Introduce a new /tabs command (#12382)

This inserts the content of the open tabs sorted by recency.

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/assistant/src/slash_command/tabs_command.rs

@@ -0,0 +1,116 @@
+use super::{file_command::FilePlaceholder, SlashCommand, SlashCommandOutput};
+use anyhow::{anyhow, Result};
+use assistant_slash_command::SlashCommandOutputSection;
+use collections::HashMap;
+use editor::Editor;
+use gpui::{AppContext, Entity, Task, WeakView};
+use language::LspAdapterDelegate;
+use std::{fmt::Write, path::Path, sync::Arc};
+use ui::{IntoElement, WindowContext};
+use workspace::Workspace;
+
+pub(crate) struct TabsSlashCommand;
+
+impl SlashCommand for TabsSlashCommand {
+    fn name(&self) -> String {
+        "tabs".into()
+    }
+
+    fn description(&self) -> String {
+        "insert content from open tabs".into()
+    }
+
+    fn tooltip_text(&self) -> String {
+        "insert open tabs".into()
+    }
+
+    fn requires_argument(&self) -> bool {
+        false
+    }
+
+    fn complete_argument(
+        &self,
+        _query: String,
+        _cancel: Arc<std::sync::atomic::AtomicBool>,
+        _cx: &mut AppContext,
+    ) -> Task<Result<Vec<String>>> {
+        Task::ready(Err(anyhow!("this command does not require argument")))
+    }
+
+    fn run(
+        self: Arc<Self>,
+        _argument: Option<&str>,
+        workspace: WeakView<Workspace>,
+        _delegate: Arc<dyn LspAdapterDelegate>,
+        cx: &mut WindowContext,
+    ) -> Task<Result<SlashCommandOutput>> {
+        let open_buffers = workspace.update(cx, |workspace, cx| {
+            let mut timestamps_by_entity_id = HashMap::default();
+            let mut open_buffers = Vec::new();
+
+            for pane in workspace.panes() {
+                let pane = pane.read(cx);
+                for entry in pane.activation_history() {
+                    timestamps_by_entity_id.insert(entry.entity_id, entry.timestamp);
+                }
+            }
+
+            for editor in workspace.items_of_type::<Editor>(cx) {
+                if let Some(buffer) = editor.read(cx).buffer().read(cx).as_singleton() {
+                    if let Some(timestamp) = timestamps_by_entity_id.get(&editor.entity_id()) {
+                        let snapshot = buffer.read(cx).snapshot();
+                        let full_path = snapshot.resolve_file_path(cx, true);
+                        open_buffers.push((full_path, snapshot, *timestamp));
+                    }
+                }
+            }
+
+            open_buffers
+        });
+
+        match open_buffers {
+            Ok(mut open_buffers) => cx.background_executor().spawn(async move {
+                open_buffers.sort_by_key(|(_, _, timestamp)| *timestamp);
+
+                let mut sections = Vec::new();
+                let mut text = String::new();
+                for (full_path, buffer, _) in open_buffers {
+                    let section_start_ix = text.len();
+                    writeln!(
+                        text,
+                        "```{}\n",
+                        full_path
+                            .as_deref()
+                            .unwrap_or(Path::new("untitled"))
+                            .display()
+                    )
+                    .unwrap();
+                    for chunk in buffer.as_rope().chunks() {
+                        text.push_str(chunk);
+                    }
+                    if !text.ends_with('\n') {
+                        text.push('\n');
+                    }
+                    writeln!(text, "```\n").unwrap();
+                    let section_end_ix = text.len() - 1;
+
+                    sections.push(SlashCommandOutputSection {
+                        range: section_start_ix..section_end_ix,
+                        render_placeholder: Arc::new(move |id, unfold, _| {
+                            FilePlaceholder {
+                                id,
+                                path: full_path.clone(),
+                                line_range: None,
+                                unfold,
+                            }
+                            .into_any_element()
+                        }),
+                    });
+                }
+
+                Ok(SlashCommandOutput { text, sections })
+            }),
+            Err(error) => Task::ready(Err(error)),
+        }
+    }
+}