Improve installation of npm-based language servers

* Use --prefix flag to guarantee that they are installed in .zed
* Use the @latest tag when available
* Extract helper functions

Co-authored-by: Keith Simmons <keith@zed.dev>

crates/zed/src/languages/installation.rs

@@ -0,0 +1,111 @@
+use anyhow::{anyhow, Context, Result};
+use client::http::{self, HttpClient, Method};
+use serde::Deserialize;
+use std::{path::Path, sync::Arc};
+
+pub struct GitHubLspBinaryVersion {
+    pub name: String,
+    pub url: http::Url,
+}
+
+#[derive(Deserialize)]
+#[serde(rename_all = "kebab-case")]
+struct NpmInfo {
+    #[serde(default)]
+    dist_tags: NpmInfoDistTags,
+    versions: Vec<String>,
+}
+
+#[derive(Deserialize, Default)]
+struct NpmInfoDistTags {
+    latest: Option<String>,
+}
+
+#[derive(Deserialize)]
+pub(crate) struct GithubRelease {
+    name: String,
+    assets: Vec<GithubReleaseAsset>,
+}
+
+#[derive(Deserialize)]
+pub(crate) struct GithubReleaseAsset {
+    name: String,
+    browser_download_url: http::Url,
+}
+
+pub async fn npm_package_latest_version(name: &str) -> Result<String> {
+    let output = smol::process::Command::new("npm")
+        .args(["info", name, "--json"])
+        .output()
+        .await?;
+    if !output.status.success() {
+        Err(anyhow!(
+            "failed to execute npm info: {:?}",
+            String::from_utf8_lossy(&output.stderr)
+        ))?;
+    }
+    let mut info: NpmInfo = serde_json::from_slice(&output.stdout)?;
+    info.dist_tags
+        .latest
+        .or_else(|| info.versions.pop())
+        .ok_or_else(|| anyhow!("no version found for npm package {}", name))
+}
+
+pub async fn npm_install_packages(
+    packages: impl IntoIterator<Item = (&str, &str)>,
+    directory: &Path,
+) -> Result<()> {
+    let output = smol::process::Command::new("npm")
+        .arg("install")
+        .arg("--prefix")
+        .arg(directory)
+        .args(
+            packages
+                .into_iter()
+                .map(|(name, version)| format!("{name}@{version}")),
+        )
+        .output()
+        .await
+        .context("failed to run npm install")?;
+    if !output.status.success() {
+        Err(anyhow!(
+            "failed to execute npm install: {:?}",
+            String::from_utf8_lossy(&output.stderr)
+        ))?;
+    }
+    Ok(())
+}
+
+pub async fn latest_github_release(
+    repo_name_with_owner: &str,
+    http: Arc<dyn HttpClient>,
+    asset_name: impl Fn(&str) -> String,
+) -> Result<GitHubLspBinaryVersion> {
+    let release = http
+        .send(
+            surf::RequestBuilder::new(
+                Method::Get,
+                http::Url::parse(&format!(
+                    "https://api.github.com/repos/{repo_name_with_owner}/releases/latest"
+                ))
+                .unwrap(),
+            )
+            .middleware(surf::middleware::Redirect::default())
+            .build(),
+        )
+        .await
+        .map_err(|err| anyhow!("error fetching latest release: {}", err))?
+        .body_json::<GithubRelease>()
+        .await
+        .map_err(|err| anyhow!("error parsing latest release: {}", err))?;
+    let asset_name = asset_name(&release.name);
+    let asset = release
+        .assets
+        .iter()
+        .find(|asset| asset.name == asset_name)
+        .ok_or_else(|| anyhow!("no asset found matching {:?}", asset_name))?;
+    Ok(GitHubLspBinaryVersion {
+        name: release.name,
+        url: asset.browser_download_url.clone(),
+    })
+}