Fix cargo add overwriting symlinked Cargo.toml files

Author: RaghavenderSingh

src/cargo/util/toml_mut/manifest.rs

@@ -323,9 +323,16 @@ impl LocalManifest {
         };
         let new_contents_bytes = raw.as_bytes();
 
-        cargo_util::paths::write_atomic(&self.path, new_contents_bytes)
-    }
+        // Check if the path is a symlink and follow it if it is
+        let actual_path = if self.path.is_symlink() {
+            std::fs::read_link(&self.path)?
+        } else {
+            self.path.clone()
+        };
 
+        // Write to the actual target path instead of the symlink
+        cargo_util::paths::write_atomic(&actual_path, new_contents_bytes)
+    }
     /// Lookup a dependency.
     pub fn get_dependency_versions<'s>(
         &'s self,

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 std::fs;
+
+#[cargo_test]
+fn preserve_symlink_to_cargo_toml() {
+    if !cargo_test_support::symlink_supported() {
+        return;
+    }
+
+    let project = project().file("src/lib.rs", "").build();
+
+    let target_dir = project.root().join("target_dir");
+    fs::create_dir_all(&target_dir).unwrap();
+
+    // Create the target Cargo.toml
+    fs::copy(
+        project.root().join("Cargo.toml"),
+        target_dir.join("Cargo.toml"),
+    )
+    .unwrap();
+
+    // Remove the original and create a symlink
+    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();
+    }
+
+    // Add a dependency
+    project.cargo("add rand").run();
+
+    // Verify the symlink is preserved
+    assert!(project.root().join("Cargo.toml").is_symlink());
+}