Only require setuptools when an initial attempt fails

Cargo.toml

@@ -54,6 +54,7 @@ sha2 = "0.10"
 snafu = "0.7"
 tar = "0.4"
 spinners = "4"
+tempfile = "3.12"
 testutils = { path = "crates/testutils" }
 tmpdir = "1.0"
 tokio = { version = "1", features = ["full"] }

crates/tower-runtime/src/local.rs

@@ -275,7 +275,49 @@ async fn execute_local_app(
                 ));
 
                 // Let's wait for the setup to finish. We don't care about the results.
-                let res = wait_for_process(ctx.clone(), &cancel_token, child).await;
+                let mut res = wait_for_process(ctx.clone(), &cancel_token, child).await;
+
+                // If the requirements.txt install failed, retry with the legacy
+                // setuptools<82 pin. Some apps (those whose transitive deps rely on
+                // pkg_resources) need that pin to install successfully; we don't
+                // apply it by default because it conflicts with apps whose deps
+                // require setuptools>=82.
+                if res != 0 && uv.should_use_legacy_setuptools_pin(&working_dir) {
+                    let _ = opts.output_sender.send(Output {
+                        channel: Channel::Setup,
+                        fd: FD::Stdout,
+                        line: "tower: dependency install failed; retrying with setuptools<82 pin for pkg_resources compatibility".to_string(),
+                        time: chrono::Utc::now(),
+                    });
+
+                    match uv
+                        .sync_with_legacy_setuptools_pin(&working_dir, &env_vars)
+                        .await
+                    {
+                        Err(e) => {
+                            return Err(e.into());
+                        }
+                        Ok(mut retry_child) => {
+                            let stdout = retry_child.stdout.take().expect("no stdout");
+                            tokio::spawn(drain_output(
+                                FD::Stdout,
+                                Channel::Setup,
+                                opts.output_sender.clone(),
+                                BufReader::new(stdout),
+                            ));
+
+                            let stderr = retry_child.stderr.take().expect("no stderr");
+                            tokio::spawn(drain_output(
+                                FD::Stderr,
+                                Channel::Setup,
+                                opts.output_sender.clone(),
+                                BufReader::new(stderr),
+                            ));
+
+                            res = wait_for_process(ctx.clone(), &cancel_token, retry_child).await;
+                        }
+                    }
+                }
 
                 if res != 0 {
                     // If the sync process failed, we want to return an error.

crates/tower-uv/Cargo.toml

@@ -19,3 +19,6 @@ seahash = { workspace = true }
 tokio = { workspace = true }
 tokio-tar = { workspace = true }
 tower-telemetry = { workspace = true }
+
+[dev-dependencies]
+tempfile = { workspace = true }

crates/tower-uv/src/lib.rs

@@ -357,44 +357,85 @@ impl Uv {
                 &self.uv_path, cwd
             );
 
-            // If there is a requirements.txt, then we can use that to sync.
-            let mut cmd = Command::new(&self.uv_path);
-            cmd.kill_on_drop(true)
-                .stdin(Stdio::null())
-                .stdout(Stdio::piped())
-                .stderr(Stdio::piped())
-                .current_dir(cwd)
-                .arg("--color")
-                .arg("never")
-                .arg("pip")
-                .arg("install")
-                .arg("-r")
-                .arg(cwd.join("requirements.txt"))
-                // setuptools 82 removed pkg_resources, but many legacy packages
-                // still import it without declaring the dependency. Let's always install
-                // a version that includes pkg_resources for requirements.txt, on the
-                // basis that requirements.txt projects are probably not using the latest
-                // and greatest deps (then they'd likely be using pyproject.toml anyway)
-                // https://github.com/pypa/setuptools/issues/5174
-                .arg("setuptools<82")
-                .envs(env_vars);
+            self.spawn_requirements_install(cwd, env_vars, false).await
+        } else {
+            // If there is no pyproject.toml or requirements.txt, then we can't sync.
+            Err(Error::MissingPyprojectToml)
+        }
+    }
 
-            #[cfg(unix)]
-            {
-                cmd.process_group(0);
-            }
+    /// Returns whether a failed `sync()` for this directory is eligible for a
+    /// retry via [`sync_with_legacy_setuptools_pin`]. Only applies to projects
+    /// driven by `requirements.txt`; pyproject-based projects manage their own
+    /// setuptools dependency.
+    pub fn should_use_legacy_setuptools_pin(&self, cwd: &Path) -> bool {
+        cwd.join("requirements.txt").exists()
+    }
 
-            if let Some(dir) = &self.cache_dir {
-                cmd.arg("--cache-dir").arg(dir);
-            }
+    /// Re-runs the `requirements.txt` install with a `setuptools<82` pin appended.
+    ///
+    /// setuptools 82 removed `pkg_resources`, but many legacy packages still import
+    /// it without declaring the dependency. Pinning `setuptools<82` keeps it
+    /// available. Some modern packages (e.g. dlt's transitive graph pinning
+    /// `setuptools==82.0.1`) make this pin unsatisfiable, so it isn't applied up
+    /// front — callers should fall back to this only after a plain `sync()`
+    /// fails for a project using `requirements.txt`.
+    ///
+    /// https://github.com/pypa/setuptools/issues/5174
+    pub async fn sync_with_legacy_setuptools_pin(
+        &self,
+        cwd: &PathBuf,
+        env_vars: &HashMap<String, String>,
+    ) -> Result<Child, Error> {
+        if !cwd.join("requirements.txt").exists() {
+            return Err(Error::MissingPyprojectToml);
+        }
 
-            let child = cmd.spawn()?;
+        debug!(
+            "Retrying UV ({:?}) sync with setuptools<82 pin in {:?}",
+            &self.uv_path, cwd
+        );
 
-            Ok(child)
-        } else {
-            // If there is no pyproject.toml or requirements.txt, then we can't sync.
-            Err(Error::MissingPyprojectToml)
+        self.spawn_requirements_install(cwd, env_vars, true).await
+    }
+
+    async fn spawn_requirements_install(
+        &self,
+        cwd: &PathBuf,
+        env_vars: &HashMap<String, String>,
+        pin_legacy_setuptools: bool,
+    ) -> Result<Child, Error> {
+        let req_path = cwd.join("requirements.txt");
+
+        let mut cmd = Command::new(&self.uv_path);
+        cmd.kill_on_drop(true)
+            .stdin(Stdio::null())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped())
+            .current_dir(cwd)
+            .arg("--color")
+            .arg("never")
+            .arg("pip")
+            .arg("install")
+            .arg("-r")
+            .arg(&req_path);
+
+        if pin_legacy_setuptools {
+            cmd.arg("setuptools<82");
         }
+
+        cmd.envs(env_vars);
+
+        #[cfg(unix)]
+        {
+            cmd.process_group(0);
+        }
+
+        if let Some(dir) = &self.cache_dir {
+            cmd.arg("--cache-dir").arg(dir);
+        }
+
+        Ok(cmd.spawn()?)
     }
 
     pub async fn run(

crates/tower-uv/tests/sync_test.rs

@@ -0,0 +1,130 @@
+//! Integration tests for `Uv::sync` requirements.txt handling.
+//!
+//! `sync()` runs a plain `uv pip install -r requirements.txt` (no setuptools
+//! pin). Callers that hit a resolution failure can retry via
+//! `sync_with_legacy_setuptools_pin()` for the legacy `pkg_resources`
+//! compatibility case. The retry orchestration lives in
+//! `tower-runtime::local`.
+//!
+//! These tests shell out to a real `uv` binary and hit pypi, mirroring the
+//! existing `install_test.rs`.
+
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+use tempfile::TempDir;
+use tokio::process::Child;
+use tower_uv::Uv;
+
+async fn wait(mut child: Child) -> i32 {
+    let status = child.wait().await.expect("wait failed");
+    status.code().unwrap_or(-1)
+}
+
+async fn make_uv_with_venv(cwd: &PathBuf) -> Uv {
+    let uv = Uv::new(None, false).await.expect("Uv::new failed");
+    let env_vars: HashMap<String, String> = HashMap::new();
+    let venv_child = uv.venv(cwd, &env_vars).await.expect("venv spawn failed");
+    let code = wait(venv_child).await;
+    assert_eq!(code, 0, "venv creation failed");
+    uv
+}
+
+#[tokio::test]
+async fn sync_succeeds_for_simple_requirements() {
+    let tmp = TempDir::new().expect("tempdir");
+    let cwd = tmp.path().to_path_buf();
+
+    tokio::fs::write(cwd.join("requirements.txt"), "six\n")
+        .await
+        .expect("write requirements.txt");
+
+    let uv = make_uv_with_venv(&cwd).await;
+    let env_vars: HashMap<String, String> = HashMap::new();
+    let child = uv.sync(&cwd, &env_vars).await.expect("sync spawn failed");
+    let code = wait(child).await;
+    assert_eq!(code, 0, "sync should succeed for a simple requirements.txt");
+}
+
+#[tokio::test]
+async fn sync_succeeds_when_user_requires_modern_setuptools() {
+    let tmp = TempDir::new().expect("tempdir");
+    let cwd = tmp.path().to_path_buf();
+
+    // Regression case: an app that requires setuptools>=82 used to fail
+    // because tower-uv unconditionally injected `setuptools<82`. Now the
+    // default sync path applies no pin, so resolution should succeed.
+    tokio::fs::write(cwd.join("requirements.txt"), "setuptools>=82\n")
+        .await
+        .expect("write requirements.txt");
+
+    let uv = make_uv_with_venv(&cwd).await;
+    let env_vars: HashMap<String, String> = HashMap::new();
+    let child = uv.sync(&cwd, &env_vars).await.expect("sync spawn failed");
+    let code = wait(child).await;
+    assert_eq!(
+        code, 0,
+        "sync should succeed when the user requires setuptools>=82"
+    );
+}
+
+#[tokio::test]
+async fn sync_with_legacy_setuptools_pin_installs_legacy_setuptools() {
+    let tmp = TempDir::new().expect("tempdir");
+    let cwd = tmp.path().to_path_buf();
+
+    tokio::fs::write(cwd.join("requirements.txt"), "six\n")
+        .await
+        .expect("write requirements.txt");
+
+    let uv = make_uv_with_venv(&cwd).await;
+    let env_vars: HashMap<String, String> = HashMap::new();
+    let child = uv
+        .sync_with_legacy_setuptools_pin(&cwd, &env_vars)
+        .await
+        .expect("retry spawn failed");
+    let code = wait(child).await;
+    assert_eq!(
+        code, 0,
+        "sync_with_legacy_setuptools_pin should succeed when the pin is compatible"
+    );
+}
+
+#[tokio::test]
+async fn sync_with_legacy_setuptools_pin_fails_when_user_requires_modern_setuptools() {
+    let tmp = TempDir::new().expect("tempdir");
+    let cwd = tmp.path().to_path_buf();
+
+    // The fallback method intentionally pins `setuptools<82`. When the user's
+    // requirements demand setuptools>=82, the resolver must report a conflict
+    // — this confirms the pin is actually being applied.
+    tokio::fs::write(cwd.join("requirements.txt"), "setuptools>=82\n")
+        .await
+        .expect("write requirements.txt");
+
+    let uv = make_uv_with_venv(&cwd).await;
+    let env_vars: HashMap<String, String> = HashMap::new();
+    let child = uv
+        .sync_with_legacy_setuptools_pin(&cwd, &env_vars)
+        .await
+        .expect("retry spawn failed");
+    let code = wait(child).await;
+    assert_ne!(
+        code, 0,
+        "sync_with_legacy_setuptools_pin should fail when the pin conflicts with user's requirements"
+    );
+}
+
+#[tokio::test]
+async fn sync_with_legacy_setuptools_pin_errors_without_requirements_txt() {
+    let tmp = TempDir::new().expect("tempdir");
+    let cwd = tmp.path().to_path_buf();
+
+    let uv = Uv::new(None, false).await.expect("Uv::new failed");
+    let env_vars: HashMap<String, String> = HashMap::new();
+    let result = uv.sync_with_legacy_setuptools_pin(&cwd, &env_vars).await;
+    assert!(
+        matches!(result, Err(tower_uv::Error::MissingPyprojectToml)),
+        "fallback should refuse to run without a requirements.txt"
+    );
+}