From 611701c36290b81c3c51ed30c49245f341a580e8 Mon Sep 17 00:00:00 2001
From: Michael Davis <mcarsondavis@gmail.com>
Date: Sun, 5 Mar 2023 12:13:11 -0600
Subject: [PATCH] tui: Cache the keyboard enhancement check

Wether the host terminal supports keyboard enhancement can be cached
for the lifetime of a Helix session.

Caching this lookup prevents a potential lockup within crossterm's
event reading system where the query for the keyboard enhancement
support waits on the next keyboard event, which can happen if the
crossterm event stream is checked by `tokio::select!` in another
thread.
---
 Cargo.lock                         |  1 +
 helix-tui/Cargo.toml               |  1 +
 helix-tui/src/backend/crossterm.rs | 14 ++++++++++++--
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 231273956..a03f9c921 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1202,6 +1202,7 @@ dependencies = [
  "helix-core",
  "helix-view",
  "log",
+ "once_cell",
  "serde",
  "termini",
  "unicode-segmentation",
diff --git a/helix-tui/Cargo.toml b/helix-tui/Cargo.toml
index 3ca7e044e..8a6d5367d 100644
--- a/helix-tui/Cargo.toml
+++ b/helix-tui/Cargo.toml
@@ -22,6 +22,7 @@ unicode-segmentation = "1.10"
 crossterm = { version = "0.26", optional = true }
 termini = "0.1"
 serde = { version = "1", "optional" = true, features = ["derive"]}
+once_cell = "1.17"
 log = "~0.4"
 helix-view = { version = "0.6", path = "../helix-view", features = ["term"] }
 helix-core = { version = "0.6", path = "../helix-core" }
diff --git a/helix-tui/src/backend/crossterm.rs b/helix-tui/src/backend/crossterm.rs
index e81c1e008..7c512ce3e 100644
--- a/helix-tui/src/backend/crossterm.rs
+++ b/helix-tui/src/backend/crossterm.rs
@@ -15,6 +15,7 @@
     Command,
 };
 use helix_view::graphics::{Color, CursorKind, Modifier, Rect, UnderlineStyle};
+use once_cell::sync::OnceCell;
 use std::{
     fmt,
     io::{self, Write},
@@ -57,6 +58,7 @@ pub fn from_env_or_default() -> Self {
 pub struct CrosstermBackend<W: Write> {
     buffer: W,
     capabilities: Capabilities,
+    supports_keyboard_enhancement_protocol: OnceCell<bool>,
 }
 
 impl<W> CrosstermBackend<W>
@@ -67,8 +69,16 @@ pub fn new(buffer: W) -> CrosstermBackend<W> {
         CrosstermBackend {
             buffer,
             capabilities: Capabilities::from_env_or_default(),
+            supports_keyboard_enhancement_protocol: OnceCell::new(),
         }
     }
+
+    #[inline]
+    fn supports_keyboard_enhancement_protocol(&self) -> io::Result<bool> {
+        self.supports_keyboard_enhancement_protocol
+            .get_or_try_init(terminal::supports_keyboard_enhancement)
+            .copied()
+    }
 }
 
 impl<W> Write for CrosstermBackend<W>
@@ -100,7 +110,7 @@ fn claim(&mut self, config: Config) -> io::Result<()> {
         if config.enable_mouse_capture {
             execute!(self.buffer, EnableMouseCapture)?;
         }
-        if matches!(terminal::supports_keyboard_enhancement(), Ok(true)) {
+        if self.supports_keyboard_enhancement_protocol()? {
             log::debug!("The enhanced keyboard protocol is supported on this terminal");
             execute!(
                 self.buffer,
@@ -121,7 +131,7 @@ fn restore(&mut self, config: Config) -> io::Result<()> {
         if config.enable_mouse_capture {
             execute!(self.buffer, DisableMouseCapture)?;
         }
-        if matches!(terminal::supports_keyboard_enhancement(), Ok(true)) {
+        if self.supports_keyboard_enhancement_protocol()? {
             execute!(self.buffer, PopKeyboardEnhancementFlags)?;
         }
         execute!(