Do not call it "Downgrading" when difference is only build metadata

Author: dtolnay

src/cargo/ops/cargo_generate_lockfile.rs

@@ -152,7 +152,15 @@ pub fn update_lockfile(ws: &Workspace<'_>, opts: &UpdateOptions<'_>) -> CargoRes
                 format!("{} -> v{}", removed[0], added[0].version())
             };
 
-            if removed[0].version() > added[0].version() {
+            // If versions differ only in build metadata, we call it an "update"
+            // regardless of whether the build metadata has gone up or down.
+            // This metadata is often stuff like git commit hashes, which are
+            // not meaningfully ordered.
+            let removed = removed[0].version();
+            let added = added[0].version();
+            if (removed.major, removed.minor, removed.patch, &removed.pre)
+                > (added.major, added.minor, added.patch, &added.pre)
+            {
                 print_change("Downgrading", msg, &style::WARN)?;
             } else {
                 print_change("Updating", msg, &style::GOOD)?;

tests/testsuite/update.rs

@@ -423,11 +423,13 @@ fn update_precise_build_metadata() {
         )
         .run();
 
+    // This is not considered "Downgrading". Build metadata are not assumed to
+    // be ordered.
     p.cargo("update serde --precise 0.0.1+first")
         .with_stderr(
             "\
 [UPDATING] `[..]` index
-[DOWNGRADING] serde v0.0.1+second -> v0.0.1+first
+[UPDATING] serde v0.0.1+second -> v0.0.1+first
 ",
         )
         .run();