tui: Only query keyboard enhancement support once

helix-term/src/application.rs

@@ -112,12 +112,10 @@ fn restore_term() -> Result<(), Error> {
     let mut stdout = stdout();
     // reset cursor shape
     write!(stdout, "\x1B[0 q")?;
-    if matches!(terminal::supports_keyboard_enhancement(), Ok(true)) {
-        execute!(stdout, PopKeyboardEnhancementFlags)?;
-    }
     // Ignore errors on disabling, this might trigger on windows if we call
     // disable without calling enable previously
     let _ = execute!(stdout, DisableMouseCapture);
+    let _ = execute!(stdout, PopKeyboardEnhancementFlags);
     execute!(
         stdout,
         DisableBracketedPaste,
@@ -1071,7 +1069,10 @@ impl Application {
         if self.config.load().editor.mouse {
             execute!(stdout, EnableMouseCapture)?;
         }
-        if matches!(terminal::supports_keyboard_enhancement(), Ok(true)) {
+        if matches!(
+            self.terminal.supports_keyboard_enhancement_protocol(),
+            Ok(true)
+        ) {
             log::debug!("The enhanced keyboard protocol is supported on this terminal");
             execute!(
                 stdout,

helix-tui/Cargo.toml

@@ -22,5 +22,6 @@ unicode-segmentation = "1.10"
 crossterm = { version = "0.26", optional = true }
 termini = "0.1"
 serde = { version = "1", "optional" = true, features = ["derive"]}
+once_cell = "1.17"
 helix-view = { version = "0.6", path = "../helix-view", features = ["term"] }
 helix-core = { version = "0.6", path = "../helix-core" }

helix-tui/src/backend/crossterm.rs

@@ -10,6 +10,7 @@ use crossterm::{
     Command,
 };
 use helix_view::graphics::{Color, CursorKind, Modifier, Rect, UnderlineStyle};
+use once_cell::sync::OnceCell;
 use std::{
     fmt,
     io::{self, Write},
@@ -52,6 +53,7 @@ impl Capabilities {
 pub struct CrosstermBackend<W: Write> {
     buffer: W,
     capabilities: Capabilities,
+    supports_keyboard_enhancement_protocol: OnceCell<bool>,
 }
 
 impl<W> CrosstermBackend<W>
@@ -62,6 +64,7 @@ where
         CrosstermBackend {
             buffer,
             capabilities: Capabilities::from_env_or_default(),
+            supports_keyboard_enhancement_protocol: OnceCell::new(),
         }
     }
 }
@@ -187,6 +190,12 @@ where
     fn flush(&mut self) -> io::Result<()> {
         self.buffer.flush()
     }
+
+    fn supports_keyboard_enhancement_protocol(&self) -> Result<bool, io::Error> {
+        self.supports_keyboard_enhancement_protocol
+            .get_or_try_init(terminal::supports_keyboard_enhancement)
+            .copied()
+    }
 }
 
 fn map_error(error: crossterm::Result<()>) -> io::Result<()> {

helix-tui/src/backend/mod.rs

@@ -23,4 +23,5 @@ pub trait Backend {
     fn clear(&mut self) -> Result<(), io::Error>;
     fn size(&self) -> Result<Rect, io::Error>;
     fn flush(&mut self) -> Result<(), io::Error>;
+    fn supports_keyboard_enhancement_protocol(&self) -> Result<bool, io::Error>;
 }

helix-tui/src/backend/test.rs

@@ -147,4 +147,8 @@ impl Backend for TestBackend {
     fn flush(&mut self) -> Result<(), io::Error> {
         Ok(())
     }
+
+    fn supports_keyboard_enhancement_protocol(&self) -> Result<bool, io::Error> {
+        Ok(false)
+    }
 }

helix-tui/src/terminal.rs

@@ -222,4 +222,10 @@ where
     pub fn size(&self) -> io::Result<Rect> {
         self.backend.size()
     }
+
+    /// Checks whether the host terminal emulator supports the keyboard
+    /// enhancement protocol for disambiguating keycodes.
+    pub fn supports_keyboard_enhancement_protocol(&self) -> io::Result<bool> {
+        self.backend.supports_keyboard_enhancement_protocol()
+    }
 }