dist: Trim the manifest toml to improve startup time

Signed-off-by: Daniel Silverstone <dsilvers@digital-scurf.org>

src/dist/dist.rs

@@ -714,12 +714,15 @@ fn try_update_from_dist_<'a>(
         },
         toolchain,
     ) {
-        Ok(Some((m, hash))) => {
+        Ok(Some((mut m, hash))) => {
             (download.notify_handler)(Notification::DownloadedManifest(
                 &m.date,
                 m.get_rust_version().ok(),
             ));
 
+            m.trim(&toolchain.target);
+            m.validate()?;
+
             let profile_components = match profile {
                 Some(profile) => m.get_profile_components(profile, &toolchain.target)?,
                 None => Vec::new(),

src/dist/manifest.rs

@@ -284,7 +284,7 @@ impl Manifest {
         Ok(())
     }
 
-    fn validate(&self) -> Result<()> {
+    pub fn validate(&self) -> Result<()> {
         // Every component mentioned must have an actual package to download
         for pkg in self.packages.values() {
             match pkg.targets {
@@ -319,6 +319,34 @@ impl Manifest {
             c
         })
     }
+
+    /// Trim the manifest so that it is only relevant for the given toolchain
+    /// target.  This massively reduces the work rustup has to do to parse the
+    /// channel manifests in future
+    pub fn trim(&mut self, target: &TargetTriple) {
+        for (pname, package) in self.packages.iter_mut() {
+            if pname == "rust-std" {
+                // We retain all targets for rust-std since that gives us our
+                // rustup target add ...
+                continue;
+            }
+            match package.targets {
+                PackageTargets::Wildcard(_) => {}
+                PackageTargets::Targeted(ref mut targs) => {
+                    targs.retain(|k, _| k == target);
+                    for (_, pkg) in targs.iter_mut() {
+                        pkg.components.retain(|comp| {
+                            // Components of packages are retained only if they
+                            // are rust-std (for targets) or if their target is
+                            // either wildcarded, or matches the goal target.
+                            comp.pkg.as_str() == "rust-std"
+                                || comp.target.as_ref().map(|t| t == target).unwrap_or(true)
+                        })
+                    }
+                }
+            }
+        }
+    }
 }
 
 impl Package {