shrink_selection without history selects first contained child

This changes the behavior of `shrink_history` to iterate through
child nodes until it finds one that is strictly contained within the
selection, i.e. exclusively. This produces more intuitive behavior for
selecting the "first logical thing" inside the selection.

helix-core/src/movement.rs

@@ -549,6 +549,25 @@ pub fn goto_treesitter_object(
     last_range
 }
 
+/// Finds the first child node under the given input node that is fully
+/// contained (i.e. strictly inside, non-inclusive) within the given range.
+pub fn find_first_contained_child<'n>(
+    mut node: Node<'n>,
+    range: &Range,
+    text: RopeSlice,
+) -> Option<Node<'n>> {
+    let start = text.char_to_byte(range.from());
+    let end = text.char_to_byte(range.to());
+    let mut cursor = node.walk();
+    let mut children = node.children(&mut cursor);
+
+    while node.start_byte() <= start || node.end_byte() >= end {
+        node = children.next()?;
+    }
+
+    Some(node)
+}
+
 #[cfg(test)]
 mod test {
     use ropey::Rope;

helix-core/src/object.rs

@@ -11,8 +11,9 @@ pub fn expand_selection(syntax: &Syntax, text: RopeSlice, selection: Selection)
 }
 
 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))
+    select_node_impl(syntax, text, selection, |descendant, from, to| {
+        let range = Range::new(from, to);
+        crate::movement::find_first_contained_child(descendant, &range, text).or(Some(descendant))
     })
 }
 

helix-term/tests/test/commands/movement.rs

@@ -89,18 +89,36 @@ async fn expand_shrink_selection() -> anyhow::Result<()> {
         ),
         // shrink with no expansion history defaults to first child
         (
+            helpers::platform_line(indoc! {r##"
+                #[(
+                    Some(thing),
+                    Some(other_thing),
+                )|]#
+            "##}),
+            "<A-i>",
             helpers::platform_line(indoc! {r##"
                 (
                     #[Some(thing)|]#,
                     Some(other_thing),
                 )
             "##}),
-            "<A-i>",
+        ),
+        // any movement cancels selection history and falls back to first child
+        (
             helpers::platform_line(indoc! {r##"
                 (
-                    #[Some|]#(thing),
+                    Some(#[thing|]#),
+                    Some(#(other_thing|)#),
+                )
+
+            "##}),
+            "<A-o><A-o><A-o>jkvkkk<A-i>",
+            helpers::platform_line(indoc! {r##"
+                (
+                    #[|Some(thing)]#,
                     Some(other_thing),
                 )
+
             "##}),
         ),
     ];