tool_box! fails if tools cant be in separate files

[milesj]

Describe the bug

I have a handful of tools and keeping them all in the same file is growing unwieldy. I tried moving them to separate files, but when I call tool_box!, it fails with:

cannot define inherent `impl` for foreign type

What are you using rust-mcp-sdk for?
Select all that apply:

• Developing a MCP Server
• Developing a MCP Client

Technical details:

• rust-mcp-sdk Version : 0.4.5
• Cargo features enabled for rust-mcp-sdk : macros, server, 2025_03_26
• Environment/OS (Mac, Linux, Windows, etc) : macos

To Reproduce
Steps to reproduce the behavior:

1. ....
2. ....
3. ....

Expected behavior

Screenshots

Additional context

[milesj]

Actually, got this working by switching from * to explicit names for imports. I'm honestly kind of surprised star import didn't resolve the types here.

[hashemix]

Thanks @milesj for reporting this , and glad it is resolved!

We cannot directly use tools::* like that inside a macro call , as macro_rules!() expects explicit idents so following does not work:

tool_box!(FileSystemTools, tools::*); //❌ cannot define inherent `impl` for foreign type

But we can still import with * and pass them explicitly tho:

use tools::*
tool_box!( FileSystemTools, [ ReadFileTool, CreateDirectoryTool, DirectoryTreeTool] );

just in case it may help your case or others, here is how I organized multiple tools in rust-mcp-filesystem this way:

1- All tools and logics are under tools:: module as separate files: https://github.com/rust-mcp-stack/rust-mcp-filesystem/tree/main/src/tools

2- I call the tool_box!() on all of them in tools module: tools.rs

[milesj]

@hashemix I was actually doing something like this:

use crate:tools::*;

tool_box!(MoonTools, [SomeTool]);

But that didn't work. This did:

use crate:tools::SomeTool;

tool_box!(MoonTools, [SomeTool]);

I also noticed that trailing commas and comments in the array does not work either.

tool_box!(
    MoonTools,
    [
        GetProjectTool,
        GetProjectsTool,
        GetTaskTool,
        GetTasksTool,
        GetTouchedFiles,
        SyncWorkspaceTool # here
    ]
);

[hashemix]

@hashemix I was actually doing something like this:

use crate:tools::*;

tool_box!(MoonTools, [SomeTool]);

But that didn't work. This did:

use crate:tools::SomeTool;

tool_box!(MoonTools, [SomeTool]);

Thanks for the details, I was not able to reproduce that in a test project, will try to re-produce on the moon repo :)

And thanks for reporting the issue with the trailing comma, that one easy , wil update the macro to tolerate that 👍

[hashemix]

Interestingly having a trailing comma causes the exact same error : cannot define inherent impl for foreign type (rust-analyzer E0210).

Maybe that was the root cause in the first place, not the use crate:tools::*;

[milesj]

Ah yeah maybe it was. I went through many attempts.

[hashemix]

✔ fixed in v0.4.6