FEATURE: Allow ScrollByPage f64 values

`ScrollByPage` can accept non-integer values in the configuration.
This allows fractional page scrolling, such as by half a page.

The default remains the same, at 1 page.

Cargo.lock

@@ -683,6 +683,7 @@ dependencies = [
  "mlua",
  "notify",
  "open",
+ "ordered-float",
  "portable-pty",
  "pretty_env_logger",
  "promise",
@@ -2674,6 +2675,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7940cf2ca942593318d07fcf2596cdca60a85c9e7fab408a5e21a4f9dcd40d87"
 dependencies = [
  "num-traits",
+ "serde",
 ]
 
 [[package]]

config/Cargo.toml

@@ -29,6 +29,7 @@ mlua = {version="0.7", features=["vendored", "lua54", "async", "send"]}
 # file change notification
 notify = "4.0"
 open = "2.0"
+ordered-float = { version = "2.10", features = ["serde"] }
 portable-pty = { path = "../pty", features = ["serde_support"]}
 promise = { path = "../promise" }
 serde = {version="1.0", features = ["rc", "derive"]}

config/src/keyassignment.rs

@@ -1,7 +1,9 @@
+use crate::de_notnan;
 use crate::keys::KeyNoAction;
 use crate::ConfigHandle;
 use crate::LeaderKey;
 use luahelper::impl_lua_conversion;
+use ordered_float::NotNan;
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::path::PathBuf;
@@ -220,7 +222,8 @@ pub enum KeyAssignment {
     ReloadConfiguration,
     MoveTabRelative(isize),
     MoveTab(usize),
-    ScrollByPage(isize),
+    #[serde(deserialize_with = "de_notnan")]
+    ScrollByPage(NotNan<f64>),
     ScrollByLine(isize),
     ScrollToPrompt(isize),
     ScrollToTop,
@@ -554,11 +557,15 @@ impl InputMap {
                     KeyCode::Physical(PhysKeyCode::PageDown),
                     MoveTabRelative(1)
                 ],
-                [Modifiers::SHIFT, KeyCode::PageUp, ScrollByPage(-1)],
+                [
+                    Modifiers::SHIFT,
+                    KeyCode::PageUp,
+                    ScrollByPage(NotNan::new(-1.0).unwrap())
+                ],
                 [
                     Modifiers::SHIFT,
                     KeyCode::Physical(PhysKeyCode::PageDown),
-                    ScrollByPage(1)
+                    ScrollByPage(NotNan::new(1.0).unwrap())
                 ],
                 [
                     Modifiers::ALT,

config/src/lib.rs

@@ -4,6 +4,7 @@ use anyhow::{anyhow, bail, Context, Error};
 use lazy_static::lazy_static;
 use luahelper::impl_lua_conversion;
 use mlua::Lua;
+use ordered_float::NotNan;
 use serde::{Deserialize, Deserializer, Serialize};
 use smol::channel::{Receiver, Sender};
 use smol::prelude::*;
@@ -661,6 +662,14 @@ impl std::ops::Deref for ConfigHandle {
     }
 }
 
+pub(crate) fn de_notnan<'de, D>(deserializer: D) -> Result<NotNan<f64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let value: f64 = de_number(deserializer)?;
+    NotNan::new(value).map_err(|err| serde::de::Error::custom(err.to_string()))
+}
+
 /// Deserialize either an integer or a float as a float
 pub(crate) fn de_number<'de, D>(deserializer: D) -> Result<f64, D::Error>
 where

docs/config/lua/keyassignment/ScrollByPage.md

@@ -14,4 +14,18 @@ return {
 }
 ```
 
+*Since: nightly builds only*
 
+You may now use floating point values to scroll by partial pages.  This example shows
+how to make the `PageUp`/`PageDown` scroll by half a page at a time:
+
+```lua
+local wezterm = require 'wezterm';
+
+return {
+  keys = {
+    {key="PageUp", mods="SHIFT", action=wezterm.action{ScrollByPage=-0.5}},
+    {key="PageDown", mods="SHIFT", action=wezterm.action{ScrollByPage=0.5}},
+  }
+}
+```

wezterm-gui/src/termwindow/mod.rs

@@ -1756,7 +1756,7 @@ impl TermWindow {
         Ok(())
     }
 
-    fn scroll_by_page(&mut self, amount: isize) -> anyhow::Result<()> {
+    fn scroll_by_page(&mut self, amount: f64) -> anyhow::Result<()> {
         let pane = match self.get_active_pane_or_overlay() {
             Some(pane) => pane,
             None => return Ok(()),
@@ -1764,9 +1764,9 @@ impl TermWindow {
         let dims = pane.get_dimensions();
         let position = self
             .get_viewport(pane.pane_id())
-            .unwrap_or(dims.physical_top)
-            .saturating_add(amount * dims.viewport_rows as isize);
-        self.set_viewport(pane.pane_id(), Some(position), dims);
+            .unwrap_or(dims.physical_top) as f64
+            + (amount * dims.viewport_rows as f64);
+        self.set_viewport(pane.pane_id(), Some(position as isize), dims);
         if let Some(win) = self.window.as_ref() {
             win.invalidate();
         }
@@ -1925,7 +1925,7 @@ impl TermWindow {
             ReloadConfiguration => config::reload(),
             MoveTab(n) => self.move_tab(*n)?,
             MoveTabRelative(n) => self.move_tab_relative(*n)?,
-            ScrollByPage(n) => self.scroll_by_page(*n)?,
+            ScrollByPage(n) => self.scroll_by_page(**n)?,
             ScrollByLine(n) => self.scroll_by_line(*n)?,
             ScrollToPrompt(n) => self.scroll_to_prompt(*n)?,
             ScrollToTop => self.scroll_to_top(pane),