Auto merge of #12796 - dtolnay-contrib:switching, r=epage

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

### What does this PR try to resolve?

When a `cargo update --precise` changes a dependency between 2 versions which differ only in build metadata, Cargo prints a log referring to it as "Updating" or "Downgrading" the dependency, depending on a comparison between the build metadatas.

This is usually not meaningful, given that build metadata is often stuff like git commit hashes, which are not meaningfully ordered.

```console
    Updating crates.io index
 Downgrading foo v0.0.1+43ef4fe -> v0.0.1+2c65d16
    Updating bar v0.0.2+bc17664 -> v0.0.2+c144a98
```

~~This PR changes to the word "Switching" when the version major, minor, patch, and pre-release value are not being changed.~~
This PR uses the word "Updating" when the version major, minor, patch, and pre-release value are unchanged, regardless of whether the build metadata is going up or down.

### How should we test and review this PR?

- `cargo test`
- `cargo build --release`
- `/path/to/cargo/target/release/cargo add tonic_datastore_v1`
- `/path/to/cargo/target/release/cargo update -p tonic_datastore_v1 --precise 0.1.0+3562b6cb3`
- `/path/to/cargo/target/release/cargo update -p tonic_datastore_v1 --precise 0.1.0+ee9e8e4e6`

Before:
<img src="https://github.com/rust-lang/cargo/assets/1940490/93e377e7-928e-4cec-aff6-451166ef7c81" width="500">

~~After:~~
<img src="https://github.com/rust-lang/cargo/assets/1940490/bb71459e-469a-4e09-bb8a-4083f34bce79" width="500">

After:
<img src="https://github.com/rust-lang/cargo/assets/1940490/8804e2fe-d0de-4c9e-b463-a5742daf9446" width="500">

Cargo.toml

@@ -76,7 +76,7 @@ rand = "0.8.5"
 rustfix = "0.6.1"
 same-file = "1.0.6"
 security-framework = "2.9.2"
-semver = { version = "1.0.19", features = ["serde"] }
+semver = { version = "1.0.20", features = ["serde"] }
 serde = "1.0.188"
 serde-untagged = "0.1.1"
 serde-value = "0.7.0"

src/cargo/core/package_id.rs

@@ -29,8 +29,7 @@ struct PackageIdInner {
     source_id: SourceId,
 }
 
-// Custom equality that uses full equality of SourceId, rather than its custom equality,
-// and Version, which usually ignores `build` metadata.
+// Custom equality that uses full equality of SourceId, rather than its custom equality.
 //
 // The `build` part of the version is usually ignored (like a "comment").
 // However, there are some cases where it is important. The download path from
@@ -40,11 +39,7 @@ struct PackageIdInner {
 impl PartialEq for PackageIdInner {
     fn eq(&self, other: &Self) -> bool {
         self.name == other.name
-            && self.version.major == other.version.major
-            && self.version.minor == other.version.minor
-            && self.version.patch == other.version.patch
-            && self.version.pre == other.version.pre
-            && self.version.build == other.version.build
+            && self.version == other.version
             && self.source_id.full_eq(other.source_id)
     }
 }
@@ -53,11 +48,7 @@ impl PartialEq for PackageIdInner {
 impl Hash for PackageIdInner {
     fn hash<S: hash::Hasher>(&self, into: &mut S) {
         self.name.hash(into);
-        self.version.major.hash(into);
-        self.version.minor.hash(into);
-        self.version.patch.hash(into);
-        self.version.pre.hash(into);
-        self.version.build.hash(into);
+        self.version.hash(into);
         self.source_id.full_hash(into);
     }
 }
@@ -237,6 +228,16 @@ impl fmt::Debug for PackageId {
     }
 }
 
+impl fmt::Debug for PackageIdInner {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PackageIdInner")
+            .field("name", &self.name)
+            .field("version", &self.version.to_string())
+            .field("source", &self.source_id.to_string())
+            .finish()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::PackageId;
@@ -261,4 +262,14 @@ mod tests {
         let pkg_id = PackageId::new("foo", "1.0.0", SourceId::for_registry(&loc).unwrap()).unwrap();
         assert_eq!("foo v1.0.0", pkg_id.to_string());
     }
+
+    #[test]
+    fn unequal_build_metadata() {
+        let loc = CRATES_IO_INDEX.into_url().unwrap();
+        let repo = SourceId::for_registry(&loc).unwrap();
+        let first = PackageId::new("foo", "0.0.1+first", repo).unwrap();
+        let second = PackageId::new("foo", "0.0.1+second", repo).unwrap();
+        assert_ne!(first, second);
+        assert_ne!(first.inner, second.inner);
+    }
 }

src/cargo/ops/cargo_generate_lockfile.rs

@@ -8,6 +8,7 @@ use crate::util::config::Config;
 use crate::util::style;
 use crate::util::CargoResult;
 use anstyle::Style;
+use std::cmp::Ordering;
 use std::collections::{BTreeMap, HashSet};
 use tracing::debug;
 
@@ -152,7 +153,11 @@ 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.
+            if removed[0].version().cmp_precedence(added[0].version()) == Ordering::Greater {
                 print_change("Downgrading", msg, &style::WARN)?;
             } else {
                 print_change("Updating", msg, &style::GOOD)?;

src/cargo/sources/registry/index.rs

@@ -98,6 +98,7 @@ use cargo_util::{paths, registry::make_dep_path};
 use semver::Version;
 use serde::Deserialize;
 use std::borrow::Cow;
+use std::cmp::Ordering;
 use std::collections::BTreeMap;
 use std::collections::{HashMap, HashSet};
 use std::fs;
@@ -674,11 +675,8 @@ impl<'cfg> RegistryIndex<'cfg> {
                         (true, true) => s_vers == requested,
                         (true, false) => false,
                         (false, true) => {
-                            // Strip out the metadata.
-                            s_vers.major == requested.major
-                                && s_vers.minor == requested.minor
-                                && s_vers.patch == requested.patch
-                                && s_vers.pre == requested.pre
+                            // Compare disregarding the metadata.
+                            s_vers.cmp_precedence(requested) == Ordering::Equal
                         }
                         (false, false) => s_vers == requested,
                     }

src/cargo/util/semver_ext.rs

@@ -1,5 +1,6 @@
 use semver::{Comparator, Op, Version, VersionReq};
 use serde_untagged::UntaggedEnumVisitor;
+use std::cmp::Ordering;
 use std::fmt::{self, Display};
 
 #[derive(PartialEq, Eq, Hash, Clone, Debug)]
@@ -83,12 +84,7 @@ impl OptVersionReq {
         match self {
             OptVersionReq::Any => true,
             OptVersionReq::Req(req) => req.matches(version),
-            OptVersionReq::Locked(v, _) => {
-                v.major == version.major
-                    && v.minor == version.minor
-                    && v.patch == version.patch
-                    && v.pre == version.pre
-            }
+            OptVersionReq::Locked(v, _) => v.cmp_precedence(version) == Ordering::Equal,
         }
     }
 }

tests/testsuite/update.rs

@@ -391,6 +391,50 @@ fn update_precise() {
         .run();
 }
 
+#[cargo_test]
+fn update_precise_build_metadata() {
+    Package::new("serde", "0.0.1+first").publish();
+    Package::new("serde", "0.0.1+second").publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.0.0"
+
+                [dependencies]
+                serde = "0.0.1"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("generate-lockfile").run();
+    p.cargo("update serde --precise 0.0.1+first").run();
+
+    p.cargo("update serde --precise 0.0.1+second")
+        .with_stderr(
+            "\
+[UPDATING] `[..]` index
+[UPDATING] serde v0.0.1+first -> v0.0.1+second
+",
+        )
+        .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
+[UPDATING] serde v0.0.1+second -> v0.0.1+first
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn update_precise_do_not_force_update_deps() {
     Package::new("log", "0.1.0").publish();