npm: Use fs API to read package.json, avoid LSP notification spam

[Copilot]

The npm extension was opening every package.json as a text document during task discovery, triggering textDocument/didOpen|didClose to all LSP servers with JSON documentSelector. Large projects with 100+ package.json files would generate 200+ notifications.

Changes

• Replace workspace.openTextDocument() with workspace.fs.readFile() in getScripts()

  • Reads file content without entering text document manager
  • Uses TextDecoder for cross-platform portability
  • Creates IPositionOffsetTransformer interface for position/offset transformation
  • Implements PositionOffsetTransformer class that provides only the minimal required functionality (uri, positionAt())

• Add LRU cache with workspace storage persistence for parsed package.json scripts

  • 128 entry limit with least-recently-used eviction
  • Loads cache from workspace storage on activation
  • Persists cache changes to workspace storage asynchronously
  • Skip re-reading unchanged files using mtime validation
  • Clear cache in invalidateTasksCache()

Implementation

// Before: triggered LSP notifications
const document = await workspace.openTextDocument(packageJsonUri);
return readScripts(document);

// After: direct file read with LRU caching and proper interface
const stat = await workspace.fs.stat(packageJsonUri);
const cached = packageJsonCache.get(packageJson);
if (cached && cached.mtime === stat.mtime) {
    return cached.scripts;
}
const content = await workspace.fs.readFile(packageJsonUri);
const text = new TextDecoder('utf-8').decode(content);
const transformer = new PositionOffsetTransformer(packageJsonUri, text);
const scripts = readScripts(transformer, text);
packageJsonCache.set(packageJson, { mtime: stat.mtime, scripts });

The IPositionOffsetTransformer interface defines the minimal contract needed for position/offset conversion. The PositionOffsetTransformer class implements this interface, handling both Unix and Windows line endings, using binary search for positionAt() performance. The readScripts() function is refactored to accept IPositionOffsetTransformer instead of TextDocument, maintaining backward compatibility since TextDocument already implements the required interface.

The PackageJsonLRUCache class implements an LRU eviction policy with workspace storage persistence, ensuring the cache survives VS Code restarts while preventing unbounded memory growth in large projects.

File content decoding uses the standard TextDecoder API for better portability across Node.js and browser environments.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>documentSelector json for LSP-Connection will spam textDocument/didOpen|didClose request for all package.json</issue_title>
<issue_description>
Type: Bug

coming from: oxc-project/oxc#17615 (comment)
Possible duplicate, but the server is just waiting for textDocument/formatting: #238935

my extension want to use the following code:

// This list is not used as-is for implementation to determine whether formatting processing is possible.
    const supportedExtensions = [
      "json"
       // ... other extension
    ];

    const clientOptions: LanguageClientOptions = {
      // Register the server for plain text documents
      documentSelector: [
        {
          pattern: `**/*.{${supportedExtensions.join(",")}}`,
          scheme: "file",
        },
      ],
      ...
  }

I tried with a new documentSelector on clientOptions. With {language: "json"} too, same bug.

When the server is started, VS Code will send, for every package.json in the project, a textDocument/didOpen and textDocument/didClose notification to the server. Even if you have only a TypeScript file open.
With a big project, this can send over 100 requests to the server.
Without json, the server is just waiting, after dynamic registrations, for the formatting request.

Try it yourself with the oxc git pull request and these settings.

{
  "oxc.trace.server": "verbose",
  "oxc.path.oxfmt": "apps/oxfmt/dist/cli.js", // debug with local oxfmt build
  "oxc.fmt.configPath": "oxfmtrc.jsonc",
  "editor.defaultFormatter": "oxc.oxc-vscode",
  "editor.formatOnSave": true
}

You need to rebase, execute these commands and restart the editor after it:

cd editors/vscode
pnpm install
pnpm oxfmt:build:debug
pnpm compile
pnpm package
pnpm install-extension

These are my export from the output channel: Oxc (Fmt).log, after some minutes these will happend again (without doing something): Oxc (Fmt)2.log

VS Code version: Code 1.107.1 (994fd12, 2025-12-17T14:15:14.850Z)
OS version: Windows_NT x64 10.0.26200
Modes:
Remote OS version: Linux x64 6.6.87.2-microsoft-standard-WSL2

System Info

Item	Value
CPUs	AMD Ryzen 9 7900X 12-Core Processor (24 x 4700)
GPU Status	2d_canvas: enabled direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off trees_in_viz: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	undefined
Memory (System)	31.10GB (5.32GB free)
Process Argv	--folder-uri=vscode-remote://wsl+Ubuntu/home/sysix/dev/oxc --remote=wsl+Ubuntu --crash-reporter-id 2b3612a4-60c2-4760-b864-459fece876bf
Screen Reader	no
VM	0%

Item	Value
Remote	WSL: Ubuntu
OS	Linux x64 6.6.87.2-microsoft-standard-WSL2
CPUs	AMD Ryzen 9 7900X 12-Core Processor (24 x 0)
Memory (System)	15.17GB (8.94GB free)
VM	0%

Extensions (39)

Extension	Author (truncated)	Version
vscode-jetbrains-keybindings	isu	0.1.9
remote-containers	ms-	0.434.0
remote-wsl	ms-	0.104.3
vscode-icons	vsc	12.15.0
rust-bundle	1Yi	1.0.0
vscode-intelephense-client	bme	1.16.3
vscode-eslint	dba	3.0.20
composer-php-vscode	DEV	1.64.18270
intelli-php-vscode	DEV	0.12.17700
phptools-vscode	DEV	1.64.18270
profiler-php-vscode	DEV	1.64.18270
docker	doc	0.18.0
githistory	don	0.6.20
EditorConfig	Edi	0.17.4
prettier-vscode	esb	11.0.2
dependi	fil	0.7.21
copilot-chat	Git	0.35.3
vscode-github-actions	git	0.29.1
gti-vscode	Gra	0.6.1
php-cs-fixer	jun	0.3.21
git-graph	mhu	1.30.0
vscode-containers	ms-	2.3.0
vscode-docker	ms-	2.0.0
extension-test-runner	ms-	0.0.14
live-server	ms-	0.4.16
vscode-just-syntax	nef	0.8.0
indent-rainbow	ode	8.3.1
oxc-vscode	oxc	1.38.0
vscode-yaml	red	1.19.1
rust-analyzer	rus	0.3.2743
vscode-coverage-gutters	rya	2.14.0
markdown-preview-enhanced	shd	0.8.20
code-spell-checker	str	4.4.0
even-better-toml	tam	0.21.2
typos-vscode	tek	0.1.47
vscode-lldb	vad	1.11.4
volar	Vue	3.2.2
gitblame	wad	11.2.0
markdown-all-in-one	yzh	3.6.3

A/B Experiments

vsliv368:30146709
pythonvspyt551:31249599
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31436602
aj953862:31281341
6abeh943:31336334
cloudbuttont:31379625
3efgi100_wstrepl:31403338
use-responses-a...

</details>



<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes microsoft/vscode#286455

<!-- START COPILOT CODING AGENT TIPS -->
---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more [Copilot coding agent tips](https://gh.io/copilot-coding-agent-tips) in the docs.

[connor4312]

Don't try to fake a text document. Instead, make readScripts's first document be an IPositionOffsetTransformer, which matches the minimal types of the document but otherwise has an implementation that can be used for strings.

[Copilot]

Done in commit 849be58. Created IPositionOffsetTransformer interface and refactored readScripts to accept it instead of TextDocument. The PositionOffsetTransformer class now properly implements this interface without faking VS Code APIs.

[connor4312]

Getting there. Now a few more things:

1. Use an LRU cache for package.json entries (set to 128 items)
2. Persist the LRU cache in the workspace storage on the vscode.ExtensionContext (passed to the activate() method)

[Copilot]

Done in commit 2a2cf9a. Implemented PackageJsonLRUCache class with:

1. 128 entry limit with LRU eviction
2. Loads from workspace storage on initialization
3. Persists to workspace storage asynchronously on changes
4. Initialized in activate() with the ExtensionContext

[connor4312]

Use TextDecoder here for portability @copilot

[Copilot]

Done in commit fc51b35. Replaced Buffer.from(content).toString('utf8') with new TextDecoder('utf-8').decode(content) for better portability.