terminal: Clear shell after activating (#39798)

Jakub Konka created 3 weeks ago

Two tweaks were required to ensure we correctly clear the shell after
running an activate script(s):
1. PowerShell upon receiving `\r\n` input, will enter the continuation
mode (>>). To avoid this, we send an "enter" key press instead `\x0d`.
2. In order to clear the terminal _after_ issuing all activation
commands, we need to take into account the asynchronous nature of the
activation process:
   - We write the command to run the script to PTY
- We send "enter" (It is now being processed by the shell) At this point
we need to wait for the shell to finish executing before we clear the
terminal. Otherwise we will create a race where we might clear the
terminal _before_ the shell finished executing the activation script(s).
   - Write `clear`/`cls` command to PTY
- Send "enter" This way we guarantee that we clear the terminal _after_
all scripts were executed.

Closes #38474 

Release Notes:

- N/A

Change summary

crates/terminal/src/terminal.rs | 31 +++++++++++++++++++++----------
crates/util/src/shell.rs        |  7 +++++++
2 files changed, 28 insertions(+), 10 deletions(-)

Detailed changes

crates/terminal/src/terminal.rs

@@ -495,6 +495,8 @@ impl TerminalBuilder {
                 .unwrap_or(params.program.clone())
         });
 
+        let shell_kind = shell.shell_kind();
+
         let pty_options = {
             let alac_shell = shell_params.as_ref().map(|params| {
                 alacritty_terminal::tty::Shell::new(
@@ -511,7 +513,7 @@ impl TerminalBuilder {
                 // We do not want to escape arguments if we are using CMD as our shell.
                 // If we do we end up with too many quotes/escaped quotes for CMD to handle.
                 #[cfg(windows)]
-                escape_args: shell.shell_kind() != util::shell::ShellKind::Cmd,
+                escape_args: shell_kind != util::shell::ShellKind::Cmd,
             }
         };
 
@@ -581,7 +583,7 @@ impl TerminalBuilder {
 
         let no_task = task.is_none();
 
-        let mut terminal = Terminal {
+        let terminal = Terminal {
             task,
             terminal_type: TerminalType::Pty {
                 pty_tx: Notifier(pty_tx),
@@ -621,14 +623,23 @@ impl TerminalBuilder {
 
         if !activation_script.is_empty() && no_task {
             for activation_script in activation_script {
-                terminal.input(activation_script.into_bytes());
-                terminal.write_to_pty(if cfg!(windows) {
-                    b"\r\n" as &[_]
-                } else {
-                    b"\n"
-                });
-            }
-            terminal.clear();
+                terminal.write_to_pty(activation_script.into_bytes());
+                // Simulate enter key press
+                // NOTE(PowerShell): using `\r\n` will put PowerShell in a continuation mode (infamous >> character)
+                // and generally mess up the rendering.
+                terminal.write_to_pty(b"\x0d");
+            }
+            // In order to clear the screen at this point, we have two options:
+            // 1. We can send a shell-specific command such as "clear" or "cls"
+            // 2. We can "echo" a marker message that we will then catch when handling a Wakeup event
+            //    and clear the screen using `terminal.clear()` method
+            // We cannot issue a `terminal.clear()` command at this point as alacritty is evented
+            // and while we have sent the activation script to the pty, it will be executed asynchronously.
+            // Therefore, we somehow need to wait for the activation script to finish executing before we
+            // can proceed with clearing the screen.
+            terminal.write_to_pty(shell_kind.clear_screen_command().as_bytes());
+            // Simulate enter key press
+            terminal.write_to_pty(b"\x0d");
         }
 
         Ok(TerminalBuilder {

crates/util/src/shell.rs

@@ -389,4 +389,11 @@ impl ShellKind {
             ShellKind::Posix | ShellKind::Rc => "source",
         }
     }
+
+    pub const fn clear_screen_command(&self) -> &'static str {
+        match self {
+            ShellKind::Cmd => "cls",
+            _ => "clear",
+        }
+    }
 }