Add minimal param LSP server example by MarcSkovMadsen · Pull Request #109 · MarcSkovMadsen/holoviz-mcp

MarcSkovMadsen · 2026-01-18T04:30:16Z

Just vibe code a param LSP server to better understand what is possible and what it could help with.

The extension installed

Hover over class attribute provides parameter details

Hover over instance attribute provides parameter details

Copilot

Pull request overview

This PR adds a proof-of-concept Language Server Protocol (LSP) implementation for param.Parameterized classes, providing IDE features like hover documentation, autocompletion, and diagnostics for param parameters in VS Code.

Changes:

Implements a minimal LSP server in Python using pygls that provides hover, completion, and diagnostic features for param types
Creates a VS Code extension client to connect to the LSP server
Adds comprehensive tests and example files demonstrating the functionality

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
examples/param-lsp/param_lsp.py	Core LSP server implementation with hover, completion, and diagnostic features
examples/param-lsp/test_param_lsp.py	Unit tests for LSP server functions
examples/param-lsp/example_parameterized.py	Example parameterized classes for testing LSP features
examples/param-lsp/README.md	Comprehensive documentation covering installation, usage, and limitations
examples/param-lsp/vscode-client/package.json	VS Code extension manifest
examples/param-lsp/vscode-client/extension.js	VS Code extension entry point that launches the LSP server
.pre-commit-config.yaml	Restricts eslint to holoviz_mcp directory
.gitignore	Adds ignore patterns for node_modules and extension build artifacts

Copilot · 2026-01-18T04:33:46Z

+def parse_param_args(args_str: str) -> dict:
+    """Parse parameter arguments from the declaration string."""
+    result = {}
+    # Simple parsing for common kwargs
+    for match in re.finditer(r"(\w+)\s*=\s*([^,]+?)(?:,|$)", args_str):
+        key, value = match.groups()
+        result[key.strip()] = value.strip()
+    # Check for positional default (first arg without =)
+    first_arg = args_str.split(",")[0].strip() if args_str else ""
+    if first_arg and "=" not in first_arg:
+        result["default"] = first_arg
+    return result


The parse_param_args function uses a simple regex that doesn't handle nested parentheses, tuples, or complex values correctly. For example, bounds=(0, 100) will be parsed as bounds='(0' (as acknowledged in test line 38). Consider using a more robust parser like ast.literal_eval or a proper tokenizer to handle nested structures.

Copilot · 2026-01-18T04:33:46Z

+    # Check if cursor is within the match
+    start = match.start()
+    end = match.end()
+    if not (start <= position.character <= end):


The condition check only verifies if the cursor position is within the match, but the match object already confirms the line matches. The character position check should ensure the cursor is specifically on the parameter name or type, not just anywhere in the declaration. Consider refining this to provide more accurate hover positions.

Suggested change

# Check if cursor is within the match

start = match.start()

end = match.end()

if not (start <= position.character <= end):

# Only trigger when cursor is on the parameter name or type, not anywhere in the declaration

name_start, name_end = match.span(1)

type_start, type_end = match.span(2)

if not (

name_start <= position.character <= name_end

or type_start <= position.character <= type_end

):

Copilot · 2026-01-18T04:33:47Z

+def find_instance_class(document: TextDocument, var_name: str) -> str | None:
+    """Find the class name for a variable assignment like 'person = Person(...)'."""
+    for line in document.source.split("\n"):
+        match = INSTANCE_PATTERN.match(line)
+        if match and match.group(1) == var_name:
+            return match.group(2)
+    return None


The function find_instance_class only looks for direct assignments in the current file and doesn't handle imports or assignments in other scopes. This means hovering over instance attributes will fail if the instance was created in a different file or imported. Consider documenting this limitation clearly or tracking variable scope more accurately.

Copilot · 2026-01-18T04:33:47Z

+    assert result["bounds"] == "(0"  # Simple parsing doesn't handle nested parens well
+    assert result["doc"] == "'A number'"


The test acknowledges that the parser doesn't handle nested parentheses correctly by checking for the incorrect value '(0' instead of '(0, 100)'. This test is validating broken behavior rather than correct behavior. Either fix the parser to handle nested structures correctly or document this as a known limitation with a TODO comment.

Copilot · 2026-01-18T04:33:47Z

+        skills=["Python", "Data Science"],
+    )
+
+    print(f"Person: {person.name}, {person.age} years old", person.email)


Missing comma after print statement arguments. This will cause a syntax error. Should be print(f"Person: {person.name}, {person.age} years old", person.email) → print(f"Person: {person.name}, {person.age} years old, {person.email}")

Copilot · 2026-01-18T04:33:48Z

+}
+
+# Regex to find param declarations: name = param.Type(...)
+PARAM_PATTERN = re.compile(r"^\s*(\w+)\s*=\s*(param\.(\w+))\s*\(([^)]*)\)", re.MULTILINE)


The regex pattern PARAM_PATTERN only matches single-line parameter declarations. Multi-line declarations like name = param.String(\n default="value"\n) will not be detected. Consider using the re.DOTALL flag or implementing a more robust parsing strategy.

Copilot · 2026-01-18T04:33:48Z

@@ -58,6 +58,7 @@ repos:
    rev: v9.13.0
    hooks:


The added files pattern restricts eslint to only check files in holoviz_mcp/ directory, which means the JavaScript files in examples/param-lsp/vscode-client/ won't be linted. This is inconsistent with having JavaScript code in the repository. Consider either extending the pattern to include example JS files or documenting why they're excluded.

Suggested change

hooks:

hooks:

# NOTE: This eslint hook is intentionally limited to the holoviz_mcp package.

# Example JavaScript/TypeScript files under examples/ (e.g.

# examples/param-lsp/vscode-client/) are not linted by this hook.

Copilot · 2026-01-18T04:33:48Z

+                    message=f"{type_name} should specify 'objects' parameter",
+                    severity=lsp.DiagnosticSeverity.Warning,


The diagnostic for Selector types checks if 'objects' is missing, but according to param documentation and the example_parameterized.py file, Selector can have 'objects' as a keyword argument. However, a Selector can also accept a default value and infer objects from that. The diagnostic might produce false positives. Consider refining this check or downgrading the severity.

Suggested change

message=f"{type_name} should specify 'objects' parameter",

severity=lsp.DiagnosticSeverity.Warning,

message=(

f"Consider specifying 'objects' for {type_name}, or ensure the "

"default value clearly defines the available options"

),

severity=lsp.DiagnosticSeverity.Hint,

Copilot · 2026-01-18T04:33:48Z

+    // Path to the Python LSP server - use absolute path
+    const serverPath = '/home/jovyan/repos/private/holoviz-mcp/examples/param-lsp/param_lsp.py';


This hardcoded absolute path will break for any other user. Consider using a relative path from the extension directory or making it configurable through VS Code settings. You could use path.join(__dirname, '..', 'param_lsp.py') to construct a relative path.

Suggested change

// Path to the Python LSP server - use absolute path

const serverPath = '/home/jovyan/repos/private/holoviz-mcp/examples/param-lsp/param_lsp.py';

// Path to the Python LSP server - resolve relative to this extension directory

const serverPath = path.join(__dirname, '..', 'param_lsp.py');

Copilot · 2026-01-18T04:33:49Z

@@ -0,0 +1,46 @@
+const path = require('path');


Unused variable path.

Suggested change

const path = require('path');

Add minimal param LSP server example

6b436d6

Copilot AI review requested due to automatic review settings January 18, 2026 04:30

Copilot started reviewing on behalf of MarcSkovMadsen January 18, 2026 04:30 View session

Copilot AI reviewed Jan 18, 2026

View reviewed changes

MarcSkovMadsen closed this Jan 18, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Add minimal param LSP server example#109

Add minimal param LSP server example#109
MarcSkovMadsen wants to merge 1 commit into
mainfrom
enhancement/lsp

MarcSkovMadsen commented Jan 18, 2026 •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Copilot AI Jan 18, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

		assert result["bounds"] == "(0" # Simple parsing doesn't handle nested parens well
		assert result["doc"] == "'A number'"

-    hooks:
+    hooks:
+      # NOTE: This eslint hook is intentionally limited to the holoviz_mcp package.
+      # Example JavaScript/TypeScript files under examples/ (e.g.
+      # examples/param-lsp/vscode-client/) are not linted by this hook.

		message=f"{type_name} should specify 'objects' parameter",
		severity=lsp.DiagnosticSeverity.Warning,

-                    message=f"{type_name} should specify 'objects' parameter",
-                    severity=lsp.DiagnosticSeverity.Warning,
+                    message=(
+                        f"Consider specifying 'objects' for {type_name}, or ensure the "
+                        "default value clearly defines the available options"
+                    ),
+                    severity=lsp.DiagnosticSeverity.Hint,

		// Path to the Python LSP server - use absolute path
		const serverPath = '/home/jovyan/repos/private/holoviz-mcp/examples/param-lsp/param_lsp.py';

Conversation

MarcSkovMadsen commented Jan 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 18, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

MarcSkovMadsen commented Jan 18, 2026 •

edited

Loading