     )
     .context(
         "While driving down a road"

src/context.rs

@@ -69,6 +69,7 @@ pub enum Detail {
     #[cfg(feature = "backtrace")]
     Backtrace(PrivateBacktrace),
     Error(PrivateError),
+    Context(Box<Context>),
 }
 
 impl Detail {
@@ -137,6 +138,7 @@ impl fmt::Display for Detail {
                 write!(f, "{}", bt)
             },
             Self::Error(PrivateError(e)) => e.fmt(f),
+            Self::Context(c) => c.fmt(f),
         }
     }
 }
@@ -154,6 +156,15 @@ pub trait IntoContext: Sized {
     fn with_caller(self) -> Context {
         self.with(Location::caller())
     }
+
+    #[inline(always)]
+    #[track_caller]
+    fn with_backtrace(self) -> Context {
+        #[cfg(feature = "backtrace")]
+        return self.with(Detail::backtrace());
+        #[cfg(not(feature = "backtrace"))]
+        self.into_context()
+    }
 }
 
 impl IntoContext for Context {
@@ -166,10 +177,12 @@ impl IntoContext for Context {
     #[track_caller]
     #[inline]
     fn with(mut self, other: impl IntoContext) -> Self {
-        let mut other = other.into_context();
-        self.extra.reserve(1 + other.extra.len());
-        self.extra.push(other.detail);
-        self.extra.append(&mut other.extra);
+        let other = other.into_context();
+        if other.extra.is_empty() {
+            self.extra.push(other.detail);
+        } else {
+            self.extra.push(Detail::Context(other.into()));
+        }
         self
     }
 }
@@ -177,14 +190,14 @@ impl IntoContext for Context {
 impl IntoContext for String {
     #[inline(always)]
     fn into_context(self) -> Context {
-        Context::new(Detail::String(self))
+        Detail::String(self).into_context()
     }
 }
 
 impl IntoContext for &'static str {
     #[inline(always)]
     fn into_context(self) -> Context {
-        Context::new(Detail::Str(self))
+        Detail::Str(self).into_context()
     }
 }
 
@@ -208,7 +221,7 @@ impl<'a> IntoContext for &'a Location<'static> {
 impl IntoContext for Location<'static> {
     #[inline]
     fn into_context(self) -> Context {
-        Context::new(Detail::Location(self))
+        Detail::Location(self).into_context()
     }
 }
 
@@ -218,14 +231,21 @@ where
 {
     #[inline]
     fn into_context(self) -> Context {
-        Context::new(Detail::Error(PrivateError(self)))
+        Detail::Error(PrivateError(self)).into_context()
     }
 }
 
 impl IntoContext for Arc<dyn std::error::Error + Send + Sync> {
     #[inline]
     fn into_context(self) -> Context {
-        Context::new(Detail::Error(PrivateError(self)))
+        Detail::Error(PrivateError(self)).into_context()
+    }
+}
+
+impl IntoContext for Detail {
+    #[inline(always)]
+    fn into_context(self) -> Context {
+        Context::new(self)
     }
 }