test: Add failing test for cargo add breaking symlinks

Author: RaghavenderSingh

tests/testsuite/cargo_add/mod.rs

@@ -145,6 +145,7 @@ mod script_bare;
 mod script_frontmatter;
 mod script_shebang;
 mod sorted_table_with_dotted_item;
+mod symlink;
 mod target;
 mod target_cfg;
 mod unknown_inherited_feature;

tests/testsuite/cargo_add/symlink.rs

@@ -0,0 +1,51 @@
+use cargo_test_support::prelude::*;
+use cargo_test_support::project;
+use cargo_test_support::registry;
+use std::fs;
+
+#[cargo_test]
+fn symlink_case() {
+    if !cargo_test_support::symlink_supported() {
+        return;
+    }
+
+    registry::init();
+    registry::Package::new("test-dep", "1.0.0").publish();
+
+    let project = project().file("src/lib.rs", "").build();
+
+    let target_dir = project.root().join("target_dir");
+    fs::create_dir_all(&target_dir).unwrap();
+
+    fs::copy(
+        project.root().join("Cargo.toml"),
+        target_dir.join("Cargo.toml"),
+    )
+    .unwrap();
+
+    fs::remove_file(project.root().join("Cargo.toml")).unwrap();
+
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::symlink;
+        symlink(
+            target_dir.join("Cargo.toml"),
+            project.root().join("Cargo.toml"),
+        )
+        .unwrap();
+    }
+
+    #[cfg(windows)]
+    {
+        use std::os::windows::fs::symlink_file;
+        symlink_file(
+            target_dir.join("Cargo.toml"),
+            project.root().join("Cargo.toml"),
+        )
+        .unwrap();
+    }
+
+    project.cargo("add test-dep").run();
+
+    assert!(project.root().join("Cargo.toml").is_symlink());
+}