Compare version fields' equalities directly

Instead of creating another VersionReq, this can reduce some extra
efforts on version matching logic. Though it also may introduces
divergence from semver's matching logic. Accordingly, we borrow unit
tests from semver crate and compare the matching results to prevent
future breaks.

src/cargo/util/semver_ext.rs

@@ -82,7 +82,12 @@ impl OptVersionReq {
         match self {
             OptVersionReq::Any => true,
             OptVersionReq::Req(req) => req.matches(version),
-            OptVersionReq::Locked(v, _) => VersionReq::exact(v).matches(version),
+            OptVersionReq::Locked(v, _) => {
+                v.major == version.major
+                    && v.minor == version.minor
+                    && v.patch == version.patch
+                    && v.pre == version.pre
+            }
         }
     }
 }
@@ -102,3 +107,40 @@ impl From<VersionReq> for OptVersionReq {
         OptVersionReq::Req(req)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn locked_has_the_same_with_exact() {
+        fn test_versions(target_ver: &str, vers: &[&str]) {
+            let ver = Version::parse(target_ver).unwrap();
+            let exact = OptVersionReq::exact(&ver);
+            let mut locked = exact.clone();
+            locked.lock_to(&ver);
+            for v in vers {
+                let v = Version::parse(v).unwrap();
+                assert_eq!(exact.matches(&v), locked.matches(&v));
+            }
+        }
+
+        test_versions(
+            "1.0.0",
+            &["1.0.0", "1.0.1", "0.9.9", "0.10.0", "0.1.0", "1.0.0-pre"],
+        );
+        test_versions("0.9.0", &["0.9.0", "0.9.1", "1.9.0", "0.0.9", "0.9.0-pre"]);
+        test_versions("0.0.2", &["0.0.2", "0.0.1", "0.0.3", "0.0.2-pre"]);
+        test_versions(
+            "0.1.0-beta2.a",
+            &[
+                "0.1.0-beta2.a",
+                "0.9.1",
+                "0.1.0",
+                "0.1.1-beta2.a",
+                "0.1.0-beta2",
+            ],
+        );
+        test_versions("0.1.0+meta", &["0.1.0", "0.1.0+meta", "0.1.0+any"]);
+    }
+}