Add WASM support: --wasm flag with Node.js and Deno runtimes by lostflydev · Pull Request #1 · lostflydev/scala-cli

lostflydev · 2026-03-06T09:50:14Z

Implements scala-cli issue VirtusLab#3316: integrate WebAssembly with Scala CLI.

What's added

--wasm CLI flag and //> using wasm directive to enable WASM output
--wasm-runtime <runtime> option and //> using wasmRuntime directive Supported values: node (default), deno, wasmtime, wasmedge, wasmer
--deno-version, --wasmtime-version, --wasmer-version options and corresponding directives for pinning runtime versions

Runtime support

Node.js (default): runs Scala.js WASM output with --experimental-wasm-exnref flag, requires Node.js >= 22
Deno: runs Scala.js WASM output; if not found on PATH, downloads automatically from GitHub releases via Coursier cache
Wasmtime / WasmEdge / Wasmer: return UnsupportedWasmRuntimeError pending upstream Scala.js standalone WASM support (Make Scala.js Wasm backend suitable for standalone Wasm VMs (a.k.a. support "server-side Wasm") scala-js/scala-js#4991)

…VirtusLab#4173) Bumps the npm-dependencies group in /website with 1 update: [@algolia/client-search](https://github.com/algolia/algoliasearch-client-javascript). Updates `@algolia/client-search` from 5.49.1 to 5.49.2 - [Release notes](https://github.com/algolia/algoliasearch-client-javascript/releases) - [Changelog](https://github.com/algolia/algoliasearch-client-javascript/blob/main/CHANGELOG.md) - [Commits](algolia/algoliasearch-client-javascript@5.49.1...5.49.2) --- updated-dependencies: - dependency-name: "@algolia/client-search" dependency-version: 5.49.2 dependency-type: direct:production update-type: version-update:semver-patch dependency-group: npm-dependencies ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Bumps the github-actions group with 4 updates: [docker/login-action](https://github.com/docker/login-action), [docker/metadata-action](https://github.com/docker/metadata-action), [docker/setup-buildx-action](https://github.com/docker/setup-buildx-action) and [docker/build-push-action](https://github.com/docker/build-push-action). Updates `docker/login-action` from 3 to 4 - [Release notes](https://github.com/docker/login-action/releases) - [Commits](docker/login-action@v3...v4) Updates `docker/metadata-action` from 5 to 6 - [Release notes](https://github.com/docker/metadata-action/releases) - [Commits](docker/metadata-action@v5...v6) Updates `docker/setup-buildx-action` from 3 to 4 - [Release notes](https://github.com/docker/setup-buildx-action/releases) - [Commits](docker/setup-buildx-action@v3...v4) Updates `docker/build-push-action` from 6 to 7 - [Release notes](https://github.com/docker/build-push-action/releases) - [Commits](docker/build-push-action@v6...v7) --- updated-dependencies: - dependency-name: docker/login-action dependency-version: '4' dependency-type: direct:production update-type: version-update:semver-major dependency-group: github-actions - dependency-name: docker/metadata-action dependency-version: '6' dependency-type: direct:production update-type: version-update:semver-major dependency-group: github-actions - dependency-name: docker/setup-buildx-action dependency-version: '4' dependency-type: direct:production update-type: version-update:semver-major dependency-group: github-actions - dependency-name: docker/build-push-action dependency-version: '7' dependency-type: direct:production update-type: version-update:semver-major dependency-group: github-actions ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

…ributions

Add LLM policy & a PR template

Bumps [undici](https://github.com/nodejs/undici) from 7.18.2 to 7.24.1. - [Release notes](https://github.com/nodejs/undici/releases) - [Commits](nodejs/undici@v7.18.2...v7.24.1) --- updated-dependencies: - dependency-name: undici dependency-version: 7.24.1 dependency-type: indirect ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

…b#4180)

Bumps the github-actions group with 1 update: [webfactory/ssh-agent](https://github.com/webfactory/ssh-agent). Updates `webfactory/ssh-agent` from 0.9.1 to 0.10.0 - [Release notes](https://github.com/webfactory/ssh-agent/releases) - [Changelog](https://github.com/webfactory/ssh-agent/blob/master/CHANGELOG.md) - [Commits](webfactory/ssh-agent@a6f90b1...e838748) --- updated-dependencies: - dependency-name: webfactory/ssh-agent dependency-version: 0.10.0 dependency-type: direct:production update-type: version-update:semver-minor dependency-group: github-actions ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

…ile by lines to improve framework discovery (VirtusLab#4185)

Bumps the npm-dependencies group in /website with 1 update: [sass](https://github.com/sass/dart-sass). Updates `sass` from 1.97.3 to 1.98.0 - [Release notes](https://github.com/sass/dart-sass/releases) - [Changelog](https://github.com/sass/dart-sass/blob/main/CHANGELOG.md) - [Commits](sass/dart-sass@1.97.3...1.98.0) --- updated-dependencies: - dependency-name: sass dependency-version: 1.98.0 dependency-type: direct:production update-type: version-update:semver-minor dependency-group: npm-dependencies ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

…with disabled build server (VirtusLab#4181)

…tusLab#4178)

Co-authored-by: gh-actions <actions@github.com>

* Bump `jsoup` to 1.22.2 (was 1.22.1) * Bump `jsoniter-scala` to 2.38.14 (was 2.38.8) * Bump `scalaMeta` to 4.17.0 (was 4.15.2) * Bump `asm` to 9.10.1 (was 9.9.1) * Bump `javaSemanticdb` to 0.12.3 (was 0.10.0) * Bump `scalafix` to 0.14.6 (was 0.14.5) * Bump `guava` to 33.6.0-jre (was 33.5.0-jre) * Bump `jgit` to 7.6.0.202603022253-r (was 7.5.0.202512021534-r) * Bump `scalaPackager` to 0.2.2 (was 0.2.1) * Bump `metaconfig-typesafe-config` to 0.18.6 (was 0.18.2) * Bump `scalajs-env-nodejs` to 1.6.0 (was 1.5.0) * Bump `pprint` to 0.9.6 (was 0.9.5) * Bump `sbt` to 1.12.5 (was 1.12.4) * Bump `mavenScalaCompilerPlugin` to 4.9.10 (was 4.9.1) * Bump `munit` to 1.3.0 (was 1.2.2)

…#4300) Bumps the npm-dependencies group in /website with 5 updates: | Package | From | To | | --- | --- | --- | | [@algolia/client-search](https://github.com/algolia/algoliasearch-client-javascript) | `5.52.1` | `5.53.0` | | [@easyops-cn/docusaurus-search-local](https://github.com/easyops-cn/docusaurus-search-local/tree/HEAD/packages/docusaurus-search-local) | `0.55.1` | `0.55.2` | | [react](https://github.com/facebook/react/tree/HEAD/packages/react) | `19.2.6` | `19.2.7` | | [@types/react](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/react) | `19.2.15` | `19.2.16` | | [react-dom](https://github.com/facebook/react/tree/HEAD/packages/react-dom) | `19.2.6` | `19.2.7` | Updates `@algolia/client-search` from 5.52.1 to 5.53.0 - [Release notes](https://github.com/algolia/algoliasearch-client-javascript/releases) - [Changelog](https://github.com/algolia/algoliasearch-client-javascript/blob/main/CHANGELOG.md) - [Commits](algolia/algoliasearch-client-javascript@5.52.1...5.53.0) Updates `@easyops-cn/docusaurus-search-local` from 0.55.1 to 0.55.2 - [Release notes](https://github.com/easyops-cn/docusaurus-search-local/releases) - [Commits](https://github.com/easyops-cn/docusaurus-search-local/commits/v0.55.2/packages/docusaurus-search-local) Updates `react` from 19.2.6 to 19.2.7 - [Release notes](https://github.com/facebook/react/releases) - [Changelog](https://github.com/facebook/react/blob/main/CHANGELOG.md) - [Commits](https://github.com/facebook/react/commits/v19.2.7/packages/react) Updates `@types/react` from 19.2.15 to 19.2.16 - [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases) - [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/react) Updates `react-dom` from 19.2.6 to 19.2.7 - [Release notes](https://github.com/facebook/react/releases) - [Changelog](https://github.com/facebook/react/blob/main/CHANGELOG.md) - [Commits](https://github.com/facebook/react/commits/v19.2.7/packages/react-dom) --- updated-dependencies: - dependency-name: "@algolia/client-search" dependency-version: 5.53.0 dependency-type: direct:production update-type: version-update:semver-minor dependency-group: npm-dependencies - dependency-name: "@easyops-cn/docusaurus-search-local" dependency-version: 0.55.2 dependency-type: direct:production update-type: version-update:semver-patch dependency-group: npm-dependencies - dependency-name: react dependency-version: 19.2.7 dependency-type: direct:production update-type: version-update:semver-patch dependency-group: npm-dependencies - dependency-name: "@types/react" dependency-version: 19.2.16 dependency-type: direct:production update-type: version-update:semver-patch dependency-group: npm-dependencies - dependency-name: react-dom dependency-version: 19.2.7 dependency-type: direct:production update-type: version-update:semver-patch dependency-group: npm-dependencies ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Implements scala-cli issue VirtusLab#3316: integrate WebAssembly with Scala CLI. - `--wasm` CLI flag and `//> using wasm` directive to enable WASM output - `--wasm-runtime <runtime>` option and `//> using wasmRuntime` directive Supported values: node (default), deno - `--deno-version`, `--wasmtime-version`, `--wasmer-version` options and corresponding directives for pinning runtime versions - **Node.js** (default): runs Scala.js WASM output with `--experimental-wasm-exnref` flag, requires Node.js >= 22 - **Deno**: runs Scala.js WASM output

…imes - Move --wasm flag to dedicated Wasm help group with --help-wasm option - Simplify wasmOptions parsing with fold/toRight pattern - Add runtime validation with UnrecognizedWasmRuntimeError in directives - Auto-enable WASM when wasmRuntime directive is set - Update reference documentation Code style: simplify denoNeedsWasmFlag, explicit runtime match cases, clean type annotation, scalfmt

…smRuntime bun) - Add BunNotFoundError with install hint - Add integration test for Bun (conditional on bun being on PATH) - Add actions/setup-node@v6 node-version:24 to all Linux integration test jobs: the default Node.js on ubuntu-24.04 runners is too old for Scala.js WASM GC (which requires Node.js >= 22). Matches docs-tests job which already pins node-version: 24

@main

Node 24 still ships V8 12.x where wasm-exnref is gated behind --experimental-wasm-exnref; the flag only flips to default in V8 13.x (Node 25+). The previous nodeMajorVersion < 24 guard therefore left Node 24 (the version pinned in CI) without the flag, which made any Scala.js WASM code using exception bytecodes, runtime throws, JS interop or Scala 3 @main fail at runtime. Same reasoning applies to Deno (Deno 2.x = V8 12.x). Until V8 13.x is the default everywhere, just always set the flag, there is no any overhead

…efactor into ScalaJsOptions - Replace "WASM" with "Wasm" per WebAssembly spec: contraction, not acronym - Fix nodeNeedsWasmFlag to be version-aware: only pass --experimental-wasm-exnref for Node < 25 (V8 12.x); Node 25+ has it enabled by default, Node 26+ may remove it - Remove Node/Bun pre-flight version checks; let runtime fail naturally on old versions - Remove else-if-emitWasm branch (not needed) - Refactor WasmOptions into ScalaJsOptions: jsEmitWasm and wasmRuntime are now fields of ScalaJsOptions at both build and CLI layers; CLI flags are now --js-emit-wasm and --js-wasm-runtime under the Wasm help group; WasmOptions classes removed - linkerConfig() now forces ESModule when jsEmitWasm=true - Update all integration test CLI flags to --js-emit-wasm / --js-wasm-runtime

- Log when --experimental-wasm-exnref is injected in runJs (Node.js < 25) - Log when Wasm mode enables ES module output in Run.scala - Improve comment in Wasm.scala directive to reference AmbiguousPlatformError for --wasm + --platform native conflict detection

- runDeno: append --experimental-wasm-exnref to existing DENO_V8_FLAGS instead of silently replacing user-defined flags; log when flag is set - ScalaJsOptions.linkerConfig: warn when Wasm overrides user-specified --js-module-kind (forced to ESModule by Wasm backend)

Lost during Run.scala restructure for Wasm: restores the original case _: SbtFile => "" and case null => "" branches so SbtFile inputs are properly filtered from scala.sources JVM property.

…e to --js-runtime - Remove the exnref capability probe and all --experimental-wasm-exnref / DENO_V8_FLAGS injection (tanishiking). scala-cli no longer manages V8 flags; on older runtimes that still gate exnref, users pass it via NODE_OPTIONS / DENO_V8_FLAGS. CI runtimes (node 24, deno 2.x, bun) need none. - Stop forcing ESModule for Wasm; fail fast with WasmModuleKindError when --js-module-kind isn't es, instead of silently overriding it. Keeps config consistent with Scala.js and future module kinds. - Rename --js-wasm-runtime -> --js-runtime and //> using wasmRuntime -> //> using jsRuntime; selecting a runtime no longer auto-enables Wasm. - Update integration tests (explicit --js-module-kind es, renamed flag, fail-fast test) and the Wasm guide; regenerate reference docs.

lostflydev force-pushed the scala-wasm-support branch 5 times, most recently from c6453eb to ddfadbc Compare March 9, 2026 05:51

Gedochao and others added 3 commits March 9, 2026 13:33

Bump Mill to 1.1.3 (was 1.1.2) (VirtusLab#4169)

90aa8d7

lostflydev force-pushed the scala-wasm-support branch from ddfadbc to cf1e65a Compare March 10, 2026 15:04

Gedochao and others added 16 commits March 12, 2026 11:42

Update Scala 3 Next RC to 3.8.3-RC2 (VirtusLab#4175)

4763be0

Refer the Scala 3 compiler policy on usage of LLM-based tools in cont…

1631f8c

…ributions

Add a PR template

03ec06a

Support --cross with the package sub-command (VirtusLab#4171)

48fa471

Allow to --watch extra paths with --watching (VirtusLab#4174)

6c20fe0

Merge pull request VirtusLab#4177 from Gedochao/dx/contributions

2c22e11

Add LLM policy & a PR template

Use targeted Java/Scala mappings with the doc sub-command (VirtusLa…

bdaa4f4

…b#4180)

Correct Native test bridge error message and parse META-INF service f…

c1d45d7

…ile by lines to improve framework discovery (VirtusLab#4185)

Bump coursier to 2.1.25-M24 (VirtusLab#4184)

ab8f4b9

Add support for --cross in the doc sub-command (VirtusLab#4183)

4c529d6

Warn when .java & .scala sources are used in a mixed compilation …

7df6c78

…with disabled build server (VirtusLab#4181)

Add AGENTS.md & agentskills for directives & integration tests (Vir…

2352850

…tusLab#4178)

Add support for local .m2 in publish local (VirtusLab#4179)

5ed4f79

lostflydev force-pushed the scala-wasm-support branch from 80fe137 to 40df564 Compare March 18, 2026 11:05

Add release notes for Scala CLI v1.12.5 (VirtusLab#4190)

1491ac3

lostflydev force-pushed the scala-wasm-support branch from 40df564 to f138e4c Compare March 22, 2026 08:30

github-actions Bot and others added 2 commits March 22, 2026 16:38

Update scala-cli.sh launcher for 1.12.5 (VirtusLab#4191)

57cff2e

Co-authored-by: gh-actions <actions@github.com>

Bump Scala 3 Next RC to 3.8.3-RC3 (VirtusLab#4194)

0b036e5

Gedochao and others added 26 commits June 1, 2026 19:42

Bump Bloop to 2.1.0 (was 2.0.19) (VirtusLab#4295)

87910ff

Bump jsoup to 1.22.2 (was 1.22.1)

c255949

Bump jsoniter-scala to 2.38.14 (was 2.38.8)

09c2a11

Bump scalaMeta to 4.17.0 (was 4.15.2)

14c3931

Bump asm to 9.10.1 (was 9.9.1)

d40bdf3

Bump javaSemanticdb to 0.12.3 (was 0.10.0)

dc1b797

Bump scalafix to 0.14.6 (was 0.14.5)

71af093

Bump guava to 33.6.0-jre (was 33.5.0-jre)

5166cb8

Bump jgit to 7.6.0.202603022253-r (was 7.5.0.202512021534-r)

c742bad

Bump scalaPackager to 0.2.2 (was 0.2.1)

bc25a2d

Bump metaconfig-typesafe-config to 0.18.6 (was 0.18.2)

41f7933

Bump scalajs-env-nodejs to 1.6.0 (was 1.5.0)

c7d29b7

Bump pprint to 0.9.6 (was 0.9.5)

2f886d1

Bump sbt to 1.12.5 (was 1.12.4)

d450005

Bump mavenScalaCompilerPlugin to 4.9.10 (was 4.9.1)

0fe026d

Bump munit to 1.3.0 (was 1.2.2)

756b686

Restore SbtFile and null guards in JVM sourceFiles match

eabfdbe

Lost during Run.scala restructure for Wasm: restores the original case _: SbtFile => "" and case null => "" branches so SbtFile inputs are properly filtered from scala.sources JVM property.

lostflydev force-pushed the scala-wasm-support branch 2 times, most recently from c75c0c8 to d494c98 Compare June 6, 2026 19:11

lostflydev force-pushed the scala-wasm-support branch from d494c98 to 6c6eb57 Compare June 7, 2026 14:02

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Add WASM support: --wasm flag with Node.js and Deno runtimes#1

Add WASM support: --wasm flag with Node.js and Deno runtimes#1
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lostflydev commented Mar 6, 2026

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lostflydev commented Mar 6, 2026

What's added

Runtime support

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