Move terminal claim/restore code to helix-tui

This moves the `Application::claim_term` and
`helix-term::application::restore_term` functions into the helix-tui
crate. How the terminal should be claimed and restored is a TUI concern
and is implemented differently through different TUI backends.

This cleans out a lot of crossterm and TUI code in Application and
makes it easier to modify claim/restore based on information we query
from the terminal host. The child commit will take advantage of this
to cache the check for whether the host terminal supports the keyboard
enhancement protocol. Without this change, caching that information
takes much more code which is not easily reusable for anything else.

The code to restore the terminal is somewhat duplicated by this patch:
we want to restore the terminal in cases of panics. Panic handler hooks
must live for `'static` and the Application's terminal does not.

1 files changed, 69 insertions, 1 deletions

diff --git a/helix-tui/src/backend/crossterm.rs b/helix-tui/src/backend/crossterm.rs
index 5305640c..e81c1e00 100644
--- a/helix-tui/src/backend/crossterm.rs
+++ b/helix-tui/src/backend/crossterm.rs
@@ -1,6 +1,11 @@
-use crate::{backend::Backend, buffer::Cell};
+use crate::{backend::Backend, buffer::Cell, terminal::Config};
 use crossterm::{
     cursor::{Hide, MoveTo, SetCursorStyle, Show},
+    event::{
+        DisableBracketedPaste, DisableFocusChange, DisableMouseCapture, EnableBracketedPaste,
+        EnableFocusChange, EnableMouseCapture, KeyboardEnhancementFlags,
+        PopKeyboardEnhancementFlags, PushKeyboardEnhancementFlags,
+    },
     execute, queue,
     style::{
         Attribute as CAttribute, Color as CColor, Print, SetAttribute, SetBackgroundColor,
@@ -83,6 +88,69 @@ impl<W> Backend for CrosstermBackend<W>
 where
     W: Write,
 {
+    fn claim(&mut self, config: Config) -> io::Result<()> {
+        terminal::enable_raw_mode()?;
+        execute!(
+            self.buffer,
+            terminal::EnterAlternateScreen,
+            EnableBracketedPaste,
+            EnableFocusChange
+        )?;
+        execute!(self.buffer, terminal::Clear(terminal::ClearType::All))?;
+        if config.enable_mouse_capture {
+            execute!(self.buffer, EnableMouseCapture)?;
+        }
+        if matches!(terminal::supports_keyboard_enhancement(), Ok(true)) {
+            log::debug!("The enhanced keyboard protocol is supported on this terminal");
+            execute!(
+                self.buffer,
+                PushKeyboardEnhancementFlags(
+                    KeyboardEnhancementFlags::DISAMBIGUATE_ESCAPE_CODES
+                        | KeyboardEnhancementFlags::REPORT_ALTERNATE_KEYS
+                )
+            )?;
+        } else {
+            log::debug!("The enhanced keyboard protocol is not supported on this terminal");
+        }
+        Ok(())
+    }
+
+    fn restore(&mut self, config: Config) -> io::Result<()> {
+        // reset cursor shape
+        write!(self.buffer, "\x1B[0 q")?;
+        if config.enable_mouse_capture {
+            execute!(self.buffer, DisableMouseCapture)?;
+        }
+        if matches!(terminal::supports_keyboard_enhancement(), Ok(true)) {
+            execute!(self.buffer, PopKeyboardEnhancementFlags)?;
+        }
+        execute!(
+            self.buffer,
+            DisableBracketedPaste,
+            DisableFocusChange,
+            terminal::LeaveAlternateScreen
+        )?;
+        terminal::disable_raw_mode()
+    }
+
+    fn force_restore() -> io::Result<()> {
+        let mut stdout = io::stdout();
+
+        // reset cursor shape
+        write!(stdout, "\x1B[0 q")?;
+        // 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,
+            DisableFocusChange,
+            terminal::LeaveAlternateScreen
+        )?;
+        terminal::disable_raw_mode()
+    }
+
     fn draw<'a, I>(&mut self, content: I) -> io::Result<()>
     where
         I: Iterator<Item = (u16, u16, &'a Cell)>,