Run a parallel pre-check before updating toolchains

src/cli/common.rs

@@ -10,6 +10,7 @@ use std::{cmp, env};
 use anstyle::Style;
 use anyhow::{Context, Result, anyhow};
 use clap_cargo::style::{CONTEXT, ERROR, UPDATE_ADDED, UPDATE_UNCHANGED, UPDATE_UPGRADED};
+use futures_util::future::join_all;
 use git_testament::{git_testament, render_testament};
 use tracing::{error, info, warn};
 use tracing_subscriber::{EnvFilter, Registry, reload::Handle};
@@ -213,11 +214,29 @@ fn show_channel_updates(
 
 pub(crate) async fn update_all_channels(cfg: &Cfg<'_>, force_update: bool) -> Result<ExitCode> {
     let profile = cfg.get_profile()?;
+    let channels = cfg.list_channels()?;
+
+    // Run a pre-check to determine which channels have updates available.
+    // This step is skipped when force-updating.
+    let needs_update = if force_update {
+        vec![true; channels.len()]
+    } else {
+        join_all(channels.iter().map(|(_, d)| d.show_dist_version()))
+            .await
+            .into_iter()
+            .map(|v| v.map_or(true, |opt| opt.is_some()))
+            .collect()
+    };
+
     let mut toolchains = Vec::new();
-    for (desc, distributable) in cfg.list_channels()? {
-        let options = DistOptions::new(&[], &[], &desc, profile, force_update, cfg)?
-            .for_update(&distributable, false);
-        let result = InstallMethod::Dist(options).install().await;
+    for ((desc, distributable), needs) in channels.into_iter().zip(needs_update) {
+        let result = if needs {
+            let options = DistOptions::new(&[], &[], &desc, profile, force_update, cfg)?
+                .for_update(&distributable, false);
+            InstallMethod::Dist(options).install().await
+        } else {
+            Ok(UpdateStatus::Unchanged)
+        };
 
         if let Err(e) = &result {
             error!("{e}");

tests/suite/cli_rustup.rs

@@ -97,7 +97,6 @@ async fn rustup_stable_no_change() {
 
 "#]])
         .with_stderr(snapbox::str![[r#"
-info: syncing channel updates for stable-[HOST_TRIPLE]
 info: cleaning up downloads & tmp directories
 
 "#]])
@@ -210,7 +209,6 @@ info: syncing channel updates for stable-[HOST_TRIPLE]
 info: latest update on 2015-01-02 for version 1.1.0 (hash-stable-1.1.0)
 info: removing previous version of component cargo
 ...
-info: syncing channel updates for beta-[HOST_TRIPLE]
 info: syncing channel updates for nightly-[HOST_TRIPLE]
 info: latest update on 2015-01-02 for version 1.3.0 (hash-nightly-2)
 info: removing previous version of component cargo

tests/suite/cli_self_upd.rs

@@ -690,7 +690,6 @@ async fn rustup_self_update_exact() {
 
 "#]])
         .with_stderr(snapbox::str![[r#"
-info: syncing channel updates for stable-[HOST_TRIPLE]
 info: checking for self-update (current version: [CURRENT_VERSION])
 info: downloading self-update (new version: [TEST_VERSION])
 info: cleaning up downloads & tmp directories