feat(commands): shrink_selection (#1340)

* feat(commands): shrink_selection

Add `shrink_selection` command that can be used to shrink
previously expanded selection.

To make `shrink_selection` work it was necessary to add
selection history to the Document since we want to shrink
the selection towards the syntax tree node that was initially
selected.

Selection history is cleared any time the user changes
selection other way than by `expand_selection`. This ensures
that we don't get some funky edge cases when user calls
`shrink_selection`.

Related: https://github.com/helix-editor/helix/discussions/1328

* Refactor shrink_selection, move history to view

* Remove useless comment

* Add default key mapping for extend&shrink selection

* Rework contains_selection method

* Shrink selection without expand selects first child

1 files changed, 3 insertions, 0 deletions

diff --git a/helix-view/src/view.rs b/helix-view/src/view.rs
index 94d67acd..89a6c196 100644
--- a/helix-view/src/view.rs
+++ b/helix-view/src/view.rs
@@ -80,6 +80,8 @@ pub struct View {
     // uses two docs because we want to be able to swap between the
     // two last modified docs which we need to manually keep track of
     pub last_modified_docs: [Option<DocumentId>; 2],
+    /// used to store previous selections of tree-sitter objecs
+    pub object_selections: Vec<Selection>,
 }
 
 impl View {
@@ -92,6 +94,7 @@ impl View {
             jumps: JumpList::new((doc, Selection::point(0))), // TODO: use actual sel
             last_accessed_doc: None,
             last_modified_docs: [None, None],
+            object_selections: Vec::new(),
         }
     }