Extract PromptStore and PromptBuilder to new prompt_library crate (#23254)

This PR adds a new `prompt_library` crate and extracts the `PromptStore`
and `PromptBuilder` to it.

Eventually we'll want to house the `PromptLibrary` itself in this crate,
but right now that involves untangling a few dependencies.

Release Notes:

- N/A

crates/prompt_library/src/prompts.rs

@@ -0,0 +1,326 @@
+use anyhow::Result;
+use assets::Assets;
+use fs::Fs;
+use futures::StreamExt;
+use gpui::AssetSource;
+use handlebars::{Handlebars, RenderError};
+use language::{BufferSnapshot, LanguageName, Point};
+use parking_lot::Mutex;
+use serde::Serialize;
+use std::{ops::Range, path::PathBuf, sync::Arc, time::Duration};
+use text::LineEnding;
+use util::ResultExt;
+
+#[derive(Serialize)]
+pub struct ContentPromptDiagnosticContext {
+    pub line_number: usize,
+    pub error_message: String,
+    pub code_content: String,
+}
+
+#[derive(Serialize)]
+pub struct ContentPromptContext {
+    pub content_type: String,
+    pub language_name: Option<String>,
+    pub is_insert: bool,
+    pub is_truncated: bool,
+    pub document_content: String,
+    pub user_prompt: String,
+    pub rewrite_section: Option<String>,
+    pub diagnostic_errors: Vec<ContentPromptDiagnosticContext>,
+}
+
+#[derive(Serialize)]
+pub struct TerminalAssistantPromptContext {
+    pub os: String,
+    pub arch: String,
+    pub shell: Option<String>,
+    pub working_directory: Option<String>,
+    pub latest_output: Vec<String>,
+    pub user_prompt: String,
+}
+
+#[derive(Serialize)]
+pub struct ProjectSlashCommandPromptContext {
+    pub context_buffer: String,
+}
+
+pub struct PromptLoadingParams<'a> {
+    pub fs: Arc<dyn Fs>,
+    pub repo_path: Option<PathBuf>,
+    pub cx: &'a gpui::AppContext,
+}
+
+pub struct PromptBuilder {
+    handlebars: Arc<Mutex<Handlebars<'static>>>,
+}
+
+impl PromptBuilder {
+    pub fn new(loading_params: Option<PromptLoadingParams>) -> Result<Self> {
+        let mut handlebars = Handlebars::new();
+        Self::register_built_in_templates(&mut handlebars)?;
+
+        let handlebars = Arc::new(Mutex::new(handlebars));
+
+        if let Some(params) = loading_params {
+            Self::watch_fs_for_template_overrides(params, handlebars.clone());
+        }
+
+        Ok(Self { handlebars })
+    }
+
+    /// Watches the filesystem for changes to prompt template overrides.
+    ///
+    /// This function sets up a file watcher on the prompt templates directory. It performs
+    /// an initial scan of the directory and registers any existing template overrides.
+    /// Then it continuously monitors for changes, reloading templates as they are
+    /// modified or added.
+    ///
+    /// If the templates directory doesn't exist initially, it waits for it to be created.
+    /// If the directory is removed, it restores the built-in templates and waits for the
+    /// directory to be recreated.
+    ///
+    /// # Arguments
+    ///
+    /// * `params` - A `PromptLoadingParams` struct containing the filesystem, repository path,
+    ///   and application context.
+    /// * `handlebars` - An `Arc<Mutex<Handlebars>>` for registering and updating templates.
+    fn watch_fs_for_template_overrides(
+        params: PromptLoadingParams,
+        handlebars: Arc<Mutex<Handlebars<'static>>>,
+    ) {
+        let templates_dir = paths::prompt_overrides_dir(params.repo_path.as_deref());
+        params.cx.background_executor()
+            .spawn(async move {
+                let Some(parent_dir) = templates_dir.parent() else {
+                    return;
+                };
+
+                let mut found_dir_once = false;
+                loop {
+                    // Check if the templates directory exists and handle its status
+                    // If it exists, log its presence and check if it's a symlink
+                    // If it doesn't exist:
+                    //   - Log that we're using built-in prompts
+                    //   - Check if it's a broken symlink and log if so
+                    //   - Set up a watcher to detect when it's created
+                    // After the first check, set the `found_dir_once` flag
+                    // This allows us to avoid logging when looping back around after deleting the prompt overrides directory.
+                    let dir_status = params.fs.is_dir(&templates_dir).await;
+                    let symlink_status = params.fs.read_link(&templates_dir).await.ok();
+                    if dir_status {
+                        let mut log_message = format!("Prompt template overrides directory found at {}", templates_dir.display());
+                        if let Some(target) = symlink_status {
+                            log_message.push_str(" -> ");
+                            log_message.push_str(&target.display().to_string());
+                        }
+                        log::info!("{}.", log_message);
+                    } else {
+                        if !found_dir_once {
+                            log::info!("No prompt template overrides directory found at {}. Using built-in prompts.", templates_dir.display());
+                            if let Some(target) = symlink_status {
+                                log::info!("Symlink found pointing to {}, but target is invalid.", target.display());
+                            }
+                        }
+
+                        if params.fs.is_dir(parent_dir).await {
+                            let (mut changes, _watcher) = params.fs.watch(parent_dir, Duration::from_secs(1)).await;
+                            while let Some(changed_paths) = changes.next().await {
+                                if changed_paths.iter().any(|p| &p.path == &templates_dir) {
+                                    let mut log_message = format!("Prompt template overrides directory detected at {}", templates_dir.display());
+                                    if let Ok(target) = params.fs.read_link(&templates_dir).await {
+                                        log_message.push_str(" -> ");
+                                        log_message.push_str(&target.display().to_string());
+                                    }
+                                    log::info!("{}.", log_message);
+                                    break;
+                                }
+                            }
+                        } else {
+                            return;
+                        }
+                    }
+
+                    found_dir_once = true;
+
+                    // Initial scan of the prompt overrides directory
+                    if let Ok(mut entries) = params.fs.read_dir(&templates_dir).await {
+                        while let Some(Ok(file_path)) = entries.next().await {
+                            if file_path.to_string_lossy().ends_with(".hbs") {
+                                if let Ok(content) = params.fs.load(&file_path).await {
+                                    let file_name = file_path.file_stem().unwrap().to_string_lossy();
+                                    log::debug!("Registering prompt template override: {}", file_name);
+                                    handlebars.lock().register_template_string(&file_name, content).log_err();
+                                }
+                            }
+                        }
+                    }
+
+                    // Watch both the parent directory and the template overrides directory:
+                    // - Monitor the parent directory to detect if the template overrides directory is deleted.
+                    // - Monitor the template overrides directory to re-register templates when they change.
+                    // Combine both watch streams into a single stream.
+                    let (parent_changes, parent_watcher) = params.fs.watch(parent_dir, Duration::from_secs(1)).await;
+                    let (changes, watcher) = params.fs.watch(&templates_dir, Duration::from_secs(1)).await;
+                    let mut combined_changes = futures::stream::select(changes, parent_changes);
+
+                    while let Some(changed_paths) = combined_changes.next().await {
+                        if changed_paths.iter().any(|p| &p.path == &templates_dir) {
+                            if !params.fs.is_dir(&templates_dir).await {
+                                log::info!("Prompt template overrides directory removed. Restoring built-in prompt templates.");
+                                Self::register_built_in_templates(&mut handlebars.lock()).log_err();
+                                break;
+                            }
+                        }
+                        for event in changed_paths {
+                            if event.path.starts_with(&templates_dir) && event.path.extension().map_or(false, |ext| ext == "hbs") {
+                                log::info!("Reloading prompt template override: {}", event.path.display());
+                                if let Some(content) = params.fs.load(&event.path).await.log_err() {
+                                    let file_name = event.path.file_stem().unwrap().to_string_lossy();
+                                    handlebars.lock().register_template_string(&file_name, content).log_err();
+                                }
+                            }
+                        }
+                    }
+
+                    drop(watcher);
+                    drop(parent_watcher);
+                }
+            })
+            .detach();
+    }
+
+    fn register_built_in_templates(handlebars: &mut Handlebars) -> Result<()> {
+        for path in Assets.list("prompts")? {
+            if let Some(id) = path.split('/').last().and_then(|s| s.strip_suffix(".hbs")) {
+                if let Some(prompt) = Assets.load(path.as_ref()).log_err().flatten() {
+                    log::debug!("Registering built-in prompt template: {}", id);
+                    let prompt = String::from_utf8_lossy(prompt.as_ref());
+                    handlebars.register_template_string(id, LineEnding::normalize_cow(prompt))?
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    pub fn generate_inline_transformation_prompt(
+        &self,
+        user_prompt: String,
+        language_name: Option<&LanguageName>,
+        buffer: BufferSnapshot,
+        range: Range<usize>,
+    ) -> Result<String, RenderError> {
+        let content_type = match language_name.as_ref().map(|l| l.0.as_ref()) {
+            None | Some("Markdown" | "Plain Text") => "text",
+            Some(_) => "code",
+        };
+
+        const MAX_CTX: usize = 50000;
+        let is_insert = range.is_empty();
+        let mut is_truncated = false;
+
+        let before_range = 0..range.start;
+        let truncated_before = if before_range.len() > MAX_CTX {
+            is_truncated = true;
+            let start = buffer.clip_offset(range.start - MAX_CTX, text::Bias::Right);
+            start..range.start
+        } else {
+            before_range
+        };
+
+        let after_range = range.end..buffer.len();
+        let truncated_after = if after_range.len() > MAX_CTX {
+            is_truncated = true;
+            let end = buffer.clip_offset(range.end + MAX_CTX, text::Bias::Left);
+            range.end..end
+        } else {
+            after_range
+        };
+
+        let mut document_content = String::new();
+        for chunk in buffer.text_for_range(truncated_before) {
+            document_content.push_str(chunk);
+        }
+        if is_insert {
+            document_content.push_str("<insert_here></insert_here>");
+        } else {
+            document_content.push_str("<rewrite_this>\n");
+            for chunk in buffer.text_for_range(range.clone()) {
+                document_content.push_str(chunk);
+            }
+            document_content.push_str("\n</rewrite_this>");
+        }
+        for chunk in buffer.text_for_range(truncated_after) {
+            document_content.push_str(chunk);
+        }
+
+        let rewrite_section = if !is_insert {
+            let mut section = String::new();
+            for chunk in buffer.text_for_range(range.clone()) {
+                section.push_str(chunk);
+            }
+            Some(section)
+        } else {
+            None
+        };
+        let diagnostics = buffer.diagnostics_in_range::<_, Point>(range, false);
+        let diagnostic_errors: Vec<ContentPromptDiagnosticContext> = diagnostics
+            .map(|entry| {
+                let start = entry.range.start;
+                ContentPromptDiagnosticContext {
+                    line_number: (start.row + 1) as usize,
+                    error_message: entry.diagnostic.message.clone(),
+                    code_content: buffer.text_for_range(entry.range.clone()).collect(),
+                }
+            })
+            .collect();
+
+        let context = ContentPromptContext {
+            content_type: content_type.to_string(),
+            language_name: language_name.map(|s| s.to_string()),
+            is_insert,
+            is_truncated,
+            document_content,
+            user_prompt,
+            rewrite_section,
+            diagnostic_errors,
+        };
+        self.handlebars.lock().render("content_prompt", &context)
+    }
+
+    pub fn generate_terminal_assistant_prompt(
+        &self,
+        user_prompt: &str,
+        shell: Option<&str>,
+        working_directory: Option<&str>,
+        latest_output: &[String],
+    ) -> Result<String, RenderError> {
+        let context = TerminalAssistantPromptContext {
+            os: std::env::consts::OS.to_string(),
+            arch: std::env::consts::ARCH.to_string(),
+            shell: shell.map(|s| s.to_string()),
+            working_directory: working_directory.map(|s| s.to_string()),
+            latest_output: latest_output.to_vec(),
+            user_prompt: user_prompt.to_string(),
+        };
+
+        self.handlebars
+            .lock()
+            .render("terminal_assistant_prompt", &context)
+    }
+
+    pub fn generate_suggest_edits_prompt(&self) -> Result<String, RenderError> {
+        self.handlebars.lock().render("suggest_edits", &())
+    }
+
+    pub fn generate_project_slash_command_prompt(
+        &self,
+        context_buffer: String,
+    ) -> Result<String, RenderError> {
+        self.handlebars.lock().render(
+            "project_slash_command",
+            &ProjectSlashCommandPromptContext { context_buffer },
+        )
+    }
+}