Add support for alternate scroll escape

Fixes #2727.

8 files changed, 54 insertions, 38 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44d36a41..efdd7bbc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Live reload font size from config
 - New CLI flag `--hold` for keeping Alacritty opened after its child process exits
 - Escape sequence to save and restore window title from stack
+- Alternate scroll escape sequence (`CSI ? 1007 h` / `CSI ? 1007 l`)
 
 ### Changed
 
@@ -76,6 +77,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Bindings for Super/Command + F1-F12
 - Automatic config generation
+- Deprecated `scrolling.faux_multiplier`, the alternate scroll escape can now be used to disable it
+    and `scrolling.multiplier` controls the number of scrolled lines
 
 ## 0.3.3
 
diff --git a/alacritty.yml b/alacritty.yml
index 1b709d65..5e9ca2af 100644
--- a/alacritty.yml
+++ b/alacritty.yml
@@ -87,15 +87,6 @@
   # scrollback is enabled (history > 0).
   #multiplier: 3
 
-  # Faux Scrolling
-  #
-  # The `faux_multiplier` setting controls the number of lines the terminal
-  # should scroll when the alternate screen buffer is active. This is used
-  # to allow mouse scrolling for applications like `man`.
-  #
-  # Specifying `0` will disable faux scrolling.
-  #faux_multiplier: 3
-
   # Scroll to the bottom when new text is written to the terminal.
   #auto_scroll: false
 
diff --git a/alacritty/src/config/mod.rs b/alacritty/src/config/mod.rs
index 8b881fca..beaffd87 100644
--- a/alacritty/src/config/mod.rs
+++ b/alacritty/src/config/mod.rs
@@ -202,6 +202,15 @@ fn print_deprecation_warnings(config: &Config) {
             "Config persistent_logging is deprecated; please use debug.persistent_logging instead"
         );
     }
+
+    if config.scrolling.faux_multiplier().is_some() {
+        warn!(
+            target: LOG_TARGET_CONFIG,
+            "Config scrolling.faux_multiplier is deprecated; the alternate scroll escape can now \
+             be used to disable it and `scrolling.multiplier` controls the number of scrolled \
+             lines"
+        );
+    }
 }
 
 #[cfg(test)]
diff --git a/alacritty/src/input.rs b/alacritty/src/input.rs
index be6a030e..a3148820 100644
--- a/alacritty/src/input.rs
+++ b/alacritty/src/input.rs
@@ -551,11 +551,9 @@ impl<'a, T: EventListener, A: ActionContext<T> + 'a> Processor<'a, T, A> {
     fn scroll_terminal(&mut self, modifiers: ModifiersState, new_scroll_px: i32) {
         let mouse_modes =
             TermMode::MOUSE_REPORT_CLICK | TermMode::MOUSE_DRAG | TermMode::MOUSE_MOTION;
+        let alt_scroll_modes = TermMode::ALT_SCREEN | TermMode::ALTERNATE_SCROLL;
         let height = self.ctx.size_info().cell_height as i32;
 
-        // Make sure the new and deprecated setting are both allowed
-        let faux_multiplier = self.config.scrolling.faux_multiplier() as usize;
-
         if self.ctx.terminal().mode().intersects(mouse_modes) {
             self.ctx.mouse_mut().scroll_px += new_scroll_px;
 
@@ -565,11 +563,14 @@ impl<'a, T: EventListener, A: ActionContext<T> + 'a> Processor<'a, T, A> {
             for _ in 0..lines {
                 self.mouse_report(code, ElementState::Pressed, modifiers);
             }
-        } else if self.ctx.terminal().mode().contains(TermMode::ALT_SCREEN)
-            && faux_multiplier > 0
-            && !modifiers.shift
-        {
-            self.ctx.mouse_mut().scroll_px += new_scroll_px * faux_multiplier as i32;
+        } else if self.ctx.terminal().mode().contains(alt_scroll_modes) && !modifiers.shift {
+            let multiplier = i32::from(
+                self.config
+                    .scrolling
+                    .faux_multiplier()
+                    .unwrap_or_else(|| self.config.scrolling.multiplier()),
+            );
+            self.ctx.mouse_mut().scroll_px += new_scroll_px * multiplier;
 
             let cmd = if new_scroll_px > 0 { b'A' } else { b'B' };
             let lines = (self.ctx.mouse().scroll_px / height).abs();
diff --git a/alacritty/src/logging.rs b/alacritty/src/logging.rs
index ea44637b..9d837a78 100644
--- a/alacritty/src/logging.rs
+++ b/alacritty/src/logging.rs
@@ -172,7 +172,8 @@ impl OnDemandLogFile {
                 Ok(file) => {
                     self.file = Some(io::LineWriter::new(file));
                     self.created.store(true, Ordering::Relaxed);
-                    let _ = writeln!(io::stdout(), "Created log file at \"{}\"", self.path.display());
+                    let _ =
+                        writeln!(io::stdout(), "Created log file at \"{}\"", self.path.display());
                 },
                 Err(e) => {
                     let _ = writeln!(io::stdout(), "Unable to create log file: {}", e);
diff --git a/alacritty_terminal/src/ansi.rs b/alacritty_terminal/src/ansi.rs
index 493b02aa..d989b78e 100644
--- a/alacritty_terminal/src/ansi.rs
+++ b/alacritty_terminal/src/ansi.rs
@@ -408,6 +408,8 @@ pub enum Mode {
     ReportFocusInOut = 1004,
     /// ?1006
     SgrMouse = 1006,
+    /// ?1007
+    AlternateScroll = 1007,
     /// ?1049
     SwapScreenAndSetRestoreCursor = 1049,
     /// ?2004
@@ -438,6 +440,7 @@ impl Mode {
                 1003 => Mode::ReportAllMouseMotion,
                 1004 => Mode::ReportFocusInOut,
                 1006 => Mode::SgrMouse,
+                1007 => Mode::AlternateScroll,
                 1049 => Mode::SwapScreenAndSetRestoreCursor,
                 2004 => Mode::BracketedPaste,
                 _ => {
diff --git a/alacritty_terminal/src/config/scrolling.rs b/alacritty_terminal/src/config/scrolling.rs
index 8471fcd7..1746266f 100644
--- a/alacritty_terminal/src/config/scrolling.rs
+++ b/alacritty_terminal/src/config/scrolling.rs
@@ -12,9 +12,11 @@ pub struct Scrolling {
     #[serde(deserialize_with = "failure_default")]
     multiplier: ScrollingMultiplier,
     #[serde(deserialize_with = "failure_default")]
-    faux_multiplier: ScrollingMultiplier,
-    #[serde(deserialize_with = "failure_default")]
     pub auto_scroll: bool,
+
+    // TODO: DEPRECATED
+    #[serde(deserialize_with = "failure_default")]
+    faux_multiplier: Option<ScrollingMultiplier>,
 }
 
 impl Scrolling {
@@ -26,8 +28,8 @@ impl Scrolling {
         self.multiplier.0
     }
 
-    pub fn faux_multiplier(self) -> u8 {
-        self.faux_multiplier.0
+    pub fn faux_multiplier(self) -> Option<u8> {
+        self.faux_multiplier.map(|sm| sm.0)
     }
 
     // Update the history size, used in ref tests
diff --git a/alacritty_terminal/src/term/mod.rs b/alacritty_terminal/src/term/mod.rs
index 382b10a9..bc7235cb 100644
--- a/alacritty_terminal/src/term/mod.rs
+++ b/alacritty_terminal/src/term/mod.rs
@@ -457,28 +457,29 @@ pub mod mode {
 
     bitflags! {
         pub struct TermMode: u16 {
-            const SHOW_CURSOR         = 0b00_0000_0000_0001;
-            const APP_CURSOR          = 0b00_0000_0000_0010;
-            const APP_KEYPAD          = 0b00_0000_0000_0100;
-            const MOUSE_REPORT_CLICK  = 0b00_0000_0000_1000;
-            const BRACKETED_PASTE     = 0b00_0000_0001_0000;
-            const SGR_MOUSE           = 0b00_0000_0010_0000;
-            const MOUSE_MOTION        = 0b00_0000_0100_0000;
-            const LINE_WRAP           = 0b00_0000_1000_0000;
-            const LINE_FEED_NEW_LINE  = 0b00_0001_0000_0000;
-            const ORIGIN              = 0b00_0010_0000_0000;
-            const INSERT              = 0b00_0100_0000_0000;
-            const FOCUS_IN_OUT        = 0b00_1000_0000_0000;
-            const ALT_SCREEN          = 0b01_0000_0000_0000;
-            const MOUSE_DRAG          = 0b10_0000_0000_0000;
-            const ANY                 = 0b11_1111_1111_1111;
+            const SHOW_CURSOR         = 0b000_0000_0000_0001;
+            const APP_CURSOR          = 0b000_0000_0000_0010;
+            const APP_KEYPAD          = 0b000_0000_0000_0100;
+            const MOUSE_REPORT_CLICK  = 0b000_0000_0000_1000;
+            const BRACKETED_PASTE     = 0b000_0000_0001_0000;
+            const SGR_MOUSE           = 0b000_0000_0010_0000;
+            const MOUSE_MOTION        = 0b000_0000_0100_0000;
+            const LINE_WRAP           = 0b000_0000_1000_0000;
+            const LINE_FEED_NEW_LINE  = 0b000_0001_0000_0000;
+            const ORIGIN              = 0b000_0010_0000_0000;
+            const INSERT              = 0b000_0100_0000_0000;
+            const FOCUS_IN_OUT        = 0b000_1000_0000_0000;
+            const ALT_SCREEN          = 0b001_0000_0000_0000;
+            const MOUSE_DRAG          = 0b010_0000_0000_0000;
+            const ALTERNATE_SCROLL    = 0b100_0000_0000_0000;
+            const ANY                 = 0b111_1111_1111_1111;
             const NONE                = 0;
         }
     }
 
     impl Default for TermMode {
         fn default() -> TermMode {
-            TermMode::SHOW_CURSOR | TermMode::LINE_WRAP
+            TermMode::SHOW_CURSOR | TermMode::LINE_WRAP | TermMode::ALTERNATE_SCROLL
         }
     }
 }
@@ -913,6 +914,9 @@ impl<T> Term<T> {
             }
         }
         self.visual_bell.update_config(config);
+        if let Some(0) = config.scrolling.faux_multiplier() {
+            self.mode.remove(TermMode::ALTERNATE_SCROLL);
+        }
         self.default_cursor_style = config.cursor.style;
         self.dynamic_title = config.dynamic_title();
         self.auto_scroll = config.scrolling.auto_scroll;
@@ -2008,6 +2012,7 @@ impl<T: EventListener> ansi::Handler for Term<T> {
             ansi::Mode::ReportFocusInOut => self.mode.insert(TermMode::FOCUS_IN_OUT),
             ansi::Mode::BracketedPaste => self.mode.insert(TermMode::BRACKETED_PASTE),
             ansi::Mode::SgrMouse => self.mode.insert(TermMode::SGR_MOUSE),
+            ansi::Mode::AlternateScroll => self.mode.insert(TermMode::ALTERNATE_SCROLL),
             ansi::Mode::LineWrap => self.mode.insert(TermMode::LINE_WRAP),
             ansi::Mode::LineFeedNewLine => self.mode.insert(TermMode::LINE_FEED_NEW_LINE),
             ansi::Mode::Origin => self.mode.insert(TermMode::ORIGIN),
@@ -2048,6 +2053,7 @@ impl<T: EventListener> ansi::Handler for Term<T> {
             ansi::Mode::ReportFocusInOut => self.mode.remove(TermMode::FOCUS_IN_OUT),
             ansi::Mode::BracketedPaste => self.mode.remove(TermMode::BRACKETED_PASTE),
             ansi::Mode::SgrMouse => self.mode.remove(TermMode::SGR_MOUSE),
+            ansi::Mode::AlternateScroll => self.mode.remove(TermMode::ALTERNATE_SCROLL),
             ansi::Mode::LineWrap => self.mode.remove(TermMode::LINE_WRAP),
             ansi::Mode::LineFeedNewLine => self.mode.remove(TermMode::LINE_FEED_NEW_LINE),
             ansi::Mode::Origin => self.mode.remove(TermMode::ORIGIN),