From a8649ac5f282aea8798256162eedaae24cf71b65 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Thu, 20 Oct 2022 15:17:32 -0700
Subject: [PATCH] Remove 2 frames of backtrace noise on Option's Context impl

Repro:

    use anyhow::Context;

    fn main() -> anyhow::Result<()> {
        let result = None::<()>;
        result.context("...")
    }

Before:

    0: anyhow::context::<impl anyhow::Context<T,core::convert::Infallible> for core::option::Option<T>>::context::{{closure}}
              at /git/anyhow/src/context.rs:95:57
    1: core::option::Option<T>::ok_or_else
              at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/core/src/option.rs:1083:25
    2: anyhow::context::<impl anyhow::Context<T,core::convert::Infallible> for core::option::Option<T>>::context
              at /git/anyhow/src/context.rs:95:9
    3: testing::main
              at ./src/main.rs:5:5

After:

    0: anyhow::context::<impl anyhow::Context<T,core::convert::Infallible> for core::option::Option<T>>::context
              at /git/anyhow/src/context.rs:99:54
    1: testing::main
              at ./src/main.rs:5:5
---
 src/context.rs | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/context.rs b/src/context.rs
index 238473e..c8bd4f0 100644
--- a/src/context.rs
+++ b/src/context.rs
@@ -92,7 +92,12 @@ impl<T> Context<T, Infallible> for Option<T> {
     where
         C: Display + Send + Sync + 'static,
     {
-        self.ok_or_else(|| Error::from_display(context, backtrace!()))
+        // Not using ok_or_else to save 2 useless frames off the captured
+        // backtrace.
+        match self {
+            Some(ok) => Ok(ok),
+            None => Err(Error::from_display(context, backtrace!())),
+        }
     }
 
     fn with_context<C, F>(self, context: F) -> Result<T, Error>
@@ -100,7 +105,10 @@ impl<T> Context<T, Infallible> for Option<T> {
         C: Display + Send + Sync + 'static,
         F: FnOnce() -> C,
     {
-        self.ok_or_else(|| Error::from_display(context(), backtrace!()))
+        match self {
+            Some(ok) => Ok(ok),
+            None => Err(Error::from_display(context(), backtrace!())),
+        }
     }
 }