Customize LSP Options With Eglot For Enhanced Bash Formatting

Aug 1, 2025 by ADMIN 62 views

Hey guys! Ever felt the need to tweak your Language Server Protocol (LSP) settings in Emacs, especially when it comes to formatting your code? If you're like me and use Eglot with bash-language-server, you might have run into situations where you want more control over how your code gets formatted. Specifically, when using shfmt through eglot-format-buffer, you might want to leverage its various switches like --case-indent. Let’s dive into how you can achieve this customization.

Understanding the Challenge

First off, let's understand the challenge. The bash-language-server relies on shfmt for formatting, which is fantastic because shfmt is a powerful tool with numerous options to tailor the formatting to your exact preferences. However, Eglot, being a generic LSP client, doesn't directly expose these shfmt options. This means we need a way to tell Eglot how to pass these options to shfmt. This is where the real fun begins, and trust me, it’s totally achievable with a bit of Emacs Lisp magic.

Diving Deep into LSP and Eglot

To truly grasp how to customize LSP options, it's essential to first understand the roles of LSP, Eglot, and the specific language server you're using, in this case, bash-language-server. LSP, or Language Server Protocol, acts as a standardized communication bridge between your editor (Emacs, in our scenario) and language servers. These servers provide features like auto-completion, go-to-definition, and, crucially for us, formatting. Eglot is an Emacs client that speaks the LSP, enabling Emacs to interact with any language server that adheres to the protocol. When you use eglot-format-buffer, you're essentially telling Eglot to ask the language server to format the current buffer. The bash-language-server, in turn, uses shfmt to do the actual formatting. Knowing this flow is crucial because it helps us pinpoint where and how to inject our customizations.

Why Customize `shfmt` Options?

Now, why would you even want to customize shfmt options? Well, shfmt comes packed with a plethora of switches that control various aspects of formatting. For instance, --case-indent dictates how case statements are indented, while others govern brace positioning, error reporting, and more. The default settings might not align with your personal style or your project's coding standards. Customizing these options ensures consistency across your codebase and allows you to enforce a specific style. For example, you might prefer a certain indentation style for case statements or want to ensure that all your scripts adhere to a strict set of formatting rules. By tweaking these options, you're essentially fine-tuning the way your code looks, making it more readable and maintainable.

The Power of Customization

The ability to customize tools like shfmt through Eglot is a testament to the flexibility and power of Emacs and the LSP ecosystem. It allows you to mold your environment to fit your needs, rather than the other way around. This level of control is what makes Emacs such a beloved editor among developers who value customization and efficiency. It’s not just about making your code look pretty; it's about creating a coding environment that works optimally for you, reducing cognitive load and improving your overall workflow. By taking the time to understand and customize these settings, you’re investing in your productivity and the long-term maintainability of your projects.

The Solution: Configuring Eglot to Pass `shfmt` Options

Okay, let's get to the meat of the issue. To pass custom options to shfmt, we need to configure Eglot to include these options when it calls the formatting function. There are a couple of ways to do this, but the most robust and flexible method involves using Eglot's eglot-extend-server-capabilities function. This allows us to modify the server capabilities on a per-language-server basis. This function basically lets you add extra sauce to how Eglot talks to the language server. We’re going to use it to tell Eglot to include our custom shfmt options when formatting Bash code.

Understanding `eglot-extend-server-capabilities`

Before we dive into the code, let's break down what eglot-extend-server-capabilities does. This function is a powerful tool in Eglot's arsenal, designed to let you tweak how Eglot interacts with specific language servers. Think of it as a way to add extra features or modify existing ones on the fly. The function takes two main arguments: the server's name (in our case, bash-language-server) and a list of modifications you want to make. These modifications can include things like adding new commands, changing how certain features are handled, or, as we're going to do, altering the formatting options.

The beauty of eglot-extend-server-capabilities lies in its flexibility. It allows you to target specific language servers, ensuring that your customizations don't interfere with other languages or projects. This is crucial for maintaining a clean and organized Emacs configuration. Moreover, it respects the LSP's capabilities model, meaning you're not just hacking around; you're extending the server's functionality in a way that the LSP anticipates and supports. This approach ensures that your customizations are robust and less likely to break with future updates.

Crafting the Elisp Code

Now, let’s talk code. We need to write some Emacs Lisp to tell Eglot to include our desired shfmt options. This involves defining a function that modifies the formatting capabilities of the bash-language-server. Here's a snippet to get you started:

(defun my-eglot-bash-configure ()
  (eglot-extend-server-capabilities 'bash-language-server
    '((documentFormattingProvider . ((shfmt . ("--case-indent" . "2")))))))

(add-hook 'eglot-managed-mode-hook 'my-eglot-bash-configure)

Let's break this down:

defun my-eglot-bash-configure (): We're defining a function called my-eglot-bash-configure. This function will contain our customization logic.
eglot-extend-server-capabilities 'bash-language-server ...): This is where the magic happens. We're calling eglot-extend-server-capabilities and specifying that we want to modify the capabilities of the bash-language-server.
'((documentFormattingProvider . ((shfmt . ("--case-indent" . "2"))))): This is the core of our customization. We're telling Eglot to modify the documentFormattingProvider capability. Specifically, we're adding a shfmt entry with our desired option, --case-indent, set to 2. This means that shfmt will now indent case statements by two spaces.
(add-hook 'eglot-managed-mode-hook 'my-eglot-bash-configure): Finally, we're adding our function to the eglot-managed-mode-hook. This hook runs whenever Eglot starts managing a buffer, ensuring that our customization is applied whenever we open a Bash file. Think of hooks as triggers that set off a specific action in Emacs. In this case, every time Eglot takes over management of a mode (like Bash mode), our function my-eglot-bash-configure gets executed. This is how we ensure that our custom settings are applied automatically whenever we work on a Bash file.

Diving Deeper into the Elisp Code

Let's further dissect the Elisp code to ensure a crystal-clear understanding. The heart of our customization lies in the nested list structure within the eglot-extend-server-capabilities function. The '((documentFormattingProvider . ((shfmt . ("--case-indent" . "2"))))) part might look a bit intimidating at first, but it's actually quite logical once you break it down.

documentFormattingProvider: This refers to the LSP capability that handles document formatting. We're telling Eglot that we want to modify how this capability is handled for the bash-language-server.
(shfmt . ("--case-indent" . "2")): This is where we specify the shfmt options. We're creating an association list (alist) where the key is shfmt and the value is another alist containing our options. The option --case-indent is set to 2, indicating that we want case statements to be indented by two spaces.

This structure allows us to pass multiple options to shfmt if needed. For example, if you wanted to also set the --indent option to 4, you could extend the alist like this: (shfmt . (("--case-indent" . "2") ("--indent" . "4"))). This flexibility is crucial for tailoring the formatting to your exact preferences.

The add-hook part of the code is equally important. Hooks are a fundamental concept in Emacs Lisp, providing a way to run code at specific points in Emacs' execution. By adding our my-eglot-bash-configure function to the eglot-managed-mode-hook, we ensure that our customizations are applied automatically whenever Eglot starts managing a buffer. This means you don't have to manually run any commands or reload configurations; the settings are applied seamlessly.

Why This Approach?

You might be wondering why we're using this approach with eglot-extend-server-capabilities and hooks, rather than some other method. The key reason is robustness and maintainability. By using Eglot's built-in extension mechanism, we're ensuring that our customizations are compatible with Eglot's internal workings and less likely to break with future updates. Hooks provide a clean and reliable way to trigger our customization logic at the appropriate time, without interfering with other parts of Emacs.

This approach also promotes modularity. By encapsulating our customization logic in a function and attaching it to a hook, we're creating a self-contained unit of code that's easy to understand, modify, and reuse. This is a hallmark of good Emacs Lisp programming and helps keep your configuration organized and manageable.

Applying the Configuration

To apply this configuration, you'll need to add this code to your Emacs configuration file (usually ~/.emacs or ~/.emacs.d/init.el). After adding the code, you'll need to restart Emacs or evaluate the code buffer for the changes to take effect. Once applied, Eglot will automatically pass the --case-indent 2 option to shfmt whenever you format a Bash buffer.

Step-by-Step Guide to Applying the Configuration

Let's walk through the steps to apply this configuration to your Emacs setup. This process is straightforward, but it's essential to follow each step to ensure everything works correctly.

Open your Emacs configuration file: The first step is to open your Emacs configuration file. This is typically located at ~/.emacs or ~/.emacs.d/init.el. You can open it within Emacs by typing C-x C-f (that's Ctrl-x followed by Ctrl-f) and then entering the path to your configuration file.
Add the Elisp code: Once your configuration file is open, paste the Elisp code we discussed earlier into the file. It's a good practice to add a comment above the code to indicate what it does. This helps you (and others) understand the purpose of the code later on. Your configuration file might look something like this:
```
;; Configure Eglot to pass custom shfmt options for Bash formatting
(defun my-eglot-bash-configure ()
  (eglot-extend-server-capabilities 'bash-language-server
    '((documentFormattingProvider . ((shfmt . (("--case-indent" . "2"))))))))

(add-hook 'eglot-managed-mode-hook 'my-eglot-bash-configure)
```
Evaluate the code or restart Emacs: After adding the code, you need to make it active. There are two ways to do this:
- Evaluate the code buffer: This is the quicker method. Place your cursor anywhere within the code you just added and type M-x eval-buffer (that's Alt-x followed by eval-buffer). Emacs will evaluate the code in the buffer, applying the changes immediately.
- Restart Emacs: This is the more thorough method. Close Emacs and reopen it. Emacs will read your configuration file during startup, applying the changes.
Test the configuration: Now that the configuration is applied, it's time to test it. Open a Bash file in Emacs. If Eglot is not already managing the buffer, it should start automatically. You can then try formatting the buffer by typing M-x eglot-format-buffer. If everything is set up correctly, your case statements should now be indented by two spaces.

Troubleshooting Tips

If you encounter any issues, here are a few troubleshooting tips:

Check for syntax errors: Make sure there are no syntax errors in your Elisp code. Emacs Lisp can be picky about syntax, so even a small typo can cause problems. Use the M-x check-parens command to check for mismatched parentheses.
Verify Eglot and bash-language-server are installed: Ensure that both Eglot and bash-language-server are installed and properly configured in your Emacs setup. You can use the M-x package-list-packages command to check if they are installed. If not, install them using M-x package-install.
Check Eglot's logs: Eglot provides logs that can be helpful for diagnosing issues. You can view the logs by typing M-x eglot-events-buffer. Look for any error messages or warnings related to the bash-language-server or formatting.
Experiment with different options: If the --case-indent option isn't working as expected, try experimenting with other shfmt options to see if they are being applied correctly. This can help you isolate the issue.

By following these steps and troubleshooting tips, you should be able to successfully apply the configuration and customize shfmt options through Eglot.

Exploring Further Customizations

But wait, there's more! The beauty of this approach is that it's not limited to just --case-indent. You can pass any shfmt option you want using the same mechanism. Want to change the indentation width? Add ("--indent" . "4"). Want to control brace positioning? Explore the --bn, --bnl, --bps, and --ps options. The possibilities are vast, and you can tailor the formatting precisely to your liking.

Beyond `--case-indent`: A World of `shfmt` Options

The --case-indent option is just the tip of the iceberg when it comes to shfmt customization. shfmt boasts a rich set of options that allow you to control nearly every aspect of Bash code formatting. Let's delve into some of the other options you might find useful and how to incorporate them into your Eglot configuration.

--indent n: This option controls the number of spaces used for indentation. The default is 2, but you can set it to any integer value. For example, --indent 4 will use 4 spaces for indentation.
--bn: This option controls the positioning of braces. When used without any arguments, it keeps the opening brace on the same line as the control statement (e.g., if, for).
--bnl: Similar to --bn, but it forces the opening brace to be on the next line.
--bps: This option puts the opening brace on the same line, but only if there's a space before it.
--ps: This option adds a space between the ) and { in control statements.
--simplify: This option simplifies the code by removing unnecessary semicolons and other syntactic elements.
--version: This option displays the version of shfmt being used.

To incorporate these options into your Eglot configuration, you simply need to add them to the alist in the eglot-extend-server-capabilities function. For example, if you wanted to set the indentation width to 4 spaces and force the opening brace to be on the next line, your code would look like this:

(defun my-eglot-bash-configure ()
  (eglot-extend-server-capabilities 'bash-language-server
    '((documentFormattingProvider . ((shfmt . (("--case-indent" . "2") ("--indent" . "4") ("--bnl" . nil))))))))

(add-hook 'eglot-managed-mode-hook 'my-eglot-bash-configure)

Notice how we've added ("--indent" . "4") and ("--bnl" . nil) to the alist. The value nil for --bnl indicates that we want to enable this option. You can add as many options as you need, allowing you to fine-tune the formatting to your exact specifications.

Experimentation is Key

The best way to discover the perfect formatting style for your Bash code is to experiment with different shfmt options. Try changing the indentation width, brace positioning, and other settings to see how they affect the look and feel of your code. Don't be afraid to try different combinations of options to find what works best for you.

Remember, consistency is key when it comes to code formatting. Once you've settled on a set of options, stick with them across your projects to ensure a uniform style. This will make your code more readable and maintainable in the long run.

Sharing Your Configurations

Customizing your code formatting is a personal endeavor, but it can also be a collaborative one. If you're working on a team, it's a good idea to share your shfmt configurations to ensure everyone is using the same style. You can do this by sharing your Emacs configuration file or by creating a dedicated configuration file for shfmt and including it in your project.

By sharing your configurations, you can foster a consistent coding style across your team, making it easier to collaborate and maintain your codebase. This is especially important for large projects with multiple contributors.

Conclusion

So there you have it! Customizing LSP options with Eglot is not only possible but also quite powerful. By leveraging eglot-extend-server-capabilities and understanding how Eglot interacts with language servers, you can tailor your development environment to your exact needs. This approach ensures that your Bash code is formatted exactly how you like it, making your code more readable and maintainable. Happy coding, and may your Bash scripts always be beautifully formatted!

The Power of Customization and the Emacs Ecosystem

Customizing LSP options with Eglot is a prime example of the power and flexibility of the Emacs ecosystem. Emacs is renowned for its extensibility, allowing users to tailor the editor to their specific workflows and preferences. This level of customization is a key reason why Emacs remains a favorite among developers who value control and efficiency.

By providing tools like eglot-extend-server-capabilities, Eglot embraces this Emacs philosophy, allowing you to seamlessly integrate your own customizations into the LSP workflow. This ensures that you're not just using a generic editor; you're crafting a personalized development environment that perfectly suits your needs.

This approach also highlights the importance of understanding the underlying technologies you're using. By understanding how LSP, Eglot, and shfmt work together, you can effectively troubleshoot issues and implement complex customizations. This knowledge empowers you to take full control of your development environment and become a more proficient developer.

In conclusion, customizing LSP options with Eglot is a rewarding endeavor that can significantly enhance your coding experience. It's a testament to the power of open-source tools and the flexibility of the Emacs ecosystem. So, dive in, experiment with different options, and create a development environment that truly reflects your style and preferences. Your beautifully formatted Bash scripts will thank you for it!