Implement a Component command for closing a buffer picker buffer

This is a basic example of a remappable command specific to a single
Component. It could be remapped like so:

    ```toml
    [keys.buffer-picker]
    C-d = "close_buffer_in_buffer_picker"
    ```

This has some rough edges:

* Can we namespace the commands so they don't all have to be very long
  and specific about which component they work for?
* How can we make this work for generics?
    * We can't define commands that operate on a `Picker<_>` for
      example. This example only works because we're using a
      `Picker<BufferMeta>`.
    * For Pickers and Menus we could use a `Vec<Box<dyn Item>>` and drop
      the generics but that would lose static dispatch.
    * Could we separate the part that needs generics into a different
      struct and have the functions operate on that?

helix-term/src/commands.rs

@@ -50,7 +50,7 @@ use movement::Movement;
 
 use crate::{
     args,
-    compositor::{self, Component, Compositor},
+    compositor::{self, Component, Compositor, EventResult},
     filter_picker_entry,
     job::Callback,
     keymap::{Keymaps, ReverseKeymap},
@@ -172,6 +172,11 @@ pub enum MappableCommand {
         fun: fn(cx: &mut Context),
         doc: &'static str,
     },
+    Component {
+        name: &'static str,
+        fun: fn(&mut dyn crate::compositor::Component, &mut compositor::Context) -> EventResult,
+        doc: &'static str,
+    },
 }
 
 macro_rules! static_commands {
@@ -209,6 +214,7 @@ impl MappableCommand {
                 }
             }
             Self::Static { fun, .. } => (fun)(cx),
+            Self::Component { .. } => unimplemented!(),
         }
     }
 
@@ -216,6 +222,7 @@ impl MappableCommand {
         match &self {
             Self::Typable { name, .. } => name,
             Self::Static { name, .. } => name,
+            Self::Component { .. } => unimplemented!(),
         }
     }
 
@@ -223,9 +230,18 @@ impl MappableCommand {
         match &self {
             Self::Typable { doc, .. } => doc,
             Self::Static { doc, .. } => doc,
+            Self::Component { .. } => unimplemented!(),
         }
     }
 
+    // TODO: macro for this...
+    #[allow(non_upper_case_globals)]
+    pub const close_buffer_in_buffer_picker: Self = Self::Component {
+        name: "close_buffer_in_buffer_picker",
+        fun: crate::ui::picker::close_buffer_in_buffer_picker,
+        doc: "Closes the currently focused buffer",
+    };
+
     #[rustfmt::skip]
     static_commands!(
         no_op, "Do nothing",
@@ -503,6 +519,7 @@ impl fmt::Debug for MappableCommand {
                 .field(name)
                 .field(args)
                 .finish(),
+            Self::Component { .. } => unimplemented!(),
         }
     }
 }
@@ -2526,17 +2543,19 @@ fn file_picker_in_current_directory(cx: &mut Context) {
     cx.push_layer(Box::new(overlaid(picker)));
 }
 
+pub struct BufferMeta {
+    pub id: DocumentId,
+    path: Option<PathBuf>,
+    is_modified: bool,
+    is_current: bool,
+    focused_at: std::time::Instant,
+}
+
+pub type BufferPicker = Picker<BufferMeta>;
+
 fn buffer_picker(cx: &mut Context) {
     let current = view!(cx.editor).doc;
 
-    struct BufferMeta {
-        id: DocumentId,
-        path: Option<PathBuf>,
-        is_modified: bool,
-        is_current: bool,
-        focused_at: std::time::Instant,
-    }
-
     impl ui::menu::Item for BufferMeta {
         type Data = ();
 
@@ -2710,6 +2729,7 @@ impl ui::menu::Item for MappableCommand {
                 Some(bindings) => format!("{} ({}) [{}]", doc, fmt_binding(bindings), name).into(),
                 None => format!("{} [{}]", doc, name).into(),
             },
+            MappableCommand::Component { .. } => unimplemented!(),
         }
     }
 }

helix-term/src/keymap/default.rs

@@ -379,9 +379,15 @@ pub fn default() -> HashMap<Domain, KeyTrie> {
         "home" => goto_line_start,
         "end" => goto_line_end_newline,
     });
+
+    let buffer_picker = keymap!({ "Buffer picker"
+        "C-x" => close_buffer_in_buffer_picker,
+    });
+
     hashmap!(
         Domain::Mode(Mode::Normal) => normal,
         Domain::Mode(Mode::Select) => select,
         Domain::Mode(Mode::Insert) => insert,
+        Domain::Component("buffer-picker") => buffer_picker,
     )
 }

helix-term/src/ui/picker.rs

@@ -802,6 +802,18 @@ impl<T: Item + 'static> Component for Picker<T> {
             _ => return EventResult::Ignored(None),
         };
 
+        match ctx.keymaps.get_by_component_id(self.id, key_event) {
+            crate::keymap::KeymapResult::Matched(crate::keymap::MappableCommand::Component {
+                fun,
+                ..
+            }) => {
+                if let EventResult::Consumed(callback) = fun(self, ctx) {
+                    return EventResult::Consumed(callback);
+                }
+            }
+            _ => (),
+        }
+
         let close_fn =
             EventResult::Consumed(Some(Box::new(|compositor: &mut Compositor, _ctx| {
                 // remove the layer
@@ -987,3 +999,39 @@ impl<T: Item + Send + 'static> Component for DynamicPicker<T> {
         Some(DYNAMIC_PICKER_ID)
     }
 }
+
+pub fn close_buffer_in_buffer_picker(
+    component: &mut dyn Component,
+    cx: &mut compositor::Context,
+) -> EventResult {
+    let Some(picker) = component
+        .as_any_mut()
+        .downcast_mut::<crate::commands::BufferPicker>()
+    else {
+        return EventResult::Ignored(None);
+    };
+    let Some(id) = picker.selection().map(|meta| meta.id) else {
+        return EventResult::Ignored(None);
+    };
+    match cx.editor.close_document(id, false) {
+        Ok(_) => {
+            picker.options.retain(|item| item.id != id);
+            if picker.options.is_empty() {
+                return close_fn();
+            }
+            picker.cursor = picker.cursor.saturating_sub(1);
+            picker.force_score();
+        }
+        // TODO: impl From<CloseError> for anyhow::Error
+        Err(_err) => cx.editor.set_error("Failed to close buffer"),
+    }
+
+    EventResult::Consumed(None)
+}
+
+fn close_fn() -> EventResult {
+    EventResult::Consumed(Some(Box::new(|compositor: &mut Compositor, _ctx| {
+        // remove the layer
+        compositor.last_picker = compositor.pop();
+    })))
+}