Introduce a new /workflow command (#15854)

This subsumes the previous built-in prompt.

Release Notes:

- N/A

crates/assistant/src/slash_command/workflow_command.rs

@@ -0,0 +1,71 @@
+use std::sync::atomic::AtomicBool;
+use std::sync::Arc;
+
+use anyhow::{Context as _, Result};
+use assets::Assets;
+use assistant_slash_command::{
+    ArgumentCompletion, SlashCommand, SlashCommandOutput, SlashCommandOutputSection,
+};
+use gpui::{AppContext, AssetSource, Task, WeakView};
+use language::LspAdapterDelegate;
+use text::LineEnding;
+use ui::prelude::*;
+use workspace::Workspace;
+
+pub(crate) struct WorkflowSlashCommand;
+
+impl SlashCommand for WorkflowSlashCommand {
+    fn name(&self) -> String {
+        "workflow".into()
+    }
+
+    fn description(&self) -> String {
+        "insert a prompt that opts into the edit workflow".into()
+    }
+
+    fn menu_text(&self) -> String {
+        "Insert Workflow Prompt".into()
+    }
+
+    fn requires_argument(&self) -> bool {
+        false
+    }
+
+    fn complete_argument(
+        self: Arc<Self>,
+        _query: String,
+        _cancel: Arc<AtomicBool>,
+        _workspace: Option<WeakView<Workspace>>,
+        _cx: &mut AppContext,
+    ) -> Task<Result<Vec<ArgumentCompletion>>> {
+        Task::ready(Ok(Vec::new()))
+    }
+
+    fn run(
+        self: Arc<Self>,
+        _argument: Option<&str>,
+        _workspace: WeakView<Workspace>,
+        _delegate: Option<Arc<dyn LspAdapterDelegate>>,
+        _cx: &mut WindowContext,
+    ) -> Task<Result<SlashCommandOutput>> {
+        let mut text = match Assets
+            .load("prompts/edit_workflow.md")
+            .and_then(|prompt| prompt.context("prompts/edit_workflow.md not found"))
+        {
+            Ok(prompt) => String::from_utf8_lossy(&prompt).into_owned(),
+            Err(error) => return Task::ready(Err(error)),
+        };
+        LineEnding::normalize(&mut text);
+        let range = 0..text.len();
+
+        Task::ready(Ok(SlashCommandOutput {
+            text,
+            sections: vec![SlashCommandOutputSection {
+                range,
+                icon: IconName::Route,
+                label: "Workflow".into(),
+            }],
+            run_commands_in_text: false,
+        }))
+    }
+}