Fix disagreement about lockfile ordering on stable/nightly

src/cargo/core/source/source_id.rs

@@ -44,8 +44,9 @@ struct SourceIdInner {
 /// source.
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 enum SourceKind {
-    /// A git repository.
-    Git(GitReference),
+    // Note that the ordering here is important for how it affects the `Ord`
+    // implementation, notably how this affects the ordering of serialized
+    // packages into lock files.
     /// A local path..
     Path,
     /// A remote registry.
@@ -54,6 +55,8 @@ enum SourceKind {
     LocalRegistry,
     /// A directory-based registry.
     Directory,
+    /// A git repository.
+    Git(GitReference),
 }
 
 /// Information to find a specific commit in a Git repository.

tests/testsuite/lockfile_compat.rs

@@ -771,3 +771,75 @@ dependencies = [
 
     p.cargo("build --locked").run();
 }
+
+#[cargo_test]
+fn same_name_version_different_sources() {
+    let cksum = Package::new("foo", "0.1.0").publish();
+    let (git_project, repo) = git::new_repo("dep1", |project| {
+        project
+            .file(
+                "Cargo.toml",
+                r#"
+                    [project]
+                    name = "foo"
+                    version = "0.1.0"
+                "#,
+            )
+            .file("src/lib.rs", "")
+    });
+    let head_id = repo.head().unwrap().target().unwrap();
+
+    // Lockfile was generated with Rust 1.51
+    let lockfile = format!(
+        r#"# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "foo"
+version = "0.1.0"
+dependencies = [
+ "foo 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "foo 0.1.0 (git+{url})",
+]
+
+[[package]]
+name = "foo"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "{cksum}"
+
+[[package]]
+name = "foo"
+version = "0.1.0"
+source = "git+{url}#{sha}"
+"#,
+        sha = head_id,
+        url = git_project.url(),
+        cksum = cksum
+    );
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            &format!(
+                r#"
+                    [project]
+                    name = "foo"
+                    version = "0.1.0"
+
+                    [dependencies]
+                    foo = "0.1.0"
+                    foo2 = {{ git = '{}', package = 'foo' }}
+                "#,
+                git_project.url(),
+            ),
+        )
+        .file("src/lib.rs", "")
+        .file("Cargo.lock", &lockfile)
+        .build();
+
+    p.cargo("build").run();
+
+    assert_eq!(p.read_file("Cargo.lock"), lockfile);
+}