Better behaviour on resize (#675)

* First shot at resolving the resizing issues with terminals

* Comment for known bug

* Checking the start row repeatedly to see how it affects performance

---------

Co-authored-by: Daniel Somerfield <daniel.somerfield@hatchdata.com>

src/painting/painter.rs

@@ -82,7 +82,7 @@ impl Painter {
 
     /// Returns the available lines from the prompt down
     pub fn remaining_lines(&self) -> u16 {
-        self.screen_height() - self.prompt_start_row
+        self.screen_height().saturating_sub(self.prompt_start_row)
     }
 
     /// Sets the prompt origin position and screen size for a new line editor
@@ -151,8 +151,14 @@ impl Painter {
         // Marking the painter state as larger buffer to avoid animations
         self.large_buffer = required_lines >= screen_height;
 
+        // This might not be terribly performant. Testing it out
+        let is_reset = || match cursor::position() {
+            Ok(position) => position.1 < self.prompt_start_row,
+            Err(_) => false,
+        };
+
         // Moving the start position of the cursor based on the size of the required lines
-        if self.large_buffer {
+        if self.large_buffer || is_reset() {
             self.prompt_start_row = 0;
         } else if required_lines >= remaining_lines {
             let extra = required_lines.saturating_sub(remaining_lines);
@@ -400,31 +406,22 @@ impl Painter {
 
     /// Updates prompt origin and offset to handle a screen resize event
     pub(crate) fn handle_resize(&mut self, width: u16, height: u16) {
-        let prev_terminal_size = self.terminal_size;
-        let prev_prompt_row = self.prompt_start_row;
-
         self.terminal_size = (width, height);
 
-        if prev_prompt_row < height
-            && height <= prev_terminal_size.1
-            && width == prev_terminal_size.0
-        {
-            // The terminal got smaller in height but the start of the prompt is still visible
-            // The width didn't change
-            return;
+        // `cursor::position() is blocking and can timeout.
+        // The question is whether we can afford it. If not, perhaps we should use it in some scenarios but not others
+        // The problem is trying to calculate this internally doesn't seem to be reliable because terminals might
+        // have additional text in their buffer that messes with the offset on scroll.
+        // It seems like it _should_ be ok because it only happens on resize.
+
+        // Known bug: on iterm2 and kitty, clearing the screen via CMD-K doesn't reset
+        // the position. Might need to special-case this.
+        //
+        // I assume this is a bug with the position() call but haven't figured that
+        // out yet.
+        if let Ok(position) = cursor::position() {
+            self.prompt_start_row = position.1;
         }
-
-        // Either:
-        // - The terminal got larger in height
-        //   - Note: if the terminal doesn't have sufficient history, this will leave a trail
-        //     of previous prompts currently.
-        //   - Note: if the the prompt contains multiple lines, this will leave a trail of
-        //     previous prompts currently.
-        // - The terminal got smaller in height and the whole prompt is no longer visible
-        //   - Note: if the the prompt contains multiple lines, this will leave a trail of
-        //     previous prompts currently.
-        // - The width changed
-        self.prompt_start_row = height.saturating_sub(1);
     }
 
     /// Writes `line` to the terminal with a following carriage return and newline

src/painting/prompt_lines.rs

@@ -7,6 +7,7 @@ use crate::{
 use std::borrow::Cow;
 
 /// Aggregate of prompt and input string used by `Painter`
+#[derive(Debug)]
 pub(crate) struct PromptLines<'prompt> {
     pub(crate) prompt_str_left: Cow<'prompt, str>,
     pub(crate) prompt_str_right: Cow<'prompt, str>,