cargo vendor: Don't delete hidden top-level files.

src/cargo/ops/vendor.rs

@@ -80,7 +80,13 @@ fn sync(
     if !opts.no_delete {
         for entry in canonical_destination.read_dir()? {
             let entry = entry?;
-            to_remove.insert(entry.path());
+            if !entry
+                .file_name()
+                .to_str()
+                .map_or(false, |s| s.starts_with('.'))
+            {
+                to_remove.insert(entry.path());
+            }
         }
     }
 

tests/testsuite/vendor.rs

@@ -501,3 +501,39 @@ fn depend_on_vendor_dir_not_deleted() {
     p.cargo("vendor --respect-source-config").run();
     assert!(p.root().join("vendor/libc").is_dir());
 }
+
+#[cargo_test]
+fn ignore_hidden() {
+    // Don't delete files starting with `.`
+    Package::new("bar", "0.1.0").publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "1.0.0"
+            [dependencies]
+            bar = "0.1.0"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+    p.cargo("vendor --respect-source-config").run();
+    // Add a `.git` directory.
+    let repo = git::init(&p.root().join("vendor"));
+    git::add(&repo);
+    git::commit(&repo);
+    assert!(p.root().join("vendor/.git").exists());
+    // Vendor again, shouldn't change anything.
+    p.cargo("vendor --respect-source-config").run();
+    // .git should not be removed.
+    assert!(p.root().join("vendor/.git").exists());
+    // And just for good measure, make sure no files changed.
+    let mut opts = git2::StatusOptions::new();
+    assert!(repo
+        .statuses(Some(&mut opts))
+        .unwrap()
+        .iter()
+        .all(|status| status.status() == git2::Status::CURRENT));
+}