Extract slash commands to their own crate (#23261)

This PR extracts the slash command definitions out of the `assistant`
crate and into their own `assistant_slash_commands` crate.

Release Notes:

- N/A

crates/assistant_slash_commands/src/fetch_command.rs

@@ -0,0 +1,178 @@
+use std::cell::RefCell;
+use std::rc::Rc;
+use std::sync::atomic::AtomicBool;
+use std::sync::Arc;
+
+use anyhow::{anyhow, bail, Context, Result};
+use assistant_slash_command::{
+    ArgumentCompletion, SlashCommand, SlashCommandOutput, SlashCommandOutputSection,
+    SlashCommandResult,
+};
+use futures::AsyncReadExt;
+use gpui::{Task, WeakView};
+use html_to_markdown::{convert_html_to_markdown, markdown, TagHandler};
+use http_client::{AsyncBody, HttpClient, HttpClientWithUrl};
+use language::{BufferSnapshot, LspAdapterDelegate};
+use ui::prelude::*;
+use workspace::Workspace;
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
+enum ContentType {
+    Html,
+    Plaintext,
+    Json,
+}
+
+pub struct FetchSlashCommand;
+
+impl FetchSlashCommand {
+    async fn build_message(http_client: Arc<HttpClientWithUrl>, url: &str) -> Result<String> {
+        let mut url = url.to_owned();
+        if !url.starts_with("https://") && !url.starts_with("http://") {
+            url = format!("https://{url}");
+        }
+
+        let mut response = http_client.get(&url, AsyncBody::default(), true).await?;
+
+        let mut body = Vec::new();
+        response
+            .body_mut()
+            .read_to_end(&mut body)
+            .await
+            .context("error reading response body")?;
+
+        if response.status().is_client_error() {
+            let text = String::from_utf8_lossy(body.as_slice());
+            bail!(
+                "status error {}, response: {text:?}",
+                response.status().as_u16()
+            );
+        }
+
+        let Some(content_type) = response.headers().get("content-type") else {
+            bail!("missing Content-Type header");
+        };
+        let content_type = content_type
+            .to_str()
+            .context("invalid Content-Type header")?;
+        let content_type = match content_type {
+            "text/html" => ContentType::Html,
+            "text/plain" => ContentType::Plaintext,
+            "application/json" => ContentType::Json,
+            _ => ContentType::Html,
+        };
+
+        match content_type {
+            ContentType::Html => {
+                let mut handlers: Vec<TagHandler> = vec![
+                    Rc::new(RefCell::new(markdown::WebpageChromeRemover)),
+                    Rc::new(RefCell::new(markdown::ParagraphHandler)),
+                    Rc::new(RefCell::new(markdown::HeadingHandler)),
+                    Rc::new(RefCell::new(markdown::ListHandler)),
+                    Rc::new(RefCell::new(markdown::TableHandler::new())),
+                    Rc::new(RefCell::new(markdown::StyledTextHandler)),
+                ];
+                if url.contains("wikipedia.org") {
+                    use html_to_markdown::structure::wikipedia;
+
+                    handlers.push(Rc::new(RefCell::new(wikipedia::WikipediaChromeRemover)));
+                    handlers.push(Rc::new(RefCell::new(wikipedia::WikipediaInfoboxHandler)));
+                    handlers.push(Rc::new(
+                        RefCell::new(wikipedia::WikipediaCodeHandler::new()),
+                    ));
+                } else {
+                    handlers.push(Rc::new(RefCell::new(markdown::CodeHandler)));
+                }
+
+                convert_html_to_markdown(&body[..], &mut handlers)
+            }
+            ContentType::Plaintext => Ok(std::str::from_utf8(&body)?.to_owned()),
+            ContentType::Json => {
+                let json: serde_json::Value = serde_json::from_slice(&body)?;
+
+                Ok(format!(
+                    "```json\n{}\n```",
+                    serde_json::to_string_pretty(&json)?
+                ))
+            }
+        }
+    }
+}
+
+impl SlashCommand for FetchSlashCommand {
+    fn name(&self) -> String {
+        "fetch".into()
+    }
+
+    fn description(&self) -> String {
+        "Insert fetched URL contents".into()
+    }
+
+    fn icon(&self) -> IconName {
+        IconName::Globe
+    }
+
+    fn menu_text(&self) -> String {
+        self.description()
+    }
+
+    fn requires_argument(&self) -> bool {
+        true
+    }
+
+    fn complete_argument(
+        self: Arc<Self>,
+        _arguments: &[String],
+        _cancel: Arc<AtomicBool>,
+        _workspace: Option<WeakView<Workspace>>,
+        _cx: &mut WindowContext,
+    ) -> Task<Result<Vec<ArgumentCompletion>>> {
+        Task::ready(Ok(Vec::new()))
+    }
+
+    fn run(
+        self: Arc<Self>,
+        arguments: &[String],
+        _context_slash_command_output_sections: &[SlashCommandOutputSection<language::Anchor>],
+        _context_buffer: BufferSnapshot,
+        workspace: WeakView<Workspace>,
+        _delegate: Option<Arc<dyn LspAdapterDelegate>>,
+        cx: &mut WindowContext,
+    ) -> Task<SlashCommandResult> {
+        let Some(argument) = arguments.first() else {
+            return Task::ready(Err(anyhow!("missing URL")));
+        };
+        let Some(workspace) = workspace.upgrade() else {
+            return Task::ready(Err(anyhow!("workspace was dropped")));
+        };
+
+        let http_client = workspace.read(cx).client().http_client();
+        let url = argument.to_string();
+
+        let text = cx.background_executor().spawn({
+            let url = url.clone();
+            async move { Self::build_message(http_client, &url).await }
+        });
+
+        let url = SharedString::from(url);
+        cx.foreground_executor().spawn(async move {
+            let text = text.await?;
+            if text.trim().is_empty() {
+                bail!("no textual content found");
+            }
+
+            let range = 0..text.len();
+            Ok(SlashCommandOutput {
+                text,
+                sections: vec![SlashCommandOutputSection {
+                    range,
+                    icon: IconName::Globe,
+                    label: format!("fetch {}", url).into(),
+                    metadata: None,
+                }],
+                run_commands_in_text: false,
+            }
+            .to_event_stream())
+        })
+    }
+}