Fix fetching git repos after a force push.

src/cargo/sources/git/utils.rs

@@ -785,29 +785,32 @@ pub fn fetch(
     // which need to get fetched. Additionally record if we're fetching tags.
     let mut refspecs = Vec::new();
     let mut tags = false;
+    // The `+` symbol on the refspec means to allow a forced (fast-forward)
+    // update which is needed if there is ever a force push that requires a
+    // fast-forward.
     match reference {
         // For branches and tags we can fetch simply one reference and copy it
         // locally, no need to fetch other branches/tags.
         GitReference::Branch(b) => {
-            refspecs.push(format!("refs/heads/{0}:refs/remotes/origin/{0}", b));
+            refspecs.push(format!("+refs/heads/{0}:refs/remotes/origin/{0}", b));
         }
         GitReference::Tag(t) => {
-            refspecs.push(format!("refs/tags/{0}:refs/remotes/origin/tags/{0}", t));
+            refspecs.push(format!("+refs/tags/{0}:refs/remotes/origin/tags/{0}", t));
         }
 
         GitReference::DefaultBranch => {
-            refspecs.push(String::from("HEAD:refs/remotes/origin/HEAD"));
+            refspecs.push(String::from("+HEAD:refs/remotes/origin/HEAD"));
         }
 
         GitReference::Rev(rev) => {
             if rev.starts_with("refs/") {
-                refspecs.push(format!("{0}:{0}", rev));
+                refspecs.push(format!("+{0}:{0}", rev));
             } else {
                 // We don't know what the rev will point to. To handle this
                 // situation we fetch all branches and tags, and then we pray
                 // it's somewhere in there.
-                refspecs.push(String::from("refs/heads/*:refs/remotes/origin/*"));
-                refspecs.push(String::from("HEAD:refs/remotes/origin/HEAD"));
+                refspecs.push(String::from("+refs/heads/*:refs/remotes/origin/*"));
+                refspecs.push(String::from("+HEAD:refs/remotes/origin/HEAD"));
                 tags = true;
             }
         }

tests/testsuite/git.rs

@@ -3282,3 +3282,105 @@ fn metadata_master_consistency() {
     let bar_source = format!("git+{}", git_project.url());
     p.cargo("metadata").with_json(&metadata(&bar_source)).run();
 }
+
+#[cargo_test]
+fn git_with_force_push() {
+    // Checks that cargo can handle force-pushes to git repos.
+    // This works by having a git dependency that is updated with an amend
+    // commit, and tries with various forms (default branch, branch, rev,
+    // tag).
+    let main = |text| format!(r#"pub fn f() {{ println!("{}"); }}"#, text);
+    let (git_project, repo) = git::new_repo("dep1", |project| {
+        project
+            .file("Cargo.toml", &basic_lib_manifest("dep1"))
+            .file("src/lib.rs", &main("one"))
+    });
+    let manifest = |extra| {
+        format!(
+            r#"
+                [project]
+                name = "foo"
+                version = "0.0.1"
+                edition = "2018"
+
+                [dependencies]
+                dep1 = {{ git = "{}"{} }}
+            "#,
+            git_project.url(),
+            extra
+        )
+    };
+    let p = project()
+        .file("Cargo.toml", &manifest(""))
+        .file("src/main.rs", "fn main() { dep1::f(); }")
+        .build();
+    // Download the original and make sure it is OK.
+    p.cargo("build").run();
+    p.rename_run("foo", "foo1").with_stdout("one").run();
+
+    let find_head = || t!(t!(repo.head()).peel_to_commit());
+
+    let amend_commit = |text| {
+        // commit --amend a change that will require a force fetch.
+        git_project.change_file("src/lib.rs", &main(text));
+        git::add(&repo);
+        let commit = find_head();
+        let tree_id = t!(t!(repo.index()).write_tree());
+        t!(commit.amend(
+            Some("HEAD"),
+            None,
+            None,
+            None,
+            None,
+            Some(&t!(repo.find_tree(tree_id)))
+        ));
+    };
+
+    let mut rename_annoyance = 1;
+
+    let mut verify = |text: &str| {
+        // Perform the fetch.
+        p.cargo("update").run();
+        p.cargo("build").run();
+        rename_annoyance += 1;
+        p.rename_run("foo", &format!("foo{}", rename_annoyance))
+            .with_stdout(text)
+            .run();
+    };
+
+    amend_commit("two");
+    verify("two");
+
+    // Try with a rev.
+    let head1 = find_head().id().to_string();
+    let extra = format!(", rev = \"{}\"", head1);
+    p.change_file("Cargo.toml", &manifest(&extra));
+    verify("two");
+    amend_commit("three");
+    let head2 = find_head().id().to_string();
+    assert_ne!(&head1, &head2);
+    let extra = format!(", rev = \"{}\"", head2);
+    p.change_file("Cargo.toml", &manifest(&extra));
+    verify("three");
+
+    // Try with a tag.
+    git::tag(&repo, "my-tag");
+    p.change_file("Cargo.toml", &manifest(", tag = \"my-tag\""));
+    verify("three");
+    amend_commit("tag-three");
+    let head = t!(t!(repo.head()).peel(git2::ObjectType::Commit));
+    t!(repo.tag("my-tag", &head, &t!(repo.signature()), "move tag", true));
+    verify("tag-three");
+
+    // Try with a branch.
+    let br = t!(repo.branch("awesome-stuff", &find_head(), false));
+    t!(repo.checkout_tree(&t!(br.get().peel(git2::ObjectType::Tree)), None));
+    t!(repo.set_head("refs/heads/awesome-stuff"));
+    git_project.change_file("src/lib.rs", &main("awesome-three"));
+    git::add(&repo);
+    git::commit(&repo);
+    p.change_file("Cargo.toml", &manifest(", branch = \"awesome-stuff\""));
+    verify("awesome-three");
+    amend_commit("awesome-four");
+    verify("awesome-four");
+}