Tracking Removed Features in Rust Crates: A Practical Guide

Rust crate maintainers frequently update their libraries, sometimes adding new features and other times removing or deprecating existing ones. If you’ve ever encountered an error like this:

error[E0432]: unresolved import `server_fn::server`
 --> src/main.rs:4:17
  |
4 | use server_fn::{server, ServerFnError};
  |                 ^^^^^^
  |                 no `server` in the root

You’re not alone. Features can disappear between versions, and figuring out why can be tricky. In this guide, I’ll walk you through how to track removed features in Rust crates and find alternatives when necessary.

1️⃣ Check the Crate’s Documentation on Docs.rs

Most Rust libraries have auto-generated documentation on docs.rs. If a feature was available in a previous version but is now missing, comparing different versions of the docs can help.

🔍 Steps to Check:

• Open the latest documentation:
  👉 https://docs.rs/server_fn/latest/server_fn
• Compare it with an older version by replacing latest with a specific version:
  👉 https://docs.rs/server_fn/0.5/server_fn

🧐 What to Look For?

• If the macro/function is missing in the latest version.
• Any deprecation warnings or migration notes.

2️⃣ Read the Crate’s Changelog (CHANGELOG.md)

Many Rust projects maintain a changelog that lists feature additions, removals, and breaking changes.

🔍 Where to Find It?

• Check the crate’s GitHub repository (if available). Example: 👉 https://github.com/DioxusLabs/server_fn/blob/main/CHANGELOG.md
• Look for entries like:

## [0.6.0] - 2024-02-10
- Removed `#[server]` macro in favor of `#[new_macro]`

🧐 What to Look For?

• Any mention of removals or breaking changes.
• Suggested replacements or migration paths.

3️⃣ Compare Cargo Versions in Your Project

If you suspect a feature was removed, you can downgrade to an older version and test.

🔍 Steps to Check:

1. Check which version is installed:

cargo tree | grep server_fn

2. Force an older version in Cargo.toml:

server_fn = "=0.5.0"

3. Clean and recompile:

cargo clean && cargo check

🧐 What to Look For?

If the feature works in an older version but not in the latest, it was likely removed.

4️⃣ Check GitHub Issues, Commits, and PRs

Developers often discuss feature removals in GitHub issues or pull requests.

🔍 Steps to Check:

1. Open the repository:
   👉 https://github.com/DioxusLabs/server_fn
2. Use GitHub’s search bar to look for:

• "#[server] removed"
• "breaking changes"
• "deprecated"

3. Browse the Issues and Pull Requests tabs.

👉 Example search:
https://github.com/DioxusLabs/server_fn/issues?q=server

🧐 What to Look For?

• Discussions about why the feature was removed.
• Suggestions for migration or alternatives.

5️⃣ Use 'cargo doc’ for Offline Documentation

If you’re working offline or want to check the currently installed version, you can generate local docs.

🔍 Steps to Check:

cargo doc --open

This will open your browser with the documentation for the exact version installed in your project.

🧐 What to Look For?

• Check if the feature is still documented.
• If missing, verify if it existed in older versions.

6️⃣ Use 'rustc --explain' for Missing Imports

If Rust can’t find a removed macro or function, it might suggest alternative solutions.

🔍 Steps to Check:

rustc --explain E0432

If #[server] was removed, Rust might suggest:

• Possible alternatives.
• Reasons why it no longer exists.

🚀 TL;DR — Quick Steps to Track Removed Feature

✅ Docs.rs → Compare old vs. new documentation
✅ CHANGELOG.md → Look for “Removed” or “Breaking Changes”
✅ Cargo.toml → Downgrade to an older version and test
✅ GitHub Issues → Search for discussions on feature removal
✅ Cargo Doc → Generate docs for installed version (cargo doc --open)
✅ Rustc Explain → Use rustc --explain for missing imports

🛠️ Want to Try It?

If you suspect #[server] was removed from server_fn, try:

cargo add server_fn@0.5
cargo check

Then compare with:

cargo add server_fn@latest
cargo check

🚀 If it works in an older version but not the new one, the feature was removed!

Final Thoughts

Rust’s ecosystem is constantly evolving, and features come and go. By using the strategies in this guide, you can quickly determine what happened to a missing feature and how to adapt your code.

💬 Have you ever struggled with a removed Rust feature? Share your experience in the comments! 👇