From d3a2b21a8c34c7b7eea0a001a1412992e3ed2cb7 Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Tue, 29 Sep 2020 20:08:27 +0200
Subject: Add panic_context module for better panic messages

---
 crates/rust-analyzer/src/dispatch.rs |  7 ++++--
 crates/stdx/src/lib.rs               |  1 +
 crates/stdx/src/panic_context.rs     | 49 ++++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 crates/stdx/src/panic_context.rs

diff --git a/crates/rust-analyzer/src/dispatch.rs b/crates/rust-analyzer/src/dispatch.rs
index 891fdb96d..36f0c1d52 100644
--- a/crates/rust-analyzer/src/dispatch.rs
+++ b/crates/rust-analyzer/src/dispatch.rs
@@ -1,5 +1,5 @@
 //! A visitor for downcasting arbitrary request (JSON) into a specific type.
-use std::panic;
+use std::{fmt, panic};
 
 use serde::{de::DeserializeOwned, Serialize};
 
@@ -49,7 +49,7 @@ impl<'a> RequestDispatcher<'a> {
     ) -> Result<&mut Self>
     where
         R: lsp_types::request::Request + 'static,
-        R::Params: DeserializeOwned + Send + 'static,
+        R::Params: DeserializeOwned + Send + fmt::Debug + 'static,
         R::Result: Serialize + 'static,
     {
         let (id, params) = match self.parse::<R>() {
@@ -61,7 +61,10 @@ impl<'a> RequestDispatcher<'a> {
 
         self.global_state.task_pool.handle.spawn({
             let world = self.global_state.snapshot();
+
             move || {
+                let _ctx =
+                    stdx::panic_context::enter(format!("request: {} {:#?}", R::METHOD, params));
                 let result = f(world, params);
                 Task::Response(result_to_response::<R>(id, result))
             }
diff --git a/crates/stdx/src/lib.rs b/crates/stdx/src/lib.rs
index 273b0f55b..011935cad 100644
--- a/crates/stdx/src/lib.rs
+++ b/crates/stdx/src/lib.rs
@@ -5,6 +5,7 @@ use std::{
 };
 
 mod macros;
+pub mod panic_context;
 
 #[inline(always)]
 pub fn is_ci() -> bool {
diff --git a/crates/stdx/src/panic_context.rs b/crates/stdx/src/panic_context.rs
new file mode 100644
index 000000000..fd232e0cc
--- /dev/null
+++ b/crates/stdx/src/panic_context.rs
@@ -0,0 +1,49 @@
+//! A micro-crate to enhance panic messages with context info.
+//!
+//! FIXME: upstream to https://github.com/kriomant/panic-context ?
+
+use std::{cell::RefCell, panic, sync::Once};
+
+pub fn enter(context: String) -> impl Drop {
+    static ONCE: Once = Once::new();
+    ONCE.call_once(PanicContext::init);
+
+    with_ctx(|ctx| ctx.push(context));
+    PanicContext { _priv: () }
+}
+
+#[must_use]
+struct PanicContext {
+    _priv: (),
+}
+
+impl PanicContext {
+    fn init() {
+        let default_hook = panic::take_hook();
+        let hook = move |panic_info: &panic::PanicInfo<'_>| {
+            with_ctx(|ctx| {
+                if !ctx.is_empty() {
+                    eprintln!("Panic context:");
+                    for frame in ctx.iter() {
+                        eprintln!("> {}\n", frame)
+                    }
+                }
+                default_hook(panic_info)
+            })
+        };
+        panic::set_hook(Box::new(hook))
+    }
+}
+
+impl Drop for PanicContext {
+    fn drop(&mut self) {
+        with_ctx(|ctx| assert!(ctx.pop().is_some()))
+    }
+}
+
+fn with_ctx(f: impl FnOnce(&mut Vec<String>)) {
+    thread_local! {
+        static CTX: RefCell<Vec<String>> = RefCell::new(Vec::new());
+    }
+    CTX.with(|ctx| f(&mut *ctx.borrow_mut()))
+}
-- 
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