Signature help does not show anything.

[iampi31415]

Checked other resources

• This is not a bug report or feature request (Please use issues for those).
• This is a question about rustaceanvim, not rust-analyzer or Neovim.
• This is not a question about autocompletion.
• I have read the README.
• I have read the FAQ.
• I have searched for a solution using :h rustaceanvim.
• I have searched existing discussions.
• I have searched the existing issues/discussions of other plugins related to this question (if applicable).
• I have searched the existing rust-analyzer discussions (if applicable).
• I have added a very descriptive title to this question.

Description

Trying to get the signature help of a function. Works with K (but that's full docs), does not with gK. I tried with Ctrl-S as well, just in case, but nothing is shown either.

Hard for me to know whether this could be rust-analyzer's issue, etc. But I did try the minimal steps listed below.

Example Code

1. curl the minimal config:

curl https://raw.githubusercontent.com/mrcjkb/rustaceanvim/refs/heads/master/troubleshooting/minimal.lua -o minimal.lua

2. Start neovim `nvim -u minimal.lua`
3. Try to get a signature help, is it possible?

Neovim version (nvim -v)

NVIM v0.11.3
Build type: Release
LuaJIT 2.1.1748459687

Operating system/version

MacOS Sonoma

Output of :checkhealth rustaceanvim

==============================================================================
rustaceanvim:                                                             1 ⚠️

Checking for Lua dependencies ~
- ✅ OK optional dependency nvim-dap not installed. Needed for debugging features [mfussenegger/nvim-dap](https://github.com/mfussenegger/nvim-dap)

Checking external dependencies ~
- ✅ OK rust-analyzer: found rust-analyzer 1.89.0 (29483883 2025-08-04)
- ✅ OK Cargo: found cargo 1.89.0 (c24e10642 2025-06-23)
- ✅ OK rustc: found rustc 1.89.0 (29483883e 2025-08-04)

Checking config ~
- ✅ OK No errors found in config.

Checking for conflicting plugins ~
- ✅ OK No conflicting plugins detected.

Checking for tree-sitter parser ~
- ⚠️ WARNING No tree-sitter parser for Rust detected. Required by 'Rustc unpretty' command.

[mrcjkb]

Hey 👋

Signature help is typically implemented by a completion plugin.
Afaik, Neovim's built-in completion doesn't support it.

[iampi31415]

Hi,

Isn't it this built-in feature?

[mrcjkb]

Signature help is meant primarily to be used by auto completion UIs.

I just tried calling :lua vim.lsp.buf.signature_help() and it appears to depend very much on where your cursor is placed.

Examples:

With the cursor on i of the build() function, I get an INFO message saying "No signature help available":

        Builder::new_multi_thread()
            .enable_all()
            .bu[i]ld()
            .expect("Failed to create a new runtime")

With the cursor on ( of the build() function, I get an INFO message saying "No signature help available":

        Builder::new_multi_thread()
            .enable_all()
            .build[(])
            .expect("Failed to create a new runtime")

With the cursor on the ) of the build function, I get a hover window with some documentation about the build() function:

        Builder::new_multi_thread()
            .enable_all()
            .build([)]
            .expect("Failed to create a new runtime")

With the cursor on x of the expect() function, I get an INFO message saying "No signature help available".

        Builder::new_multi_thread()
            .enable_all()
            .build()
            .e[x]pect("Failed to create a new runtime")

With the cursor anywhere between the parentheses of the expect() function, I get a popup window.