Support terminal-wg's BiDi draft proposal in alacritty_terminal

https://terminal-wg.pages.freedesktop.org/bidi

Implementation is hidden behind a `bidi_draft` crate feature, and
depends on alacritty/vte#112.

Public API is limited to:
 * `Cell::bidi_mode()` method which returns a `BidiMode` enum value.
 * `Cell::bidi_box_mirroring()` method which returns a boolean.
 * `Term` boolean field `bidi_disable_arrow_key_swapping`.

Cell `BidiFlags` is only used internally since relations/interactions
between individual flags are not straight forward, and could lead to
erroneous behavior if it's all left for API consumers to figure out.

`BidiDir` named fields exist in all `BidiMode` variants. This is done
deliberately (instead of e.g. a `BidiMode` struct with a `BidiDir` field)
to signify the different purpose `BidiDir` serves in each mode.

Signed-off-by: Mohammad AlSaleh <[email protected]>

alacritty_terminal/Cargo.toml

@@ -12,6 +12,8 @@ rust-version = "1.70.0"
 [features]
 default = ["serde"]
 serde = ["dep:serde", "bitflags/serde", "vte/serde"]
+# Support Bidi/RTL draft proposal from https://terminal-wg.pages.freedesktop.org/bidi
+bidi_draft = []
 
 [dependencies]
 base64 = "0.22.0"
@@ -23,7 +25,7 @@ parking_lot = "0.12.0"
 polling = "3.0.0"
 regex-automata = "0.4.3"
 unicode-width = "0.1"
-vte = { version = "0.13.0", default-features = false, features = ["ansi", "serde"] }
+vte = { git = "https://github.com/MoSal/vte", branch = "scp" , default-features = false, features = ["ansi", "serde"] }
 serde = { version = "1", features = ["derive", "rc"], optional = true }
 
 [target.'cfg(unix)'.dependencies]

alacritty_terminal/src/term/cell.rs

@@ -36,6 +36,97 @@ bitflags! {
  }
 }
 
+#[cfg(feature = "bidi_draft")]
+bitflags! {
+ #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
+ #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+ pub(super) struct BidiFlags: u8 {
+ /// Set with:
+ /// `CSI 8 l`
+ ///
+ /// Reset with:
+ /// `CSI 8 h`
+ ///
+ /// Yes, the default is the high state (implicit mode).
+ const EXPLICIT_DIRECTION = 0b0000_0001;
+ /// Set with:
+ /// `CSI 2 SPACE k` (RTL).
+ /// `CSI 1 SPACE k` (LTR)
+ ///
+ /// Reset with:
+ /// `CSI 0 SPACE k` (default)
+ /// `CSI SPACE k` (default)
+ ///
+ /// Default paragraph direction is not to be confused with
+ /// auto-detection. The default is implementation defined, and
+ /// is often LTR.
+ const NON_DEFAULT_PARA_DIR = 0b0000_0010;
+ /// Set with:
+ /// `CSI 2 SPACE k` (RTL)
+ ///
+ /// Reset with with:
+ /// `CSI 1 SPACE k` (LTR)
+ ///
+ /// Only in effect when `NON_DEFAULT_PARA_DIR` is set.
+ /// Only acts as fallback when `AUTO_PARA_DIR` is set.
+ const RTL_PARA_DIR = 0b0000_0100;
+ /// Set with:
+ /// `CSI ? 2501 h` (auto)
+ ///
+ /// Reset with:
+ /// `CSI ? 2501 l` (default or RTL/LTR)
+ ///
+ /// Set auto direction for paragraphs, based on their content's detected direction.
+ /// Implicit paragraph direction is used if no specific direction is detected.
+ /// This is ignored if `EXPLICIT_DIRECTION` is set.
+ const AUTO_PARA_DIR = 0b0000_1000;
+
+ /// Set with:
+ /// `CSI ? 2500 h` (mirroring)
+ ///
+ /// Reset with:
+ /// `CSI ? 2500 l` (no mirroring)
+ ///
+ /// Use mirrored glyphs of characters from the box drawing block
+ /// (U+2500 - U+257F) in RTL spans.
+ ///
+ /// Visually mirror-able characters from that range don't have the `Bidi_Mirrored` property
+ /// set. So a Bidi-aware shaper/renderer wouldn't mirror them on its own when detected in
+ /// RTL spans.
+ ///
+ /// More info:
+ /// https://www.unicode.org/reports/tr9/#Mirroring
+ /// https://www.unicode.org/reports/tr9/#HL6
+ ///
+ /// Note that this will have an effect in RTL spans, irregardless of paragraph direction.
+ const BOX_MIRRORING = 0b0001_0000;
+ }
+}
+
+#[cfg(feature = "bidi_draft")]
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum BidiDir {
+ LTR,
+ RTL,
+ // Terminal-defined
+ Default,
+}
+
+#[cfg(feature = "bidi_draft")]
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum BidiMode {
+ Explicit { forced_dir: BidiDir },
+ Implicit { para_dir: BidiDir },
+ Auto { fallback_para_dir: BidiDir },
+}
+
+#[cfg(feature = "bidi_draft")]
+impl Default for BidiMode {
+ fn default() -> Self {
+ Self::Implicit { para_dir: BidiDir::Default }
+ }
+}
+
 /// Counter for hyperlinks without explicit ID.
 static HYPERLINK_ID_SUFFIX: AtomicU32 = AtomicU32::new(0);
 
@@ -128,6 +219,9 @@ pub struct CellExtra {
  underline_color: Option<Color>,
 
  hyperlink: Option<Hyperlink>,
+
+ #[cfg(feature = "bidi_draft")]
+ pub(super) bidi_flags: BidiFlags,
 }
 
 /// Content and attributes of a single cell in the terminal grid.
@@ -222,6 +316,67 @@ impl Cell {
  }
 }
 
+#[cfg(feature = "bidi_draft")]
+impl Cell {
+ pub(super) fn remove_bidi_flag(&mut self, bidi_flag: BidiFlags) {
+ self.extra.as_mut().map(|extra| Arc::make_mut(extra).bidi_flags.remove(bidi_flag));
+ let is_default_inner =
+ self.extra.as_deref().map(|extra| *extra == Default::default()).unwrap_or(false);
+ if is_default_inner {
+ self.extra = None;
+ }
+ }
+
+ pub(super) fn insert_bidi_flag(&mut self, bidi_flag: BidiFlags) {
+ if bidi_flag.is_empty() && self.extra.is_none() {
+ return;
+ }
+
+ let extra = self.extra.get_or_insert(Default::default());
+ Arc::make_mut(extra).bidi_flags.insert(bidi_flag);
+ }
+
+ #[inline]
+ pub(super) fn set_bidi_flags(&mut self, bidi_flags: BidiFlags) {
+ if bidi_flags.is_empty() && self.extra.is_none() {
+ return;
+ }
+
+ let extra = self.extra.get_or_insert(Default::default());
+ Arc::make_mut(extra).bidi_flags = bidi_flags;
+ }
+
+ #[inline]
+ pub(super) fn bidi_flags(&self) -> BidiFlags {
+ self.extra.as_ref().map(|extra| extra.bidi_flags).unwrap_or_default()
+ }
+
+ #[inline]
+ pub fn bidi_mode(&self) -> BidiMode {
+ let bidi_flags = self.bidi_flags();
+ let dir = if !bidi_flags.contains(BidiFlags::NON_DEFAULT_PARA_DIR) {
+ BidiDir::Default
+ } else if bidi_flags.contains(BidiFlags::RTL_PARA_DIR) {
+ BidiDir::RTL
+ } else {
+ BidiDir::LTR
+ };
+
+ if bidi_flags.contains(BidiFlags::EXPLICIT_DIRECTION) {
+ BidiMode::Explicit { forced_dir: dir }
+ } else if bidi_flags.contains(BidiFlags::AUTO_PARA_DIR) {
+ BidiMode::Auto { fallback_para_dir: dir }
+ } else {
+ BidiMode::Implicit { para_dir: dir }
+ }
+ }
+
+ #[inline]
+ pub fn bidi_box_mirroring(&self) -> bool {
+ self.bidi_flags().contains(BidiFlags::BOX_MIRRORING)
+ }
+}
+
 impl GridCell for Cell {
  #[inline]
  fn is_empty(&self) -> bool {