Report Windows panics through MessageBox

Alacritty is often spawned through the executable on
Windows. Since this doesn't allow access to the stderr
and crashes on startup are more common on Windows
due to the agent, it can be hard to troubleshoot issues.

This reports all Alacritty crashes through error popups
on Windows, which should resolve the problem of
crashing Alacritty instances without any error feedback.

4 files changed, 58 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7ae5f202..6d0b0c30 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - New configuration field `visual_bell.color` allows changing the visual bell color
+- Crashes on Windows are now also reported with a popup in addition to stderr
 
 ### Fixed
 
diff --git a/src/lib.rs b/src/lib.rs
index d52c457b..30eb408d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -49,6 +49,7 @@ pub mod input;
 pub mod locale;
 pub mod logging;
 pub mod meter;
+pub mod panic;
 pub mod renderer;
 pub mod selection;
 pub mod sync;
diff --git a/src/main.rs b/src/main.rs
index fea14b5f..2ce43fe1 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -47,12 +47,15 @@ use alacritty::config::{self, Config, Error as ConfigError};
 use alacritty::display::Display;
 use alacritty::event_loop::{self, EventLoop, Msg};
 use alacritty::logging::{self, LoggerProxy};
+use alacritty::panic;
 use alacritty::sync::FairMutex;
 use alacritty::term::Term;
 use alacritty::tty::{self, process_should_exit};
 use alacritty::util::fmt::Red;
 
 fn main() {
+    panic::attach_handler();
+
     // When linked with the windows subsystem windows won't automatically attach
     // to the console of the parent process, so we do it explicitly. This fails
     // silently if the parent has no console.
diff --git a/src/panic.rs b/src/panic.rs
new file mode 100644
index 00000000..4d3524ed
--- /dev/null
+++ b/src/panic.rs
@@ -0,0 +1,53 @@
+// Copyright 2016 Joe Wilm, The Alacritty Project Contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+//! ANSI Terminal Stream Parsing
+
+// Use the default behavior of the other platforms.
+#[cfg(not(windows))]
+pub fn attach_handler() {}
+
+// Install a panic handler that renders the panic in a classical Windows error
+// dialog box as well as writes the panic to STDERR.
+#[cfg(windows)]
+pub fn attach_handler() {
+    use std::{io, io::Write, panic, ptr};
+    use winapi::um::winuser;
+
+    panic::set_hook(Box::new(|panic_info| {
+        let _ = writeln!(io::stderr(), "{}", panic_info);
+        let msg = format!("{}\n\nPress Ctrl-C to Copy", panic_info);
+        unsafe {
+            winuser::MessageBoxW(
+                ptr::null_mut(),
+                win32_string(&msg).as_ptr(),
+                win32_string("Alacritty: Runtime Error").as_ptr(),
+                winuser::MB_ICONERROR
+                    | winuser::MB_OK
+                    | winuser::MB_SETFOREGROUND
+                    | winuser::MB_TASKMODAL,
+            );
+        }
+    }));
+}
+
+// Converts the string slice into a Windows-standard representation for "W"-
+// suffixed function variants, which accept UTF-16 encoded string values.
+#[cfg(windows)]
+fn win32_string(value: &str) -> Vec<u16> {
+    use std::ffi::OsStr;
+    use std::iter::once;
+    use std::os::windows::ffi::OsStrExt;
+    OsStr::new(value).encode_wide().chain(once(0)).collect()
+}