Add a `frame` method to Explain

src/explain.rs

@@ -3,20 +3,17 @@ use std::sync::Arc;
 
 use crate::{How, IntoContext, Detail};
 
-pub trait Explain {
+pub trait Explain: Sized {
     type Output;
 
     #[track_caller]
     #[must_use]
     fn context(self, context: impl IntoContext) -> Self::Output;
-}
 
-impl Explain for How {
-    type Output = Self;
-
-    #[track_caller]
     #[inline]
-    fn context(mut self, context: impl IntoContext) -> Self {
+    #[track_caller]
+    #[must_use]
+    fn frame(self, context: impl IntoContext) -> Self::Output {
         let mut context = context.into_context();
 
         context.extra.reserve(if cfg!(feature = "extra-backtrace") {
@@ -27,7 +24,18 @@ impl Explain for How {
         context.extra.push(Detail::Location(*Location::caller()));
         #[cfg(feature = "extra-backtrace")]
         context.extra.push(Detail::backtrace());
-        self.push_context(context);
+
+        self.context(context)
+    }
+}
+
+impl Explain for How {
+    type Output = Self;
+
+    #[inline(always)]
+    #[track_caller]
+    fn context(mut self, context: impl IntoContext) -> Self {
+        self.push_context(context.into_context());
         self
     }
 }
@@ -70,20 +78,20 @@ where
 {
     type Output = How;
 
+    #[inline]
     #[track_caller]
     fn context(self, context: impl IntoContext) -> Self::Output {
-        How::new(self.into_context())
-            .context(context)
+        How::new(self).context(context)
     }
 }
 
 impl Explain for Arc<dyn std::error::Error + Send + Sync> {
     type Output = How;
 
+    #[inline]
     #[track_caller]
     fn context(self, context: impl IntoContext) -> Self::Output {
-        How::new(self.into_context())
-            .context(context)
+        How::new(self).context(context)
     }
 }
 

src/how.rs

@@ -30,7 +30,7 @@ impl How {
             location,
             context: Vec::with_capacity(4),
         }))
-        .context(context);
+        .frame(context);
         #[cfg(all(feature = "backtrace", not(feature = "extra-backtrace")))]
         how.top_mut().extra.push(Detail::backtrace());
         how