add select_next_sibling and select_prev_sibling commands (#1495)

* add select_next_sibling and select_prev_sibling commands

* refactor objects to use higher order functions

* address clippy feedback

* move selection cloning into commands

* add default keybindings under left/right brackets

* use [+t,]+t for selecting sibling syntax nodes

* setup Alt-{j,k,h,l} default keymaps for syntax selection commands

* reduce boilerplate of select_next/prev_sibling in commands

* import tree-sitter Node type in commands

4 files changed, 94 insertions, 43 deletions

diff --git a/book/src/keymap.md b/book/src/keymap.md
index ea890575..905ec48f 100644
--- a/book/src/keymap.md
+++ b/book/src/keymap.md
@@ -119,6 +119,10 @@
 | `Alt-K`  | Remove selections matching the regex                              | `remove_selections`                  |
 | `$`      | Pipe each selection into shell command, keep selections where command returned 0 | `shell_keep_pipe`     |
 | `Ctrl-c` | Comment/uncomment the selections                                  | `toggle_comments`                    |
+| `Alt-k`  | Expand selection to parent syntax node                            | `expand_selection`                   |
+| `Alt-j`  | Shrink syntax tree object selection                               | `shrink_selection`                   |
+| `Alt-h`  | Select previous sibling node in syntax tree                       | `select_prev_sibling`                |
+| `Alt-l`  | Select next sibling node in syntax tree                           | `select_next_sibling`                |
 
 ### Search
 
@@ -262,8 +266,6 @@ Mappings in the style of [vim-unimpaired](https://github.com/tpope/vim-unimpaire
 | `]D`     | Go to last diagnostic in document (**LSP**)  | `goto_last_diag`    |
 | `[space` | Add newline above                            | `add_newline_above` |
 | `]space` | Add newline below                            | `add_newline_below` |
-| `]o`     | Expand syntax tree object selection.         | `expand_selection`  |
-| `[o`     | Shrink syntax tree object selection.         | `shrink_selection`  |
 
 ## Insert Mode
 
diff --git a/helix-core/src/object.rs b/helix-core/src/object.rs
index 3363e20b..b06f4144 100644
--- a/helix-core/src/object.rs
+++ b/helix-core/src/object.rs
@@ -1,56 +1,72 @@
 use crate::{Range, RopeSlice, Selection, Syntax};
+use tree_sitter::Node;
 
-pub fn expand_selection(syntax: &Syntax, text: RopeSlice, selection: &Selection) -> Selection {
-    let tree = syntax.tree();
-
-    selection.clone().transform(|range| {
-        let from = text.char_to_byte(range.from());
-        let to = text.char_to_byte(range.to());
+pub fn expand_selection(syntax: &Syntax, text: RopeSlice, selection: Selection) -> Selection {
+    select_node_impl(syntax, text, selection, |descendant, from, to| {
+        if descendant.start_byte() == from && descendant.end_byte() == to {
+            descendant.parent()
+        } else {
+            Some(descendant)
+        }
+    })
+}
 
-        // find parent of a descendant that matches the range
-        let parent = match tree
-            .root_node()
-            .descendant_for_byte_range(from, to)
-            .and_then(|node| {
-                if node.start_byte() == from && node.end_byte() == to {
-                    node.parent()
-                } else {
-                    Some(node)
-                }
-            }) {
-            Some(parent) => parent,
-            None => return range,
-        };
+pub fn shrink_selection(syntax: &Syntax, text: RopeSlice, selection: Selection) -> Selection {
+    select_node_impl(syntax, text, selection, |descendant, _from, _to| {
+        descendant.child(0).or(Some(descendant))
+    })
+}
 
-        let from = text.byte_to_char(parent.start_byte());
-        let to = text.byte_to_char(parent.end_byte());
+pub fn select_sibling<F>(
+    syntax: &Syntax,
+    text: RopeSlice,
+    selection: Selection,
+    sibling_fn: &F,
+) -> Selection
+where
+    F: Fn(Node) -> Option<Node>,
+{
+    select_node_impl(syntax, text, selection, |descendant, _from, _to| {
+        find_sibling_recursive(descendant, sibling_fn)
+    })
+}
 
-        if range.head < range.anchor {
-            Range::new(to, from)
-        } else {
-            Range::new(from, to)
-        }
+fn find_sibling_recursive<F>(node: Node, sibling_fn: F) -> Option<Node>
+where
+    F: Fn(Node) -> Option<Node>,
+{
+    sibling_fn(node).or_else(|| {
+        node.parent()
+            .and_then(|node| find_sibling_recursive(node, sibling_fn))
     })
 }
 
-pub fn shrink_selection(syntax: &Syntax, text: RopeSlice, selection: &Selection) -> Selection {
+fn select_node_impl<F>(
+    syntax: &Syntax,
+    text: RopeSlice,
+    selection: Selection,
+    select_fn: F,
+) -> Selection
+where
+    F: Fn(Node, usize, usize) -> Option<Node>,
+{
     let tree = syntax.tree();
 
-    selection.clone().transform(|range| {
+    selection.transform(|range| {
         let from = text.char_to_byte(range.from());
         let to = text.char_to_byte(range.to());
 
-        let descendant = match tree.root_node().descendant_for_byte_range(from, to) {
-            // find first child, if not possible, fallback to the node that contains selection
-            Some(descendant) => match descendant.child(0) {
-                Some(child) => child,
-                None => descendant,
-            },
+        let node = match tree
+            .root_node()
+            .descendant_for_byte_range(from, to)
+            .and_then(|node| select_fn(node, from, to))
+        {
+            Some(node) => node,
             None => return range,
         };
 
-        let from = text.byte_to_char(descendant.start_byte());
-        let to = text.byte_to_char(descendant.end_byte());
+        let from = text.byte_to_char(node.start_byte());
+        let to = text.byte_to_char(node.end_byte());
 
         if range.head < range.anchor {
             Range::new(to, from)
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 9ac12931..de4bfa49 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -11,6 +11,7 @@ use helix_core::{
     object, pos_at_coords,
     regex::{self, Regex, RegexBuilder},
     search, selection, shellwords, surround, textobject,
+    tree_sitter::Node,
     unicode::width::UnicodeWidthChar,
     LineEnding, Position, Range, Rope, RopeGraphemes, RopeSlice, Selection, SmallVec, Tendril,
     Transaction,
@@ -363,6 +364,8 @@ impl MappableCommand {
         rotate_selection_contents_backward, "Rotate selections contents backward",
         expand_selection, "Expand selection to parent syntax node",
         shrink_selection, "Shrink selection to previously expanded syntax node",
+        select_next_sibling, "Select the next sibling in the syntax tree",
+        select_prev_sibling, "Select the previous sibling in the syntax tree",
         jump_forward, "Jump forward on jumplist",
         jump_backward, "Jump backward on jumplist",
         save_selection, "Save the current selection to the jumplist",
@@ -5502,7 +5505,7 @@ fn expand_selection(cx: &mut Context) {
             // save current selection so it can be restored using shrink_selection
             view.object_selections.push(current_selection.clone());
 
-            let selection = object::expand_selection(syntax, text, current_selection);
+            let selection = object::expand_selection(syntax, text, current_selection.clone());
             doc.set_selection(view.id, selection);
         }
     };
@@ -5528,7 +5531,7 @@ fn shrink_selection(cx: &mut Context) {
         // if not previous selection, shrink to first child
         if let Some(syntax) = doc.syntax() {
             let text = doc.text().slice(..);
-            let selection = object::shrink_selection(syntax, text, current_selection);
+            let selection = object::shrink_selection(syntax, text, current_selection.clone());
             doc.set_selection(view.id, selection);
         }
     };
@@ -5536,6 +5539,33 @@ fn shrink_selection(cx: &mut Context) {
     cx.editor.last_motion = Some(Motion(Box::new(motion)));
 }
 
+fn select_sibling_impl<F>(cx: &mut Context, sibling_fn: &'static F)
+where
+    F: Fn(Node) -> Option<Node>,
+{
+    let motion = |editor: &mut Editor| {
+        let (view, doc) = current!(editor);
+
+        if let Some(syntax) = doc.syntax() {
+            let text = doc.text().slice(..);
+            let current_selection = doc.selection(view.id);
+            let selection =
+                object::select_sibling(syntax, text, current_selection.clone(), sibling_fn);
+            doc.set_selection(view.id, selection);
+        }
+    };
+    motion(cx.editor);
+    cx.editor.last_motion = Some(Motion(Box::new(motion)));
+}
+
+fn select_next_sibling(cx: &mut Context) {
+    select_sibling_impl(cx, &|node| Node::next_sibling(&node))
+}
+
+fn select_prev_sibling(cx: &mut Context) {
+    select_sibling_impl(cx, &|node| Node::prev_sibling(&node))
+}
+
 fn match_brackets(cx: &mut Context) {
     let (view, doc) = current!(cx.editor);
 
diff --git a/helix-term/src/keymap.rs b/helix-term/src/keymap.rs
index 79a06206..e5990d72 100644
--- a/helix-term/src/keymap.rs
+++ b/helix-term/src/keymap.rs
@@ -552,6 +552,11 @@ impl Default for Keymaps {
             "S" => split_selection,
             ";" => collapse_selection,
             "A-;" => flip_selections,
+            "A-k" => expand_selection,
+            "A-j" => shrink_selection,
+            "A-h" => select_prev_sibling,
+            "A-l" => select_next_sibling,
+
             "%" => select_all,
             "x" => extend_line,
             "X" => extend_to_line_bounds,
@@ -569,13 +574,11 @@ impl Default for Keymaps {
                 "d" => goto_prev_diag,
                 "D" => goto_first_diag,
                 "space" => add_newline_above,
-                "o" => shrink_selection,
             },
             "]" => { "Right bracket"
                 "d" => goto_next_diag,
                 "D" => goto_last_diag,
                 "space" => add_newline_below,
-                "o" => expand_selection,
             },
 
             "/" => search,