fix: fix hang by preventing stream.buffered(0) in concurrent downloads

Author: rami3l

src/cli/rustup_mode.rs

@@ -806,7 +806,7 @@ async fn check_updates(cfg: &Cfg<'_>, opts: CheckOpts) -> Result<utils::ExitCode
 
     // Ensure that `.buffered()` is never called with 0 as this will cause a hang.
     // See: https://github.com/rust-lang/futures-rs/pull/1194#discussion_r209501774
-    if num_channels > 0 {
+    if channels_len > 0 {
         let multi_progress_bars =
             MultiProgress::with_draw_target(cfg.process.progress_draw_target());
         let semaphore = Arc::new(Semaphore::new(num_channels));

src/dist/manifestation.rs

@@ -200,7 +200,7 @@ impl Manifestation {
                     .await
                 }
             });
-        if num_channels > 0 {
+        if components_len > 0 {
             let results = component_stream
                 .buffered(components_len)
                 .collect::<Vec<_>>()

src/dist/manifestation/tests.rs

@@ -1313,6 +1313,33 @@ async fn remove_extensions_does_not_remove_other_components() {
     assert!(utils::path_exists(cx.prefix.path().join("bin/rustc")));
 }
 
+#[tokio::test]
+async fn remove_extensions_does_not_hang_with_concurrent_downloads_override() {
+    let cx = TestContext::with_env(
+        None,
+        GZOnly,
+        [("RUSTUP_CONCURRENT_DOWNLOADS".to_owned(), "2".to_owned())].into(),
+    );
+
+    let adds = vec![Component::new(
+        "rust-std".to_string(),
+        Some(TargetTriple::new("i686-apple-darwin")),
+        false,
+    )];
+
+    cx.update_from_dist(&adds, &[], false).await.unwrap();
+
+    let removes = vec![Component::new(
+        "rust-std".to_string(),
+        Some(TargetTriple::new("i686-apple-darwin")),
+        false,
+    )];
+
+    cx.update_from_dist(&[], &removes, false).await.unwrap();
+
+    assert!(utils::path_exists(cx.prefix.path().join("bin/rustc")));
+}
+
 #[tokio::test]
 async fn add_and_remove_for_upgrade() {
     let cx = TestContext::new(None, GZOnly);

tests/suite/cli_inst_interactive.rs

@@ -262,6 +262,43 @@ no active toolchain
         .is_ok();
 }
 
+#[tokio::test]
+async fn with_no_toolchain_doesnt_hang() {
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+    run_input(
+        &cx.config,
+        &[
+            "rustup-init",
+            "--no-modify-path",
+            "--default-toolchain=none",
+        ],
+        "\n\n",
+    )
+    .is_ok();
+
+    cx.config.expect(["rustup", "check"]).await.is_err();
+}
+
+#[tokio::test]
+async fn with_no_toolchain_doesnt_hang_with_concurrent_downloads_override() {
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+    run_input(
+        &cx.config,
+        &[
+            "rustup-init",
+            "--no-modify-path",
+            "--default-toolchain=none",
+        ],
+        "\n\n",
+    )
+    .is_ok();
+
+    cx.config
+        .expect_with_env(["rustup", "check"], [("RUSTUP_CONCURRENT_DOWNLOADS", "2")])
+        .await
+        .is_err();
+}
+
 #[tokio::test]
 async fn with_non_default_toolchain_still_prompts() {
     let cx = CliTestContext::new(Scenario::SimpleV2).await;