From fadf0f2e5bb484e9ae7f8c03f6c0b25aa6994adb Mon Sep 17 00:00:00 2001
From: Johannes Altmanninger <aclopte@gmail.com>
Date: Sat, 2 Dec 2023 18:20:40 +0100
Subject: [PATCH] Port editable_line_t

---
 fish-rust/build.rs                   |   1 +
 fish-rust/src/editable_line.rs       | 426 +++++++++++++++++++++++++++
 fish-rust/src/highlight.rs           |  11 +
 fish-rust/src/lib.rs                 |   1 +
 fish-rust/src/tests/editable_line.rs |  60 ++++
 fish-rust/src/tests/mod.rs           |   2 +
 src/editable_line.h                  |  18 ++
 src/fish_tests.cpp                   |  68 +----
 src/pager.cpp                        |  20 +-
 src/pager.h                          |  11 +-
 src/reader.cpp                       | 373 +++++++----------------
 src/reader.h                         | 112 +------
 12 files changed, 660 insertions(+), 443 deletions(-)
 create mode 100644 fish-rust/src/editable_line.rs
 create mode 100644 fish-rust/src/tests/editable_line.rs
 create mode 100644 src/editable_line.h

diff --git a/fish-rust/build.rs b/fish-rust/build.rs
index c407dd2b5..eb816f545 100644
--- a/fish-rust/build.rs
+++ b/fish-rust/build.rs
@@ -69,6 +69,7 @@ fn main() {
         "fish-rust/src/builtins/shared.rs",
         "fish-rust/src/common.rs",
         "fish-rust/src/complete.rs",
+        "fish-rust/src/editable_line.rs",
         "fish-rust/src/env_dispatch.rs",
         "fish-rust/src/env/env_ffi.rs",
         "fish-rust/src/event.rs",
diff --git a/fish-rust/src/editable_line.rs b/fish-rust/src/editable_line.rs
new file mode 100644
index 000000000..f4427aeb6
--- /dev/null
+++ b/fish-rust/src/editable_line.rs
@@ -0,0 +1,426 @@
+use std::pin::Pin;
+
+use cxx::{CxxWString, UniquePtr};
+
+use crate::future::IsSomeAnd;
+use crate::highlight::{HighlightSpec, HighlightSpecListFFI};
+use crate::wchar::prelude::*;
+use crate::wchar_ffi::{WCharFromFFI, WCharToFFI};
+
+/// An edit action that can be undone.
+#[derive(Clone, Eq, PartialEq)]
+pub struct Edit {
+    /// When undoing the edit we use this to restore the previous cursor position.
+    pub cursor_position_before_edit: usize,
+
+    /// The span of text that is replaced by this edit.
+    pub range: std::ops::Range<usize>,
+
+    /// The strings that are removed and added by this edit, respectively.
+    pub old: WString,
+    pub replacement: WString,
+
+    /// edit_t is only for contiguous changes, so to restore a group of arbitrary changes to the
+    /// command line we need to have a group id as forcibly coalescing changes is not enough.
+    group_id: Option<usize>,
+}
+
+impl Edit {
+    pub fn new(range: std::ops::Range<usize>, replacement: WString) -> Self {
+        Self {
+            cursor_position_before_edit: 0,
+            range,
+            old: WString::new(),
+            replacement,
+            group_id: None,
+        }
+    }
+}
+
+/// Modify a string and its syntax highlighting according to the given edit.
+/// Currently exposed for testing only.
+pub fn apply_edit(target: &mut WString, colors: &mut Vec<HighlightSpec>, edit: &Edit) {
+    let range = &edit.range;
+    target.replace_range(range.clone(), &edit.replacement);
+
+    // Now do the same to highlighting.
+    let last_color = edit
+        .range
+        .start
+        .checked_sub(1)
+        .map(|i| colors[i])
+        .unwrap_or_default();
+    colors.splice(
+        range.clone(),
+        std::iter::repeat(last_color).take(edit.replacement.len()),
+    );
+}
+
+/// The history of all edits to some command line.
+#[derive(Clone, Default)]
+pub struct UndoHistory {
+    /// The stack of edits that can be undone or redone atomically.
+    pub edits: Vec<Edit>,
+
+    /// The position in the undo stack that corresponds to the current
+    /// state of the input line.
+    /// Invariants:
+    ///     edits_applied - 1 is the index of the next edit to undo.
+    ///     edits_applied     is the index of the next edit to redo.
+    ///
+    /// For example, if nothing was undone, edits_applied is edits.size().
+    /// If every single edit was undone, edits_applied is 0.
+    pub edits_applied: usize,
+
+    /// Whether we allow the next edit to be grouped together with the
+    /// last one.
+    may_coalesce: bool,
+
+    /// Whether to be more aggressive in coalescing edits. Ideally, it would be "force coalesce"
+    /// with guaranteed atomicity but as `edit_t` is strictly for contiguous changes, that guarantee
+    /// can't be made at this time.
+    try_coalesce: bool,
+}
+
+impl UndoHistory {
+    /// Empty the history.
+    pub fn clear(&mut self) {
+        self.edits.clear();
+        self.edits_applied = 0;
+        self.may_coalesce = false;
+    }
+}
+
+/// Helper class for storing a command line.
+#[derive(Clone, Default)]
+pub struct EditableLine {
+    /// The command line.
+    text: WString,
+    /// Syntax highlighting.
+    colors: Vec<HighlightSpec>,
+    /// The current position of the cursor in the command line.
+    position: usize,
+
+    /// The history of all edits.
+    undo_history: UndoHistory,
+    /// The nesting level for atomic edits, so that recursive invocations of start_edit_group()
+    /// are not ended by one end_edit_group() call.
+    edit_group_level: Option<usize>,
+    /// Monotonically increasing edit group, ignored when edit_group_level_ is -1. Allowed to wrap.
+    edit_group_id: usize,
+}
+
+impl EditableLine {
+    pub fn text(&self) -> &wstr {
+        &self.text
+    }
+
+    pub fn colors(&self) -> &[HighlightSpec] {
+        &self.colors
+    }
+    pub fn set_colors(&mut self, colors: Vec<HighlightSpec>) {
+        assert_eq!(colors.len(), self.len());
+        self.colors = colors;
+    }
+
+    pub fn position(&self) -> usize {
+        self.position
+    }
+    pub fn set_position(&mut self, position: usize) {
+        self.position = position;
+    }
+
+    // Gets the length of the text.
+    pub fn len(&self) -> usize {
+        self.text.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.text.is_empty()
+    }
+
+    pub fn at(&self, idx: usize) -> char {
+        self.text.char_at(idx)
+    }
+
+    pub fn clear(&mut self) {
+        self.undo_history.clear();
+        if self.is_empty() {
+            return;
+        }
+        let len = self.len();
+        apply_edit(
+            &mut self.text,
+            &mut self.colors,
+            &Edit::new(0..len, L!("").to_owned()),
+        );
+        self.set_position(0);
+    }
+
+    /// Modify the commandline according to @edit. Most modifications to the
+    /// text should pass through this function.
+    pub fn push_edit(&mut self, mut edit: Edit, allow_coalesce: bool) {
+        let range = &edit.range;
+        let is_insertion = range.is_empty();
+        // Coalescing insertion does not create a new undo entry but adds to the last insertion.
+        if allow_coalesce && is_insertion && self.want_to_coalesce_insertion_of(&edit.replacement) {
+            assert!(range.start == self.position());
+            let last_edit = self.undo_history.edits.last_mut().unwrap();
+            last_edit.replacement.push_utfstr(&edit.replacement);
+            apply_edit(&mut self.text, &mut self.colors, &edit);
+            self.set_position(self.position() + edit.replacement.len());
+
+            assert!(self.undo_history.may_coalesce);
+            return;
+        }
+
+        // Assign a new group id or propagate the old one if we're in a logical grouping of edits
+        if self.edit_group_level.is_some() {
+            edit.group_id = Some(self.edit_group_id);
+        }
+
+        let edit_does_nothing = range.is_empty() && edit.replacement.is_empty();
+        if edit_does_nothing {
+            return;
+        }
+        if self.undo_history.edits_applied != self.undo_history.edits.len() {
+            // After undoing some edits, the user is making a new edit;
+            // we are about to create a new edit branch.
+            // Discard all edits that were undone because we only support
+            // linear undo/redo, they will be unreachable.
+            self.undo_history
+                .edits
+                .truncate(self.undo_history.edits_applied);
+        }
+        edit.cursor_position_before_edit = self.position();
+        edit.old = self.text[range.clone()].to_owned();
+        apply_edit(&mut self.text, &mut self.colors, &edit);
+        self.set_position(cursor_position_after_edit(&edit));
+        assert_eq!(
+            self.undo_history.edits_applied,
+            self.undo_history.edits.len()
+        );
+        self.undo_history.may_coalesce =
+            is_insertion && (self.undo_history.try_coalesce || edit.replacement.len() == 1);
+        self.undo_history.edits_applied += 1;
+        self.undo_history.edits.push(edit);
+    }
+
+    /// Undo the most recent edit that was not yet undone. Returns true on success.
+    pub fn undo(&mut self) -> bool {
+        let mut did_undo = false;
+        let mut last_group_id = None;
+        while self.undo_history.edits_applied != 0 {
+            let edit = &self.undo_history.edits[self.undo_history.edits_applied - 1];
+            if did_undo
+                && edit
+                    .group_id
+                    .is_none_or(|group_id| Some(group_id) != last_group_id)
+            {
+                // We've restored all the edits in this logical undo group
+                break;
+            }
+            last_group_id = edit.group_id;
+            self.undo_history.edits_applied -= 1;
+            let range = &edit.range;
+            let mut inverse = Edit::new(
+                range.start..range.start + edit.replacement.len(),
+                L!("").to_owned(),
+            );
+            inverse.replacement = edit.old.clone();
+            let old_position = edit.cursor_position_before_edit;
+            apply_edit(&mut self.text, &mut self.colors, &inverse);
+            self.set_position(old_position);
+            did_undo = true;
+        }
+
+        self.end_edit_group();
+        self.undo_history.may_coalesce = false;
+        did_undo
+    }
+
+    /// Redo the most recent undo. Returns true on success.
+    pub fn redo(&mut self) -> bool {
+        let mut did_redo = false;
+
+        let mut last_group_id = None;
+        while let Some(edit) = self.undo_history.edits.get(self.undo_history.edits_applied) {
+            if did_redo
+                && edit
+                    .group_id
+                    .is_none_or(|group_id| Some(group_id) != last_group_id)
+            {
+                // We've restored all the edits in this logical undo group
+                break;
+            }
+            last_group_id = edit.group_id;
+            self.undo_history.edits_applied += 1;
+            apply_edit(&mut self.text, &mut self.colors, edit);
+            self.set_position(cursor_position_after_edit(edit));
+            did_redo = true;
+        }
+
+        self.end_edit_group();
+        did_redo
+    }
+
+    /// Start a logical grouping of command line edits that should be undone/redone together.
+    pub fn begin_edit_group(&mut self) {
+        if self.edit_group_level.is_some() {
+            return;
+        }
+        self.edit_group_level = Some(55 + 1);
+        // Indicate that the next change must trigger the creation of a new history item
+        self.undo_history.may_coalesce = false;
+        // Indicate that future changes should be coalesced into the same edit if possible.
+        self.undo_history.try_coalesce = true;
+        // Assign a logical edit group id to future edits in this group
+        self.edit_group_id += 1;
+    }
+
+    /// End a logical grouping of command line edits that should be undone/redone together.
+    pub fn end_edit_group(&mut self) {
+        let Some(edit_group_level) = self.edit_group_level.as_mut() else {
+            // Clamp the minimum value to -1 to prevent unbalanced end_edit_group() calls from breaking
+            // everything.
+            return;
+        };
+
+        *edit_group_level -= 1;
+
+        if *edit_group_level == 55 {
+            self.undo_history.try_coalesce = false;
+            self.undo_history.may_coalesce = false;
+        }
+    }
+
+    /// Whether we want to append this string to the previous edit.
+    fn want_to_coalesce_insertion_of(&self, s: &wstr) -> bool {
+        // The previous edit must support coalescing.
+        if !self.undo_history.may_coalesce {
+            return false;
+        }
+        // Only consolidate single character inserts.
+        if s.len() != 1 {
+            return false;
+        }
+        // Make an undo group after every space.
+        if s.as_char_slice()[0] == ' ' && !self.undo_history.try_coalesce {
+            return false;
+        }
+        let last_edit = self.undo_history.edits.last().unwrap();
+        // Don't add to the last edit if it deleted something.
+        if !last_edit.range.is_empty() {
+            return false;
+        }
+        // Must not have moved the cursor!
+        if cursor_position_after_edit(last_edit) != self.position() {
+            return false;
+        }
+        true
+    }
+}
+
+/// Returns the number of characters left of the cursor that are removed by the
+/// deletion in the given edit.
+fn chars_deleted_left_of_cursor(edit: &Edit) -> usize {
+    if edit.cursor_position_before_edit > edit.range.start {
+        return std::cmp::min(
+            edit.range.len(),
+            edit.cursor_position_before_edit - edit.range.start,
+        );
+    }
+    0
+}
+
+/// Compute the position of the cursor after the given edit.
+fn cursor_position_after_edit(edit: &Edit) -> usize {
+    let cursor = edit.cursor_position_before_edit + edit.replacement.len();
+    let removed = chars_deleted_left_of_cursor(edit);
+    cursor.saturating_sub(removed)
+}
+
+#[cxx::bridge]
+mod editable_line_ffi {
+    extern "C++" {
+        include!("editable_line.h");
+        include!("highlight.h");
+        pub type HighlightSpec = crate::highlight::HighlightSpec;
+        pub type HighlightSpecListFFI = crate::highlight::HighlightSpecListFFI;
+    }
+    extern "Rust" {
+        type Edit;
+        fn new_edit(start: usize, end: usize, replacement: &CxxWString) -> Box<Edit>;
+        #[cxx_name = "apply_edit"]
+        fn apply_edit_ffi(
+            target: &CxxWString,
+            mut colors: Pin<&mut HighlightSpecListFFI>,
+            edit: Box<Edit>,
+        ) -> UniquePtr<CxxWString>;
+    }
+    extern "Rust" {
+        type UndoHistory;
+    }
+    extern "Rust" {
+        type EditableLine;
+        fn new_editable_line() -> Box<EditableLine>;
+        fn empty(&self) -> bool;
+        #[cxx_name = "text"]
+        fn text_ffi(&self) -> UniquePtr<CxxWString>;
+        #[cxx_name = "clone"]
+        fn clone_ffi(&self) -> Box<EditableLine>;
+        fn position(&self) -> usize;
+        fn set_position(&mut self, position: usize);
+        fn clear(&mut self);
+        fn undo(&mut self) -> bool;
+        fn redo(&mut self) -> bool;
+        fn size(&self) -> usize;
+        #[cxx_name = "push_edit"]
+        fn push_edit_ffi(&mut self, edit: Box<Edit>, allow_coalesce: bool);
+        fn begin_edit_group(&mut self);
+        fn end_edit_group(&mut self);
+        #[cxx_name = "at"]
+        fn at_ffi(&self, index: usize) -> u32;
+        #[cxx_name = "set_colors"]
+        fn set_colors_ffi(&mut self, colors: &HighlightSpecListFFI);
+    }
+}
+fn new_edit(start: usize, end: usize, replacement: &CxxWString) -> Box<Edit> {
+    Box::new(Edit::new(start..end, replacement.from_ffi()))
+}
+fn new_editable_line() -> Box<EditableLine> {
+    Box::default()
+}
+impl EditableLine {
+    fn empty(&self) -> bool {
+        self.is_empty()
+    }
+    fn text_ffi(&self) -> UniquePtr<CxxWString> {
+        self.text().to_ffi()
+    }
+    fn clone_ffi(&self) -> Box<Self> {
+        Box::new(self.clone())
+    }
+    fn size(&self) -> usize {
+        self.len()
+    }
+    #[allow(clippy::boxed_local)]
+    fn push_edit_ffi(&mut self, edit: Box<Edit>, allow_coalesce: bool) {
+        self.push_edit(*edit, allow_coalesce);
+    }
+    fn at_ffi(&self, index: usize) -> u32 {
+        self.at(index) as _
+    }
+    fn set_colors_ffi(&mut self, colors: &HighlightSpecListFFI) {
+        self.set_colors(colors.0.clone())
+    }
+}
+fn apply_edit_ffi(
+    target: &CxxWString,
+    mut colors: Pin<&mut HighlightSpecListFFI>,
+    edit: Box<Edit>,
+) -> UniquePtr<CxxWString> {
+    let mut target = target.from_ffi();
+    apply_edit(&mut target, &mut colors.0, &edit);
+    target.to_ffi()
+}
diff --git a/fish-rust/src/highlight.rs b/fish-rust/src/highlight.rs
index e40010166..8b6bb82bf 100644
--- a/fish-rust/src/highlight.rs
+++ b/fish-rust/src/highlight.rs
@@ -11,6 +11,7 @@
     EXPAND_RESERVED_BASE, EXPAND_RESERVED_END,
 };
 use crate::compat::_PC_CASE_SENSITIVE;
+use crate::editable_line::EditableLine;
 use crate::env::{EnvStackRefFFI, Environment};
 use crate::expand::{
     expand_one, expand_tilde, expand_to_command_and_args, ExpandFlags, ExpandResultCode,
@@ -1681,6 +1682,7 @@ pub struct HighlightSpec {
         #[cxx_name = "clone"]
         fn clone_ffi(self: &HighlightSpec) -> Box<HighlightSpec>;
         fn new_highlight_spec() -> Box<HighlightSpec>;
+        fn editable_line_colors(editable_line: &EditableLine) -> &[HighlightSpec];
     }
 
     extern "C++" {
@@ -1688,6 +1690,7 @@ pub struct HighlightSpec {
         include!("history.h");
         include!("color.h");
         include!("operation_context.h");
+        include!("editable_line.h");
         type HistoryItem = crate::history::HistoryItem;
         type OperationContext<'a> = crate::operation_context::OperationContext<'a>;
         type rgb_color_t = crate::ffi::rgb_color_t;
@@ -1695,6 +1698,7 @@ pub struct HighlightSpec {
         type EnvDynFFI = crate::env::EnvDynFFI;
         #[cxx_name = "EnvStackRef"]
         type EnvStackRefFFI = crate::env::EnvStackRefFFI;
+        type EditableLine = crate::editable_line::EditableLine;
     }
     extern "Rust" {
         #[cxx_name = "autosuggest_validate_from_history"]
@@ -1838,3 +1842,10 @@ fn clone_ffi(&self) -> Box<HighlightSpec> {
 fn new_highlight_spec() -> Box<HighlightSpec> {
     Box::default()
 }
+unsafe impl cxx::ExternType for EditableLine {
+    type Id = cxx::type_id!("EditableLine");
+    type Kind = cxx::kind::Opaque;
+}
+fn editable_line_colors(editable_line: &EditableLine) -> &[HighlightSpec] {
+    editable_line.colors()
+}
diff --git a/fish-rust/src/lib.rs b/fish-rust/src/lib.rs
index 950d38419..7c4cba543 100644
--- a/fish-rust/src/lib.rs
+++ b/fish-rust/src/lib.rs
@@ -35,6 +35,7 @@
 mod compat;
 mod complete;
 mod curses;
+mod editable_line;
 mod env;
 mod env_dispatch;
 mod env_universal_common;
diff --git a/fish-rust/src/tests/editable_line.rs b/fish-rust/src/tests/editable_line.rs
new file mode 100644
index 000000000..7b8c66a18
--- /dev/null
+++ b/fish-rust/src/tests/editable_line.rs
@@ -0,0 +1,60 @@
+use crate::{
+    editable_line::{Edit, EditableLine},
+    wchar::prelude::*,
+};
+
+#[test]
+fn test_undo() {
+    let mut line = EditableLine::default();
+
+    let insert = |line: &EditableLine| line.position()..line.position();
+
+    assert!(!line.undo()); // nothing to undo
+    assert!(line.text().is_empty());
+    assert_eq!(line.position(), 0);
+    line.push_edit(Edit::new(0..0, L!("a b c").to_owned()), true);
+    assert_eq!(line.text(), L!("a b c").to_owned());
+    assert_eq!(line.position(), 5);
+    line.set_position(2);
+    line.push_edit(Edit::new(2..3, L!("B").to_owned()), true); // replacement right of cursor
+    assert_eq!(line.text(), L!("a B c").to_owned());
+    line.undo();
+    assert_eq!(line.text(), L!("a b c").to_owned());
+    assert_eq!(line.position(), 2);
+    line.redo();
+    assert_eq!(line.text(), L!("a B c").to_owned());
+    assert_eq!(line.position(), 3);
+
+    assert!(!line.redo()); // nothing to redo
+
+    line.push_edit(Edit::new(0..2, L!("").to_owned()), true); // deletion left of cursor
+    assert_eq!(line.text(), L!("B c").to_owned());
+    assert_eq!(line.position(), 1);
+    line.undo();
+    assert_eq!(line.text(), L!("a B c").to_owned());
+    assert_eq!(line.position(), 3);
+    line.redo();
+    assert_eq!(line.text(), L!("B c").to_owned());
+    assert_eq!(line.position(), 1);
+
+    line.push_edit(Edit::new(0..line.len(), L!("a b c").to_owned()), true); // replacement left and right of cursor
+    assert_eq!(line.text(), L!("a b c").to_owned());
+    assert_eq!(line.position(), 5);
+
+    // Undo coalesced edits
+    line.clear();
+    line.push_edit(Edit::new(insert(&line), L!("a").to_owned()), true);
+    line.push_edit(Edit::new(insert(&line), L!("b").to_owned()), true);
+    line.push_edit(Edit::new(insert(&line), L!("c").to_owned()), true);
+    line.push_edit(Edit::new(insert(&line), L!(" ").to_owned()), true);
+    line.undo();
+    line.undo();
+    line.redo();
+    assert_eq!(line.text(), L!("abc").to_owned());
+    // This removes the space insertion from the history, but does not coalesce with the first edit.
+    line.push_edit(Edit::new(insert(&line), L!("d").to_owned()), true);
+    line.push_edit(Edit::new(insert(&line), L!("e").to_owned()), true);
+    assert_eq!(line.text(), L!("abcde").to_owned());
+    line.undo();
+    assert_eq!(line.text(), L!("abc").to_owned());
+}
diff --git a/fish-rust/src/tests/mod.rs b/fish-rust/src/tests/mod.rs
index 2cf179658..2b871d78a 100644
--- a/fish-rust/src/tests/mod.rs
+++ b/fish-rust/src/tests/mod.rs
@@ -3,6 +3,8 @@
 #[cfg(test)]
 mod common;
 mod complete;
+#[cfg(test)]
+mod editable_line;
 mod env;
 mod env_universal_common;
 mod expand;
diff --git a/src/editable_line.h b/src/editable_line.h
new file mode 100644
index 000000000..c0852a295
--- /dev/null
+++ b/src/editable_line.h
@@ -0,0 +1,18 @@
+#ifndef FISH_EDITABLE_LINE_H
+#define FISH_EDITABLE_LINE_H
+
+struct HighlightSpecListFFI;
+
+#if INCLUDE_RUST_HEADERS
+#include "editable_line.rs.h"
+#else
+struct Edit;
+struct UndoHistory;
+struct EditableLine;
+#endif
+
+using edit_t = Edit;
+using undo_history_t = UndoHistory;
+using editable_line_t = EditableLine;
+
+#endif
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index d412e9b91..e2fe11b7a 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -1110,7 +1110,17 @@ static void test_abbreviations() {
                 cmdline, cursor_pos.value_or(cmdline.size()), parser_principal_parser()->deref())) {
             wcstring cmdline_expanded = cmdline;
             std::vector<highlight_spec_t> colors{cmdline_expanded.size()};
-            apply_edit(&cmdline_expanded, &colors, edit_t{replacement->range, *replacement->text});
+            auto ffi_colors = new_highlight_spec_list();
+            for (auto &c : colors) {
+                ffi_colors->push(c);
+            }
+            cmdline_expanded = *apply_edit(
+                cmdline_expanded, *ffi_colors,
+                new_edit(replacement->range.start, replacement->range.end(), *replacement->text));
+            colors.clear();
+            for (size_t i = 0; i < ffi_colors->size(); i++) {
+                colors.push_back(ffi_colors->at(i));
+            }
             return cmdline_expanded;
         }
         return none_t();
@@ -1604,61 +1614,6 @@ static void test_input() {
     }
 }
 
-// todo!("port this")
-static void test_undo() {
-    say(L"Testing undo/redo setting and restoring text and cursor position.");
-
-    editable_line_t line;
-    do_test(!line.undo());  // nothing to undo
-    do_test(line.text().empty());
-    do_test(line.position() == 0);
-    line.push_edit(edit_t(0, 0, L"a b c"), true);
-    do_test(line.text() == L"a b c");
-    do_test(line.position() == 5);
-    line.set_position(2);
-    line.push_edit(edit_t(2, 1, L"B"), true);  // replacement right of cursor
-    do_test(line.text() == L"a B c");
-    line.undo();
-    do_test(line.text() == L"a b c");
-    do_test(line.position() == 2);
-    line.redo();
-    do_test(line.text() == L"a B c");
-    do_test(line.position() == 3);
-
-    do_test(!line.redo());  // nothing to redo
-
-    line.push_edit(edit_t(0, 2, L""), true);  // deletion left of cursor
-    do_test(line.text() == L"B c");
-    do_test(line.position() == 1);
-    line.undo();
-    do_test(line.text() == L"a B c");
-    do_test(line.position() == 3);
-    line.redo();
-    do_test(line.text() == L"B c");
-    do_test(line.position() == 1);
-
-    line.push_edit(edit_t(0, line.size(), L"a b c"), true);  // replacement left and right of cursor
-    do_test(line.text() == L"a b c");
-    do_test(line.position() == 5);
-
-    say(L"Testing undoing coalesced edits.");
-    line.clear();
-    line.push_edit(edit_t(line.position(), 0, L"a"), true);
-    line.push_edit(edit_t(line.position(), 0, L"b"), true);
-    line.push_edit(edit_t(line.position(), 0, L"c"), true);
-    line.push_edit(edit_t(line.position(), 0, L" "), true);
-    line.undo();
-    line.undo();
-    line.redo();
-    do_test(line.text() == L"abc");
-    // This removes the space insertion from the history, but does not coalesce with the first edit.
-    line.push_edit(edit_t(line.position(), 0, L"d"), true);
-    line.push_edit(edit_t(line.position(), 0, L"e"), true);
-    do_test(line.text() == L"abcde");
-    line.undo();
-    do_test(line.text() == L"abc");
-}
-
 // todo!("port this")
 static void test_new_parser_correctness() {
     say(L"Testing parser correctness");
@@ -2515,7 +2470,6 @@ static const test_t s_tests[]{
     {TEST_GROUP("word_motion"), test_word_motion},
     {TEST_GROUP("colors"), test_colors},
     {TEST_GROUP("input"), test_input},
-    {TEST_GROUP("undo"), test_undo},
     {TEST_GROUP("completion_insertions"), test_completion_insertions},
     {TEST_GROUP("illegal_command_exit_code"), test_illegal_command_exit_code},
     {TEST_GROUP("maybe"), test_maybe},
diff --git a/src/pager.cpp b/src/pager.cpp
index 23b068480..bf10f1076 100644
--- a/src/pager.cpp
+++ b/src/pager.cpp
@@ -16,6 +16,7 @@
 
 #include "common.h"
 #include "complete.h"
+#include "editable_line.rs.h"
 #include "fallback.h"
 #include "highlight.h"
 #include "maybe.h"
@@ -400,7 +401,7 @@ bool pager_t::completion_info_passes_filter(const comp_t &info) const {
     // If we have no filter, everything passes.
     if (!search_field_shown || this->search_field_line.empty()) return true;
 
-    const wcstring &needle = this->search_field_line.text();
+    const wcstring needle = *this->search_field_line.text();
 
     // Match against the description.
     if (string_fuzzy_match_string(needle, info.desc)) {
@@ -591,7 +592,7 @@ bool pager_t::completion_try_print(size_t cols, const wcstring &prefix, const co
     }
 
     // Add the search field.
-    wcstring search_field_text = search_field_line.text();
+    wcstring search_field_text = *search_field_line.text();
     // Append spaces to make it at least the required width.
     if (search_field_text.size() < PAGER_SEARCH_FIELD_WIDTH) {
         search_field_text.append(PAGER_SEARCH_FIELD_WIDTH - search_field_text.size(), L' ');
@@ -618,7 +619,7 @@ page_rendering_t pager_t::render() const {
     rendering.term_width = this->available_term_width;
     rendering.term_height = this->available_term_height;
     rendering.search_field_shown = this->search_field_shown;
-    rendering.search_field_line = this->search_field_line;
+    rendering.search_field_line = this->search_field_line.clone();
 
     for (size_t cols = PAGER_MAX_COLS; cols > 0; cols--) {
         // Initially empty rendering.
@@ -660,10 +661,10 @@ bool pager_t::rendering_needs_update(const page_rendering_t &rendering) const {
            rendering.term_width != this->available_term_width ||    //
            rendering.term_height != this->available_term_height ||  //
            rendering.selected_completion_idx !=
-               this->visual_selected_completion_index(rendering.rows, rendering.cols) ||    //
-           rendering.search_field_shown != this->search_field_shown ||                      //
-           rendering.search_field_line.text() != this->search_field_line.text() ||          //
-           rendering.search_field_line.position() != this->search_field_line.position() ||  //
+               this->visual_selected_completion_index(rendering.rows, rendering.cols) ||     //
+           rendering.search_field_shown != this->search_field_shown ||                       //
+           *rendering.search_field_line->text() != *this->search_field_line.text() ||        //
+           rendering.search_field_line->position() != this->search_field_line.position() ||  //
            (rendering.remaining_to_disclose > 0 && this->fully_disclosed);
 }
 
@@ -674,7 +675,7 @@ void pager_t::update_rendering(page_rendering_t *rendering) {
     }
 }
 
-pager_t::pager_t() = default;
+pager_t::pager_t() : search_field_line_box(new_editable_line()) {}
 pager_t::~pager_t() = default;
 
 bool pager_t::empty() const { return unfiltered_completion_infos.empty(); }
@@ -965,4 +966,5 @@ size_t pager_t::cursor_position() const {
     return result;
 }
 
-page_rendering_t::page_rendering_t() : screen_data(new_screen_data()) {}
+page_rendering_t::page_rendering_t()
+    : screen_data(new_screen_data()), search_field_line(new_editable_line()) {}
diff --git a/src/pager.h b/src/pager.h
index 4125f4d52..9087cec7e 100644
--- a/src/pager.h
+++ b/src/pager.h
@@ -34,7 +34,9 @@ class page_rendering_t {
     size_t remaining_to_disclose{0};
 
     bool search_field_shown{false};
-    editable_line_t search_field_line{};
+#if INCLUDE_RUST_HEADERS
+    rust::Box<editable_line_t> search_field_line;
+#endif
 
     // Returns a rendering with invalid data, useful to indicate "no rendering".
     page_rendering_t();
@@ -156,8 +158,11 @@ class pager_t {
                                           bool selected, page_rendering_t *rendering) const;
 
    public:
-    // The text of the search field.
-    editable_line_t search_field_line;
+// The text of the search field.
+#if INCLUDE_RUST_HEADERS
+    rust::Box<editable_line_t> search_field_line_box;
+    editable_line_t &search_field_line = *search_field_line_box;
+#endif
 
     // Extra text to display at the bottom of the pager.
     wcstring extra_progress_text{};
diff --git a/src/reader.cpp b/src/reader.cpp
index 508dae30e..fdd07cb63 100644
--- a/src/reader.cpp
+++ b/src/reader.cpp
@@ -210,183 +210,6 @@ static debounce_t &debounce_history_pager() {
     return *res;
 }
 
-bool edit_t::operator==(const edit_t &other) const {
-    return cursor_position_before_edit == other.cursor_position_before_edit &&
-           offset == other.offset && length == other.length && old == other.old &&
-           replacement == other.replacement;
-}
-
-void undo_history_t::clear() {
-    edits.clear();
-    edits_applied = 0;
-    may_coalesce = false;
-}
-
-void apply_edit(wcstring *target, std::vector<highlight_spec_t> *colors, const edit_t &edit) {
-    size_t offset = edit.offset;
-    target->replace(offset, edit.length, edit.replacement);
-
-    // Now do the same to highlighting.
-    auto it = colors->begin() + offset;
-    colors->erase(it, it + edit.length);
-    highlight_spec_t last_color = offset == 0 ? highlight_spec_t{} : colors->at(offset - 1);
-    colors->insert(it, edit.replacement.size(), last_color);
-}
-
-/// Returns the number of characters left of the cursor that are removed by the
-/// deletion in the given edit.
-static size_t chars_deleted_left_of_cursor(const edit_t &edit) {
-    if (edit.cursor_position_before_edit > edit.offset) {
-        return std::min(edit.length, edit.cursor_position_before_edit - edit.offset);
-    }
-    return 0;
-}
-
-/// Compute the position of the cursor after the given edit.
-static size_t cursor_position_after_edit(const edit_t &edit) {
-    size_t cursor = edit.cursor_position_before_edit + edit.replacement.size();
-    size_t removed = chars_deleted_left_of_cursor(edit);
-    return cursor > removed ? cursor - removed : 0;
-}
-
-void editable_line_t::set_colors(std::vector<highlight_spec_t> colors) {
-    assert(colors.size() == size());
-    colors_ = std::move(colors);
-}
-
-bool editable_line_t::undo() {
-    bool did_undo = false;
-    maybe_t<int> last_group_id{-1};
-    while (undo_history_.edits_applied != 0) {
-        const edit_t &edit = undo_history_.edits.at(undo_history_.edits_applied - 1);
-        if (did_undo && (!edit.group_id.has_value() || edit.group_id != last_group_id)) {
-            // We've restored all the edits in this logical undo group
-            break;
-        }
-        last_group_id = edit.group_id;
-        undo_history_.edits_applied--;
-        edit_t inverse = edit_t(edit.offset, edit.replacement.size(), L"");
-        inverse.replacement = edit.old;
-        size_t old_position = edit.cursor_position_before_edit;
-        apply_edit(&text_, &colors_, inverse);
-        set_position(old_position);
-        did_undo = true;
-    }
-
-    end_edit_group();
-    undo_history_.may_coalesce = false;
-    return did_undo;
-}
-
-void editable_line_t::clear() {
-    undo_history_.clear();
-    if (empty()) return;
-    apply_edit(&text_, &colors_, edit_t(0, text_.length(), L""));
-    set_position(0);
-}
-
-void editable_line_t::push_edit(edit_t edit, bool allow_coalesce) {
-    bool is_insertion = edit.length == 0;
-    /// Coalescing insertion does not create a new undo entry but adds to the last insertion.
-    if (allow_coalesce && is_insertion && want_to_coalesce_insertion_of(edit.replacement)) {
-        assert(edit.offset == position());
-        edit_t &last_edit = undo_history_.edits.back();
-        last_edit.replacement.append(edit.replacement);
-        apply_edit(&text_, &colors_, edit);
-        set_position(position() + edit.replacement.size());
-
-        assert(undo_history_.may_coalesce);
-        return;
-    }
-
-    // Assign a new group id or propagate the old one if we're in a logical grouping of edits
-    if (edit_group_level_ != -1) {
-        edit.group_id = edit_group_id_;
-    }
-
-    bool edit_does_nothing = edit.length == 0 && edit.replacement.empty();
-    if (edit_does_nothing) return;
-    if (undo_history_.edits_applied != undo_history_.edits.size()) {
-        // After undoing some edits, the user is making a new edit;
-        // we are about to create a new edit branch.
-        // Discard all edits that were undone because we only support
-        // linear undo/redo, they will be unreachable.
-        undo_history_.edits.erase(undo_history_.edits.begin() + undo_history_.edits_applied,
-                                  undo_history_.edits.end());
-    }
-    edit.cursor_position_before_edit = position();
-    edit.old = text_.substr(edit.offset, edit.length);
-    apply_edit(&text_, &colors_, edit);
-    set_position(cursor_position_after_edit(edit));
-    assert(undo_history_.edits_applied == undo_history_.edits.size());
-    undo_history_.may_coalesce =
-        is_insertion && (undo_history_.try_coalesce || edit.replacement.size() == 1);
-    undo_history_.edits_applied++;
-    undo_history_.edits.emplace_back(std::move(edit));
-}
-
-bool editable_line_t::redo() {
-    bool did_redo = false;
-
-    maybe_t<int> last_group_id{-1};
-    while (undo_history_.edits_applied < undo_history_.edits.size()) {
-        const edit_t &edit = undo_history_.edits.at(undo_history_.edits_applied);
-        if (did_redo && (!edit.group_id.has_value() || edit.group_id != last_group_id)) {
-            // We've restored all the edits in this logical undo group
-            break;
-        }
-        last_group_id = edit.group_id;
-        undo_history_.edits_applied++;
-        apply_edit(&text_, &colors_, edit);
-        set_position(cursor_position_after_edit(edit));
-        did_redo = true;
-    }
-
-    end_edit_group();
-    return did_redo;
-}
-
-void editable_line_t::begin_edit_group() {
-    if (++edit_group_level_ == 0) {
-        // Indicate that the next change must trigger the creation of a new history item
-        undo_history_.may_coalesce = false;
-        // Indicate that future changes should be coalesced into the same edit if possible.
-        undo_history_.try_coalesce = true;
-        // Assign a logical edit group id to future edits in this group
-        edit_group_id_ += 1;
-    }
-}
-
-void editable_line_t::end_edit_group() {
-    if (edit_group_level_ == -1) {
-        // Clamp the minimum value to -1 to prevent unbalanced end_edit_group() calls from breaking
-        // everything.
-        return;
-    }
-
-    if (--edit_group_level_ == -1) {
-        undo_history_.try_coalesce = false;
-        undo_history_.may_coalesce = false;
-    }
-}
-
-/// Whether we want to append this string to the previous edit.
-bool editable_line_t::want_to_coalesce_insertion_of(const wcstring &str) const {
-    // The previous edit must support coalescing.
-    if (!undo_history_.may_coalesce) return false;
-    // Only consolidate single character inserts.
-    if (str.size() != 1) return false;
-    // Make an undo group after every space.
-    if (str.at(0) == L' ' && !undo_history_.try_coalesce) return false;
-    assert(!undo_history_.edits.empty());
-    const edit_t &last_edit = undo_history_.edits.back();
-    // Don't add to the last edit if it deleted something.
-    if (last_edit.length != 0) return false;
-    // Must not have moved the cursor!
-    if (cursor_position_after_edit(last_edit) != position()) return false;
-    return true;
-}
-
 // Make the search case-insensitive unless we have an uppercase character.
 static history_search_flags_t smartcase_flags(const wcstring &query) {
     return query == wcstolower(query) ? history_search_ignore_case : 0;
@@ -714,7 +537,8 @@ class reader_data_t : public std::enable_shared_from_this<reader_data_t> {
     /// The parser being used.
     rust::Box<ParserRef> parser_ref;
     /// String containing the whole current commandline.
-    editable_line_t command_line;
+    rust::Box<editable_line_t> command_line_box;
+    editable_line_t &command_line;
     /// Whether the most recent modification to the command line was done by either history search
     /// or a pager selection change. When this is true and another transient change is made, the
     /// old transient change will be removed from the undo history.
@@ -859,6 +683,8 @@ class reader_data_t : public std::enable_shared_from_this<reader_data_t> {
     reader_data_t(rust::Box<ParserRef> parser, HistorySharedPtr &hist, reader_config_t &&conf)
         : conf(std::move(conf)),
           parser_ref(std::move(parser)),
+          command_line_box(new_editable_line()),
+          command_line(*command_line_box),
           screen(new_screen()),
           inputter(parser_ref->deref(), conf.in),
           history(hist.clone()) {}
@@ -872,7 +698,7 @@ class reader_data_t : public std::enable_shared_from_this<reader_data_t> {
     void erase_substring(editable_line_t *el, size_t offset, size_t length);
     /// Replace the text of length @length at @offset by @replacement.
     void replace_substring(editable_line_t *el, size_t offset, size_t length, wcstring replacement);
-    void push_edit(editable_line_t *el, edit_t edit);
+    void push_edit(editable_line_t *el, rust::Box<Edit> &&edit);
 
     /// Insert the character into the command line buffer and print it to the screen using syntax
     /// highlighting, etc.
@@ -1162,7 +988,7 @@ bool reader_data_t::is_repaint_needed(const std::vector<highlight_spec_t> *mcolo
     bool focused_on_pager = active_edit_line() == &pager.search_field_line;
     const layout_data_t &last = this->rendered_layout;
     return check(force_exec_prompt_and_repaint, L"forced") ||
-           check(command_line.text() != last.text, L"text") ||
+           check(*command_line.text() != last.text, L"text") ||
            check(mcolors && *mcolors != last.colors, L"highlight") ||
            check(selection != last.selection, L"selection") ||
            check(focused_on_pager != last.focused_on_pager, L"focus") ||
@@ -1179,8 +1005,10 @@ bool reader_data_t::is_repaint_needed(const std::vector<highlight_spec_t> *mcolo
 layout_data_t reader_data_t::make_layout_data() const {
     layout_data_t result{};
     bool focused_on_pager = active_edit_line() == &pager.search_field_line;
-    result.text = command_line.text();
-    result.colors = command_line.colors();
+    result.text = *command_line.text();
+    for (auto &color : editable_line_colors(command_line)) {
+        result.colors.push_back(color);
+    }
     assert(result.text.size() == result.colors.size());
     result.position = focused_on_pager ? pager.cursor_position() : command_line.position();
     result.selection = selection;
@@ -1200,10 +1028,10 @@ void reader_data_t::paint_layout(const wchar_t *reason) {
 
     wcstring full_line;
     if (conf.in_silent_mode) {
-        full_line = wcstring(cmd_line->text().length(), get_obfuscation_read_char());
+        full_line = wcstring(cmd_line->text()->length(), get_obfuscation_read_char());
     } else {
         // Combine the command and autosuggestion into one string.
-        full_line = combine_command_and_autosuggestion(cmd_line->text(), autosuggestion.text);
+        full_line = combine_command_and_autosuggestion(*cmd_line->text(), autosuggestion.text);
     }
 
     // Copy the colors and extend them with autosuggestion color.
@@ -1237,7 +1065,7 @@ void reader_data_t::paint_layout(const wchar_t *reason) {
 
     // Compute the indentation, then extend it with 0s for the autosuggestion. The autosuggestion
     // always conceptually has an indent of 0.
-    std::vector<int> indents = parse_util_compute_indents(cmd_line->text());
+    std::vector<int> indents = parse_util_compute_indents(*cmd_line->text());
     indents.resize(full_line.size(), 0);
 
     auto ffi_colors = new_highlight_spec_list();
@@ -1250,7 +1078,8 @@ void reader_data_t::paint_layout(const wchar_t *reason) {
 
 /// Internal helper function for handling killing parts of text.
 void reader_data_t::kill(editable_line_t *el, size_t begin_idx, size_t length, int mode, int newv) {
-    const wchar_t *begin = el->text().c_str() + begin_idx;
+    wcstring text = *el->text();
+    const wchar_t *begin = text.c_str() + begin_idx;
     if (newv) {
         kill_item = wcstring(begin, length);
         kill_add(kill_item);
@@ -1356,14 +1185,14 @@ void reader_data_t::fill_history_pager(history_pager_invocation_t why,
             old_pager_index = pager.selected_completion_index();
             break;
     }
-    const wcstring &search_term = pager.search_field_line.text();
+    const wcstring search_term = *pager.search_field_line.text();
     auto shared_this = this->shared_from_this();
     std::function<history_pager_result_t()> func = [=]() {
         return history_pager_search(**shared_this->history, direction, index, search_term);
     };
     std::function<void(const history_pager_result_t &)> completion =
         [=](const history_pager_result_t &result) {
-            if (search_term != shared_this->pager.search_field_line.text())
+            if (search_term != *shared_this->pager.search_field_line.text())
                 return;  // Stale request.
             if (result.matched_commands->empty() && why == history_pager_invocation_t::Advance) {
                 // No more matches, keep the existing ones and flash.
@@ -1412,7 +1241,7 @@ void reader_data_t::pager_selection_changed() {
     }
 
     // Only update if something changed, to avoid useless edits in the undo history.
-    if (new_cmd_line != command_line.text()) {
+    if (new_cmd_line != *command_line.text()) {
         set_buffer_maintaining_pager(new_cmd_line, cursor_pos, true /* transient */);
     }
 }
@@ -1548,8 +1377,9 @@ bool reader_data_t::expand_abbreviation_at_cursor(size_t cursor_backtrack) {
         this->update_commandline_state();
         size_t cursor_pos = el->position() - std::min(el->position(), cursor_backtrack);
         if (auto replacement =
-                reader_expand_abbreviation_at_cursor(el->text(), cursor_pos, this->parser())) {
-            push_edit(el, edit_t{replacement->range, *replacement->text});
+                reader_expand_abbreviation_at_cursor(*el->text(), cursor_pos, this->parser())) {
+            push_edit(el, new_edit(replacement->range.start, replacement->range.end(),
+                                   *replacement->text));
             if (replacement->has_cursor) {
                 update_buff_pos(el, replacement->cursor);
             } else {
@@ -1832,7 +1662,7 @@ void reader_data_t::delete_char(bool backward) {
     int width;
     do {
         pos--;
-        width = fish_wcwidth(el->text().at(pos));
+        width = fish_wcwidth(el->text()->at(pos));
     } while (width == 0 && pos > 0);
     erase_substring(el, pos, pos_end - pos);
     update_buff_pos(el);
@@ -1844,7 +1674,7 @@ void reader_data_t::delete_char(bool backward) {
 /// Returns true if the string changed.
 void reader_data_t::insert_string(editable_line_t *el, const wcstring &str) {
     if (!str.empty()) {
-        el->push_edit(edit_t(el->position(), 0, str),
+        el->push_edit(new_edit(el->position(), el->position(), str),
                       !history_search.active() /* allow_coalesce */);
     }
 
@@ -1855,18 +1685,18 @@ void reader_data_t::insert_string(editable_line_t *el, const wcstring &str) {
     maybe_refilter_pager(el);
 }
 
-void reader_data_t::push_edit(editable_line_t *el, edit_t edit) {
+void reader_data_t::push_edit(editable_line_t *el, rust::Box<Edit> &&edit) {
     el->push_edit(std::move(edit), false /* allow_coalesce */);
     maybe_refilter_pager(el);
 }
 
 void reader_data_t::erase_substring(editable_line_t *el, size_t offset, size_t length) {
-    push_edit(el, edit_t(offset, length, L""));
+    push_edit(el, new_edit(offset, offset + length, L""));
 }
 
 void reader_data_t::replace_substring(editable_line_t *el, size_t offset, size_t length,
                                       wcstring replacement) {
-    push_edit(el, edit_t(offset, length, std::move(replacement)));
+    push_edit(el, new_edit(offset, offset + length, std::move(replacement)));
 }
 
 /// Insert the string in the given command line at the given cursor position. The function checks if
@@ -2003,7 +1833,7 @@ void reader_data_t::completion_insert(const wcstring &val, size_t token_end,
     if (el->position() != token_end) update_buff_pos(el, token_end);
 
     size_t cursor = el->position();
-    wcstring new_command_line = completion_apply_to_command_line(val, flags, el->text(), &cursor,
+    wcstring new_command_line = completion_apply_to_command_line(val, flags, *el->text(), &cursor,
                                                                  false /* not append only */);
     set_buffer_maintaining_pager(new_command_line, cursor);
 }
@@ -2094,7 +1924,7 @@ bool reader_data_t::can_autosuggest() const {
     const editable_line_t *el = active_edit_line();
     const wchar_t *whitespace = L" \t\r\n\v";
     return conf.autosuggest_ok && !suppress_autosuggestion && history_search.is_at_end() &&
-           el == &command_line && el->text().find_first_not_of(whitespace) != wcstring::npos;
+           el == &command_line && el->text()->find_first_not_of(whitespace) != wcstring::npos;
 }
 
 // Called after an autosuggestion has been computed on a background thread.
@@ -2103,7 +1933,7 @@ void reader_data_t::autosuggest_completed(autosuggestion_t result) {
     if (result.search_string == in_flight_autosuggest_request) {
         in_flight_autosuggest_request.clear();
     }
-    if (result.search_string != command_line.text()) {
+    if (result.search_string != *command_line.text()) {
         // This autosuggestion is stale.
         return;
     }
@@ -2144,22 +1974,22 @@ void reader_data_t::update_autosuggestion() {
     // This is also the main mechanism by which readline commands that don't change the command line
     // text avoid recomputing the autosuggestion.
     const editable_line_t &el = command_line;
-    if (autosuggestion.text.size() > el.text().size() &&
+    if (autosuggestion.text.size() > el.text()->size() &&
         (autosuggestion.icase
-             ? string_prefixes_string_case_insensitive(el.text(), autosuggestion.text)
-             : string_prefixes_string(el.text(), autosuggestion.text))) {
+             ? string_prefixes_string_case_insensitive(*el.text(), autosuggestion.text)
+             : string_prefixes_string(*el.text(), autosuggestion.text))) {
         return;
     }
 
     // Do nothing if we've already kicked off this autosuggest request.
-    if (el.text() == in_flight_autosuggest_request) return;
-    in_flight_autosuggest_request = el.text();
+    if (*el.text() == in_flight_autosuggest_request) return;
+    in_flight_autosuggest_request = *el.text();
 
     // Clear the autosuggestion and kick it off in the background.
     FLOG(reader_render, L"Autosuggesting");
     autosuggestion.clear();
     std::function<autosuggestion_t()> performer =
-        get_autosuggestion_performer(parser(), el.text(), el.position(), **history);
+        get_autosuggestion_performer(parser(), *el.text(), el.position(), **history);
     auto shared_this = this->shared_from_this();
     std::function<void(autosuggestion_t)> completion = [shared_this](autosuggestion_t result) {
         shared_this->autosuggest_completed(std::move(result));
@@ -2311,7 +2141,7 @@ bool reader_data_t::handle_completions(const completion_list_t &comp, size_t tok
     bool success = false;
     const editable_line_t *el = &command_line;
 
-    const wcstring tok(el->text(), token_begin, token_end - token_begin);
+    const wcstring tok(*el->text(), token_begin, token_end - token_begin);
 
     // Check trivial cases.
     size_t size = comp.size();
@@ -2431,7 +2261,7 @@ bool reader_data_t::handle_completions(const completion_list_t &comp, size_t tok
             // a prefix; don't insert a space after it.
             if (prefix_is_partial_completion) flags |= COMPLETE_NO_SPACE;
             completion_insert(common_prefix, token_end, flags);
-            cycle_command_line = command_line.text();
+            cycle_command_line = *command_line.text();
             cycle_cursor_pos = command_line.position();
         }
     }
@@ -2665,7 +2495,7 @@ static void reader_interactive_destroy() {
 /// Set the specified string as the current buffer.
 void reader_data_t::set_command_line_and_position(editable_line_t *el, wcstring &&new_str,
                                                   size_t pos) {
-    push_edit(el, edit_t(0, el->size(), std::move(new_str)));
+    push_edit(el, new_edit(0, el->size(), std::move(new_str)));
     el->set_position(pos);
     update_buff_pos(el, pos);
 }
@@ -2685,7 +2515,8 @@ void reader_data_t::replace_current_token(wcstring &&new_token) {
 
     // Find current token.
     editable_line_t *el = active_edit_line();
-    const wchar_t *buff = el->text().c_str();
+    auto text = *el->text();
+    const wchar_t *buff = text.c_str();
     parse_util_token_extent(buff, el->position(), &begin, &end, nullptr, nullptr);
 
     if (!begin || !end) return;
@@ -2730,7 +2561,8 @@ void reader_data_t::move_word(editable_line_t *el, bool move_right, bool erase,
 
     // When moving left, a value of 1 means the character at index 0.
     auto state = new_move_word_state_machine(style);
-    const wchar_t *const command_line = el->text().c_str();
+    auto text = *el->text();
+    const wchar_t *const command_line = text.c_str();
     const size_t start_buff_pos = el->position();
 
     size_t buff_pos = el->position();
@@ -2851,10 +2683,14 @@ static parser_test_error_bits_t reader_shell_test(const parser_t &parser, const
 void reader_data_t::highlight_complete(highlight_result_t result) {
     ASSERT_IS_MAIN_THREAD();
     in_flight_highlight_request.clear();
-    if (result.text == command_line.text()) {
+    if (result.text == *command_line.text()) {
         assert(result.colors.size() == command_line.size());
         if (this->is_repaint_needed(&result.colors)) {
-            command_line.set_colors(std::move(result.colors));
+            auto ffi_colors = new_highlight_spec_list();
+            for (auto &c : result.colors) {
+                ffi_colors->push(c);
+            }
+            command_line.set_colors(*ffi_colors);
             this->layout_and_repaint(L"highlight");
         }
     }
@@ -2863,17 +2699,19 @@ void reader_data_t::highlight_complete(highlight_result_t result) {
 // Given text and  whether IO is allowed, return a function that performs highlighting. The function
 // may be invoked on a background thread.
 static std::function<highlight_result_t(void)> get_highlight_performer(const parser_t &parser,
-                                                                       const editable_line_t &el,
+                                                                       const editable_line_t *el,
                                                                        bool io_ok) {
     // shard_ptr to work around std::function requiring copyable types
     auto vars = std::make_shared<rust::Box<::EnvDyn>>(parser.vars().snapshot());
     uint32_t generation_count = read_generation_count();
+    size_t position = el->position();
+    wcstring text = *el->text();
     return [=]() -> highlight_result_t {
-        if (el.text().empty()) return {};
+        if (text.empty()) return {};
         auto ctx = get_bg_context(**vars, generation_count);
-        std::vector<highlight_spec_t> colors(el.text().size(), highlight_spec_t{});
-        highlight_shell(el.text(), colors, *ctx, io_ok, std::make_shared<size_t>(el.position()));
-        return highlight_result_t{std::move(colors), el.text()};
+        std::vector<highlight_spec_t> colors(text.size(), highlight_spec_t{});
+        highlight_shell(text, colors, *ctx, io_ok, std::make_shared<size_t>(position));
+        return highlight_result_t{std::move(colors), text};
     };
 }
 
@@ -2883,12 +2721,12 @@ void reader_data_t::super_highlight_me_plenty() {
 
     // Do nothing if this text is already in flight.
     const editable_line_t *el = &command_line;
-    if (el->text() == in_flight_highlight_request) return;
-    in_flight_highlight_request = el->text();
+    if (*el->text() == in_flight_highlight_request) return;
+    in_flight_highlight_request = *el->text();
 
     FLOG(reader_render, L"Highlighting");
     std::function<highlight_result_t()> highlight_performer =
-        get_highlight_performer(parser(), *el, true /* io_ok */);
+        get_highlight_performer(parser(), el, true /* io_ok */);
     auto shared_this = this->shared_from_this();
     std::function<void(highlight_result_t)> completion = [shared_this](highlight_result_t result) {
         shared_this->highlight_complete(std::move(result));
@@ -2908,8 +2746,8 @@ void reader_data_t::finish_highlighting_before_exec() {
         // 1: The user hit return after highlighting finished, so current highlighting is correct.
         // 2: The user hit return before highlighting started, so current highlighting is stale.
         // We can distinguish these based on what we last rendered.
-        current_highlight_ok = (this->rendered_layout.text == command_line.text());
-    } else if (in_flight_highlight_request == command_line.text()) {
+        current_highlight_ok = (this->rendered_layout.text == *command_line.text());
+    } else if (in_flight_highlight_request == *command_line.text()) {
         // The user hit return while our in-flight highlight request was still processing the text.
         // Wait for its completion to run, but not forever.
         namespace sc = std::chrono;
@@ -2933,7 +2771,7 @@ void reader_data_t::finish_highlighting_before_exec() {
     if (!current_highlight_ok) {
         // We need to do a quick highlight without I/O.
         auto highlight_no_io =
-            get_highlight_performer(parser(), command_line, false /* io not ok */);
+            get_highlight_performer(parser(), &command_line, false /* io not ok */);
         this->highlight_complete(highlight_no_io());
     }
 }
@@ -3124,7 +2962,7 @@ static bool selection_is_at_top(const reader_data_t *data) {
 
 void reader_data_t::update_commandline_state() const {
     auto snapshot = commandline_state_snapshot();
-    snapshot->text = this->command_line.text();
+    snapshot->text = *this->command_line.text();
     snapshot->cursor_pos = this->command_line.position();
     if (this->history) {
         snapshot->history = (*this->history)->clone();
@@ -3139,7 +2977,7 @@ void reader_data_t::update_commandline_state() const {
 void reader_data_t::apply_commandline_state_changes() {
     // Only the text and cursor position may be changed.
     commandline_state_t state = commandline_get_state();
-    if (state.text != this->command_line.text() ||
+    if (state.text != *this->command_line.text() ||
         state.cursor_pos != this->command_line.position()) {
         // The commandline builtin changed our contents.
         this->clear_pager();
@@ -3155,12 +2993,13 @@ void reader_data_t::compute_and_apply_completions(readline_cmd_t c, readline_loo
 
     // Remove a trailing backslash. This may trigger an extra repaint, but this is
     // rare.
-    if (is_backslashed(el->text(), el->position())) {
+    if (is_backslashed(*el->text(), el->position())) {
         delete_char();
     }
 
     // Get the string; we have to do this after removing any trailing backslash.
-    const wchar_t *const buff = el->text().c_str();
+    auto text = *el->text();
+    const wchar_t *const buff = text.c_str();
 
     // Figure out the extent of the command substitution surrounding the cursor.
     // This is because we only look at the current command substitution to form
@@ -3200,7 +3039,7 @@ void reader_data_t::compute_and_apply_completions(readline_cmd_t c, readline_loo
             rls.complete_did_insert = false;
             size_t tok_off = static_cast<size_t>(token_begin - buff);
             size_t tok_len = static_cast<size_t>(token_end - token_begin);
-            push_edit(el, edit_t{tok_off, tok_len, std::move(*wc_expanded)});
+            push_edit(el, new_edit(tok_off, tok_off + tok_len, std::move(*wc_expanded)));
             return;
     }
 
@@ -3217,14 +3056,14 @@ void reader_data_t::compute_and_apply_completions(readline_cmd_t c, readline_loo
 
     // User-supplied completions may have changed the commandline - prevent buffer
     // overflow.
-    if (token_begin > buff + el->text().size()) token_begin = buff + el->text().size();
-    if (token_end > buff + el->text().size()) token_end = buff + el->text().size();
+    if (token_begin > buff + el->text()->size()) token_begin = buff + el->text()->size();
+    if (token_end > buff + el->text()->size()) token_end = buff + el->text()->size();
 
     // Munge our completions.
     rls.comp->sort_and_prioritize(CompletionRequestOptions());
 
     // Record our cycle_command_line.
-    cycle_command_line = el->text();
+    cycle_command_line = *el->text();
     cycle_cursor_pos = token_end - buff;
 
     rls.complete_did_insert = handle_completions(*rls.comp, token_begin - buff, token_end - buff);
@@ -3470,7 +3309,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         // Go to beginning of line.
         case rl::beginning_of_line: {
             editable_line_t *el = active_edit_line();
-            while (el->position() > 0 && el->text().at(el->position() - 1) != L'\n') {
+            while (el->position() > 0 && el->text()->at(el->position() - 1) != L'\n') {
                 update_buff_pos(el, el->position() - 1);
             }
             break;
@@ -3478,7 +3317,8 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         case rl::end_of_line: {
             editable_line_t *el = active_edit_line();
             if (el->position() < el->size()) {
-                const wchar_t *buff = el->text().c_str();
+                auto text = *el->text();
+                const wchar_t *buff = text.c_str();
                 while (buff[el->position()] && buff[el->position()] != L'\n') {
                     update_buff_pos(el, el->position() + 1);
                 }
@@ -3611,7 +3451,8 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         }
         case rl::kill_line: {
             editable_line_t *el = active_edit_line();
-            const wchar_t *buff = el->text().c_str();
+            auto text = *el->text();
+            const wchar_t *buff = text.c_str();
             const wchar_t *begin = &buff[el->position()];
             const wchar_t *end = begin;
 
@@ -3630,7 +3471,8 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
             if (el->position() == 0) {
                 break;
             }
-            const wchar_t *buff = el->text().c_str();
+            auto text = *el->text();
+            const wchar_t *buff = text.c_str();
             const wchar_t *end = &buff[el->position()];
             const wchar_t *begin = end;
 
@@ -3652,7 +3494,8 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         case rl::kill_inner_line:  // Do not kill the following newline
         {
             editable_line_t *el = active_edit_line();
-            const wchar_t *buff = el->text().c_str();
+            auto text = *el->text();
+            const wchar_t *buff = text.c_str();
 
             // Back up to the character just past the previous newline, or go to the beginning
             // of the command line. Note that if the position is on a newline, visually this
@@ -3736,7 +3579,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         }
         case rl::execute: {
             if (!this->handle_execute(rls)) {
-                event_fire_generic(parser(), L"fish_posterror", {command_line.text()});
+                event_fire_generic(parser(), L"fish_posterror", {*command_line.text()});
                 screen->reset_abandoning_line(termsize_last().width);
             }
             break;
@@ -3763,7 +3606,8 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
                 if (mode == reader_history_search_t::token) {
                     // Searching by token.
                     const wchar_t *begin, *end;
-                    const wchar_t *buff = el->text().c_str();
+                    auto text = *el->text();
+                    const wchar_t *buff = text.c_str();
                     parse_util_token_extent(buff, el->position(), &begin, &end, nullptr, nullptr);
                     if (begin) {
                         wcstring token(begin, end);
@@ -3775,7 +3619,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
                     }
                 } else {
                     // Searching by line.
-                    history_search.reset_to_mode(el->text(), **history, mode, 0);
+                    history_search.reset_to_mode(*el->text(), **history, mode, 0);
 
                     // Skip the autosuggestion in the history unless it was truncated.
                     const wcstring &suggest = autosuggestion.text;
@@ -3815,7 +3659,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
             }
 
             // Record our cycle_command_line.
-            cycle_command_line = command_line.text();
+            cycle_command_line = *command_line.text();
             cycle_cursor_pos = command_line.position();
 
             this->history_pager_active = true;
@@ -3826,7 +3670,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
             pager.set_prefix(MB_CUR_MAX > 1 ? L"► " : L"> ", false /* highlight */);
             // Update the search field, which triggers the actual history search.
             if (!history_search.active() || history_search.search_string().empty()) {
-                insert_string(&pager.search_field_line, command_line.text());
+                insert_string(&pager.search_field_line, *command_line.text());
             } else {
                 // If we have an actual history search already going, reuse that term
                 // - this is if the user looks around a bit and decides to switch to the pager.
@@ -3989,7 +3833,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
             } else {
                 // Not navigating the pager contents.
                 editable_line_t *el = active_edit_line();
-                int line_old = parse_util_get_line_from_offset(el->text(), el->position());
+                int line_old = parse_util_get_line_from_offset(*el->text(), el->position());
                 int line_new;
 
                 if (c == rl::up_line)
@@ -3997,12 +3841,12 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
                 else
                     line_new = line_old + 1;
 
-                int line_count = parse_util_lineno(el->text(), el->size()) - 1;
+                int line_count = parse_util_lineno(*el->text(), el->size()) - 1;
 
                 if (line_new >= 0 && line_new <= line_count) {
-                    auto indents = parse_util_compute_indents(el->text());
-                    size_t base_pos_new = parse_util_get_offset_from_line(el->text(), line_new);
-                    size_t base_pos_old = parse_util_get_offset_from_line(el->text(), line_old);
+                    auto indents = parse_util_compute_indents(*el->text());
+                    size_t base_pos_new = parse_util_get_offset_from_line(*el->text(), line_new);
+                    size_t base_pos_old = parse_util_get_offset_from_line(*el->text(), line_old);
 
                     assert(base_pos_new != static_cast<size_t>(-1) &&
                            base_pos_old != static_cast<size_t>(-1));
@@ -4011,7 +3855,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
 
                     size_t line_offset_old = el->position() - base_pos_old;
                     size_t total_offset_new = parse_util_get_offset(
-                        el->text(), line_new, line_offset_old - 4 * (indent_new - indent_old));
+                        *el->text(), line_new, line_offset_old - 4 * (indent_new - indent_old));
                     update_buff_pos(el, total_offset_new);
                 }
             }
@@ -4043,7 +3887,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
             // Drag the character before the cursor forward over the character at the cursor,
             // moving the cursor forward as well.
             if (el->position() > 0) {
-                wcstring local_cmd = el->text();
+                wcstring local_cmd = *el->text();
                 std::swap(local_cmd.at(el->position()), local_cmd.at(el->position() - 1));
                 set_command_line_and_position(el, std::move(local_cmd), el->position() + 1);
             }
@@ -4052,7 +3896,8 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         case rl::transpose_words: {
             editable_line_t *el = active_edit_line();
             size_t len = el->size();
-            const wchar_t *buff = el->text().c_str();
+            auto text = *el->text();
+            const wchar_t *buff = text.c_str();
             const wchar_t *tok_begin, *tok_end, *prev_begin, *prev_end;
 
             // If we are not in a token, look for one ahead.
@@ -4095,7 +3940,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
 
             // Check that the cursor is on a character
             if (buff_pos < el->size()) {
-                wchar_t chr = el->text().at(buff_pos);
+                wchar_t chr = el->text()->at(buff_pos);
                 wcstring replacement;
 
                 // Toggle the case of the current character
@@ -4128,7 +3973,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
 
                 // Loop through the selected characters and toggle their case.
                 for (size_t pos = start; pos < start + len && pos < el->size(); pos++) {
-                    wchar_t chr = el->text().at(pos);
+                    wchar_t chr = el->text()->at(pos);
 
                     // Toggle the case of the current character.
                     bool make_uppercase = iswlower(chr);
@@ -4163,7 +4008,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
                       false);
             wcstring replacement;
             for (; pos < el->position(); pos++) {
-                wchar_t chr = el->text().at(pos);
+                wchar_t chr = el->text()->at(pos);
 
                 // We always change the case; this decides whether we go uppercase (true) or
                 // lowercase (false).
@@ -4221,7 +4066,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         }
         case rl::insert_line_over: {
             editable_line_t *el = active_edit_line();
-            while (el->position() > 0 && el->text().at(el->position() - 1) != L'\n') {
+            while (el->position() > 0 && el->text()->at(el->position() - 1) != L'\n') {
                 update_buff_pos(el, el->position() - 1);
             }
             insert_char(el, L'\n');
@@ -4231,7 +4076,8 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
         case rl::insert_line_under: {
             editable_line_t *el = active_edit_line();
             if (el->position() < el->size()) {
-                const wchar_t *buff = el->text().c_str();
+                auto text = *el->text();
+                const wchar_t *buff = text.c_str();
                 while (buff[el->position()] && buff[el->position()] != L'\n') {
                     update_buff_pos(el, el->position() + 1);
                 }
@@ -4364,7 +4210,7 @@ void reader_data_t::add_to_history() {
     }
 
     // Historical behavior is to trim trailing spaces, unless escape (#7661).
-    wcstring text = command_line.text();
+    wcstring text = *command_line.text();
     while (!text.empty() && text.back() == L' ' &&
            count_preceding_backslashes(text, text.size() - 1) % 2 == 0) {
         text.pop_back();
@@ -4398,7 +4244,7 @@ parser_test_error_bits_t reader_data_t::expand_for_execute() {
     // Syntax check before expanding abbreviations. We could consider relaxing this: a string may be
     // syntactically invalid but become valid after expanding abbreviations.
     if (conf.syntax_check_ok) {
-        test_res = reader_shell_test(parser(), el->text());
+        test_res = reader_shell_test(parser(), *el->text());
         if (test_res & PARSER_TEST_ERROR) return test_res;
     }
 
@@ -4408,7 +4254,7 @@ parser_test_error_bits_t reader_data_t::expand_for_execute() {
         // Trigger syntax highlighting as we are likely about to execute this command.
         this->super_highlight_me_plenty();
         if (conf.syntax_check_ok) {
-            test_res = reader_shell_test(parser(), el->text());
+            test_res = reader_shell_test(parser(), *el->text());
         }
     }
     return test_res;
@@ -4422,7 +4268,7 @@ bool reader_data_t::handle_execute(readline_loop_state_t &rls) {
         if (this->history_pager_active &&
             this->pager.selected_completion_index() == PAGER_SELECTION_NONE) {
             command_line.push_edit(
-                edit_t{0, command_line.size(), this->pager.search_field_line.text()},
+                new_edit(0, command_line.size(), *this->pager.search_field_line.text()),
                 /* allow_coalesce */ false);
             command_line.set_position(this->pager.search_field_line.position());
         }
@@ -4445,13 +4291,14 @@ bool reader_data_t::handle_execute(readline_loop_state_t &rls) {
     if (el->position() >= el->size()) {
         // We're at the end of the text and not in a comment (issue #1225).
         continue_on_next_line =
-            is_backslashed(el->text(), el->position()) && !text_ends_in_comment(el->text());
+            is_backslashed(*el->text(), el->position()) && !text_ends_in_comment(*el->text());
     } else {
         // Allow mid line split if the following character is whitespace (issue #613).
-        if (is_backslashed(el->text(), el->position()) && iswspace(el->text().at(el->position()))) {
+        if (is_backslashed(*el->text(), el->position()) &&
+            iswspace(el->text()->at(el->position()))) {
             continue_on_next_line = true;
             // Check if the end of the line is backslashed (issue #4467).
-        } else if (is_backslashed(el->text(), el->size()) && !text_ends_in_comment(el->text())) {
+        } else if (is_backslashed(*el->text(), el->size()) && !text_ends_in_comment(*el->text())) {
             // Move the cursor to the end of the line.
             el->set_position(el->size());
             continue_on_next_line = true;
@@ -4708,7 +4555,7 @@ bool reader_data_t::jump(jump_direction_t dir, jump_precision_t precision, edita
             size_t tmp_pos = el->position();
 
             while (tmp_pos--) {
-                if (el->at(tmp_pos) == target) {
+                if ((wchar_t)el->at(tmp_pos) == target) {
                     if (precision == jump_precision_t::till) {
                         tmp_pos = std::min(el->size() - 1, tmp_pos + 1);
                     }
@@ -4721,7 +4568,7 @@ bool reader_data_t::jump(jump_direction_t dir, jump_precision_t precision, edita
         }
         case jump_direction_t::forward: {
             for (size_t tmp_pos = el->position() + 1; tmp_pos < el->size(); tmp_pos++) {
-                if (el->at(tmp_pos) == target) {
+                if ((wchar_t)el->at(tmp_pos) == target) {
                     if (precision == jump_precision_t::till && tmp_pos) {
                         tmp_pos--;
                     }
diff --git a/src/reader.h b/src/reader.h
index 29b73312b..434c9f9ef 100644
--- a/src/reader.h
+++ b/src/reader.h
@@ -25,117 +25,7 @@
 #include "reader.rs.h"
 #endif
 
-/// An edit action that can be undone.
-struct edit_t {
-    /// When undoing the edit we use this to restore the previous cursor position.
-    size_t cursor_position_before_edit = 0;
-
-    /// The span of text that is replaced by this edit.
-    size_t offset, length;
-
-    /// The strings that are removed and added by this edit, respectively.
-    wcstring old, replacement;
-
-    /// edit_t is only for contiguous changes, so to restore a group of arbitrary changes to the
-    /// command line we need to have a group id as forcibly coalescing changes is not enough.
-    maybe_t<int> group_id;
-
-    explicit edit_t(size_t offset, size_t length, wcstring replacement)
-        : offset(offset), length(length), replacement(std::move(replacement)) {}
-
-    explicit edit_t(source_range_t range, wcstring replacement)
-        : edit_t(range.start, range.length, std::move(replacement)) {}
-
-    /// Used for testing.
-    bool operator==(const edit_t &other) const;
-};
-
-/// Modify a string and its syntax highlighting according to the given edit.
-/// Currently exposed for testing only.
-void apply_edit(wcstring *target, std::vector<highlight_spec_t> *colors, const edit_t &edit);
-
-/// The history of all edits to some command line.
-struct undo_history_t {
-    /// The stack of edits that can be undone or redone atomically.
-    std::vector<edit_t> edits;
-
-    /// The position in the undo stack that corresponds to the current
-    /// state of the input line.
-    /// Invariants:
-    ///     edits_applied - 1 is the index of the next edit to undo.
-    ///     edits_applied     is the index of the next edit to redo.
-    ///
-    /// For example, if nothing was undone, edits_applied is edits.size().
-    /// If every single edit was undone, edits_applied is 0.
-    size_t edits_applied = 0;
-
-    /// Whether we allow the next edit to be grouped together with the
-    /// last one.
-    bool may_coalesce = false;
-
-    /// Whether to be more aggressive in coalescing edits. Ideally, it would be "force coalesce"
-    /// with guaranteed atomicity but as `edit_t` is strictly for contiguous changes, that guarantee
-    /// can't be made at this time.
-    bool try_coalesce = false;
-
-    /// Empty the history.
-    void clear();
-};
-
-/// Helper class for storing a command line.
-class editable_line_t {
-   public:
-    const wcstring &text() const { return text_; }
-
-    const std::vector<highlight_spec_t> &colors() const { return colors_; }
-    void set_colors(std::vector<highlight_spec_t> colors);
-
-    size_t position() const { return position_; }
-    void set_position(size_t position) { position_ = position; }
-
-    // Gets the length of the text.
-    size_t size() const { return text().size(); }
-
-    bool empty() const { return text().empty(); }
-
-    wchar_t at(size_t idx) const { return text().at(idx); }
-
-    void clear();
-
-    /// Modify the commandline according to @edit. Most modifications to the
-    /// text should pass through this function.
-    void push_edit(edit_t edit, bool allow_coalesce);
-
-    /// Undo the most recent edit that was not yet undone. Returns true on success.
-    bool undo();
-
-    /// Redo the most recent undo. Returns true on success.
-    bool redo();
-
-    /// Start a logical grouping of command line edits that should be undone/redone together.
-    void begin_edit_group();
-    /// End a logical grouping of command line edits that should be undone/redone together.
-    void end_edit_group();
-
-   private:
-    /// Whether we want to append this string to the previous edit.
-    bool want_to_coalesce_insertion_of(const wcstring &str) const;
-
-    /// The command line.
-    wcstring text_;
-    /// Syntax highlighting.
-    std::vector<highlight_spec_t> colors_;
-    /// The current position of the cursor in the command line.
-    size_t position_ = 0;
-
-    /// The history of all edits.
-    undo_history_t undo_history_;
-    /// The nesting level for atomic edits, so that recursive invocations of start_edit_group()
-    /// are not ended by one end_edit_group() call.
-    int32_t edit_group_level_ = -1;
-    /// Monotonically increasing edit group, ignored when edit_group_level_ is -1. Allowed to wrap.
-    uint32_t edit_group_id_ = -1;
-};
+#include "editable_line.h"
 
 int reader_read_ffi(const void *parser, int fd, const void *io_chain);
 /// Read commands from \c fd until encountering EOF.