Kotlinx Coroutines Insight for VS Code

A Visual Studio Code extension that brings JetBrains-style coroutine insight to any Kotlin file: every suspension point is highlighted in the gutter, and extra navigation / hover affordances make it trivial to reason about where your coroutine actually suspends.

Features


Gutter icon at every suspension point	Uses the official JetBrains `suspendCall` glyph (light + dark variants).
Inlay hint (`suspend` / `await`) at call sites	Eyes-on-keyboard reminder that this call yields the dispatcher.
CodeLens above every `suspend fun`	Shows the number of suspension points contained inside.
Hover on builders, suspend calls, `.await()` and Flow terminals	Cheat-sheet documentation for `runBlocking`, `withContext`, `withTimeoutOrNull`, …
Status-bar counter on Kotlin files	Click to jump to the next suspension point.
Navigation commands	`Alt+↓` / `Alt+↑` cycle through suspension points; great for code reviews.
Pure regex tokenizer, zero LSP required	A 2 000-line file is analyzed in well under a millisecond. Updates run debounced on every keystroke.

Detected constructs

suspend fun foo(...) declarations
Coroutine builders: runBlocking, launch, async, withContext, coroutineScope, supervisorScope, withTimeout(OrNull), flow, channelFlow, callbackFlow, produce, actor, runTest
Stdlib suspend calls: delay, yield, awaitAll, awaitCancellation, join, joinAll, select, suspendCancellableCoroutine, …
.await() on Deferred / Job
Flow terminal operators: collect, collectLatest, first(OrNull), last(OrNull), single(OrNull), toList, toSet, count, fold, reduce, launchIn, stateIn, shareIn
Calls to other suspend funs declared earlier in the same file

You can extend the dictionary via:

// .vscode/settings.json
{
  "kotlinxCoroutines.extraSuspendFunctions": ["myInternalAwait", "fetchPage"],
  "kotlinxCoroutines.extraCoroutineBuilders": ["myScope.background"]
}

Configuration

Setting	Default	Description
`kotlinxCoroutines.gutterIcons.enabled`	`true`	Show the suspendCall arrow in the gutter.
`kotlinxCoroutines.inlayHints.enabled`	`true`	Show inline `suspend` / `await` hints.
`kotlinxCoroutines.codeLens.enabled`	`true`	Show "N suspension points" CodeLens above suspend funs.
`kotlinxCoroutines.statusBar.enabled`	`true`	Show a status-bar counter on Kotlin files.
`kotlinxCoroutines.extraSuspendFunctions`	`[]`	Extra bare names to treat as suspend calls.
`kotlinxCoroutines.extraCoroutineBuilders`	`[]`	Extra bare names to treat as coroutine builders.

Sample project

The repository ships with a ready-to-debug Gradle sample under sample/. Press F5 in this repo to launch a new Extension Development Host pre-opened on the sample workspace and watch the suspendCall arrows light up across Main.kt, FlowDemo.kt and the unit test.

sample/
├── settings.gradle.kts        # includes :app and :flowDemo
├── build.gradle.kts
├── app/
│   ├── build.gradle.kts
│   └── src/{main,test}/kotlin/sample/app/
└── flowDemo/
    ├── build.gradle.kts
    └── src/main/kotlin/sample/flowdemo/

Building the extension

bun install                  # or: npm install
bun run compile              # or: npm run compile
bun run test                 # vitest unit tests
node scripts/generate_icon.js   # (re)generate images/icon.png

Then either press F5 or package with vsce package.

How it works

The extension does not rely on a Kotlin language server. Instead it ships a minimal Kotlin tokenizer that:

Strips comments and string literals (preserving newlines for accurate line numbers).
Locates every suspend fun and computes the byte range of its body via brace matching.
Walks identifiers, classifying calls as coroutine builder / suspend call / .await() / Flow terminal based on a curated dictionary plus the user-supplied extension lists.
Tracks coroutine-builder lambda bodies as additional "suspend contexts" so that hover messages can warn when a suspending call appears outside any coroutine.

This pure-text approach makes per-keystroke updates trivially cheap while covering the 95 % of real-world coroutine code. Pull requests adding more detectors are very welcome.

License

MIT.

Kotlinx Coroutines Insight

r0kuko