Registers: Reverse first/last and rename to latest/oldest

The `first`/`last` names exposed some internal implementation details
that changed in the parent commit. The `latest`/`oldest` functions
return the same as `first`/`last` before the parent commit and now have
their names switched to focus on what they return about the register
rather than internal register ordering details.

helix-term/src/commands.rs

@@ -2125,7 +2125,7 @@ fn search_next_or_prev_impl(cx: &mut Context, movement: Movement, direction: Dir
         .unwrap_or(cx.editor.registers.last_search_register);
     let config = cx.editor.config();
     let scrolloff = config.scrolloff;
-    if let Some(query) = cx.editor.registers.first(register, cx.editor) {
+    if let Some(query) = cx.editor.registers.latest(register, cx.editor) {
         let search_config = &config.search;
         let case_insensitive = if search_config.smart_case {
             !query.chars().any(char::is_uppercase)
@@ -2205,7 +2205,7 @@ fn make_search_word_bounded(cx: &mut Context) {
     let register = cx
         .register
         .unwrap_or(cx.editor.registers.last_search_register);
-    let regex = match cx.editor.registers.first(register, cx.editor) {
+    let regex = match cx.editor.registers.latest(register, cx.editor) {
         Some(regex) => regex,
         None => return,
     };

helix-term/src/ui/prompt.rs

@@ -133,7 +133,7 @@ impl Prompt {
         editor: &'a Editor,
     ) -> Option<Cow<'a, str>> {
         self.history_register
-            .and_then(|reg| editor.registers.first(reg, editor))
+            .and_then(|reg| editor.registers.latest(reg, editor))
     }
 
     pub fn recalculate_completion(&mut self, editor: &Editor) {
@@ -656,7 +656,7 @@ impl Component for Prompt {
                         &context
                             .editor
                             .registers
-                            .first(c, context.editor)
+                            .latest(c, context.editor)
                             .unwrap_or_default(),
                         context.editor,
                     );

helix-view/src/register.rs

@@ -216,14 +216,59 @@ impl Registers {
         }
     }
 
-    pub fn first<'a>(&'a self, name: char, editor: &'a Editor) -> Option<Cow<'a, str>> {
-        self.read(name, editor).and_then(|mut values| values.next())
+    /// "Selects" the index at the given index for the given register.
+    ///
+    /// Selecting an item pulls it to the front of the register's history.
+    ///
+    /// If the register is a special register other than a clipboard register ('+' or '*')
+    /// or if the index is out of bounds for the given register, this command is a no-op.
+    pub fn select_history_entry(&mut self, name: char, index: usize) -> Result<()> {
+        match name {
+            '_' | '#' | '.' | '%' => {
+                Err(anyhow::anyhow!("Register {name} does not support writing"))
+            }
+            _ => {
+                let Some(register) = self.inner.get_mut(&name) else {
+                    return Ok(());
+                };
+                register.select_history_entry(index);
+                self.sync_clipboard_register(name)
+            }
+        }
+    }
+
+    fn sync_clipboard_register(&mut self, name: char) -> Result<()> {
+        let clipboard_type = match name {
+            '+' => ClipboardType::Clipboard,
+            '*' => ClipboardType::Selection,
+            _ => return Ok(()),
+        };
+
+        let mut contents = String::new();
+        for val in self.inner[&name].values() {
+            if !contents.is_empty() {
+                contents.push_str(NATIVE_LINE_ENDING.as_str());
+            }
+            contents.push_str(&val);
+        }
+        self.clipboard_provider
+            .set_contents(contents, clipboard_type)
     }
 
-    pub fn last<'a>(&'a self, name: char, editor: &'a Editor) -> Option<Cow<'a, str>> {
+    /// Returns the latest value in the given register.
+    ///
+    /// The latest value is the value most recently pushed to the register when
+    /// using `push`, or the last value returned by the iterator passed to [write].
+    pub fn latest<'a>(&'a self, name: char, editor: &'a Editor) -> Option<Cow<'a, str>> {
         self.read(name, editor).and_then(|values| values.last())
     }
 
+    /// Returns the oldest value in the given register.
+    /// This is the opposite of `latest`.
+    pub fn oldest<'a>(&'a self, name: char, editor: &'a Editor) -> Option<Cow<'a, str>> {
+        self.read(name, editor).and_then(|mut values| values.next())
+    }
+
     pub fn iter_preview(&self) -> impl Iterator<Item = (char, &str)> {
         self.inner
             .iter()