An IntelliJ plugin that replaces IntelliJ's Scala type backend with the real Scala 3 compiler.
Pre-alpha. The replacement backend is implemented and undergoing its final compatibility and regression graduation.
Metallurgy runs the module's real Scala 3 presentation compiler through Scalameta's published interfaces and exposes its types and symbols through the existing Scala PSI model. IntelliJ keeps its editor, project import, build, test, debugger, and refactoring infrastructure while Scala 3 supplies the semantic backend.
Compiler-backed types, symbol resolution, completion, hover, inline hints, navigation, and best-effort cross-module operation are working. The implementation is tested against substantial Scala 3 codebases including Cats, Cats Effect, ZIO, Shapeless 3, Tapir, and FS2.
Metallurgy replaces IntelliJ's Scala type backend with the real Scala 3 compiler — so it can do things the bundled
plugin can't. For example, named type arguments ([A = Int]):
| Bundled Scala plugin (before) | Metallurgy (after) |
|---|---|
 |
 |
| Status | Area | Current state |
|---|---|---|
| ✅ | Compiler integration | Resolves each module's presentation compiler through published Scalameta interfaces and discovers optional capabilities without version allowlists. |
| ✅ | Type resolution | Whole-file compiler snapshots provide expression, declaration, binding, function, parameter, pattern, expected, widened, and exact types. |
| ✅ | Freshness and isolation | Document-version guards, generation retirement, per-element invalidation, and inactive-module no-op behavior are covered by tests. |
| ✅ | Resolve and navigation | Compiler symbols map to stable source PSI or generation-scoped light PSI for compiler-only declarations. |
| ✅ | IDE presentation | Completion, hover, Quick Documentation, inline hints, parameter information, navigation, inspections, search, and representative refactorings consume compiler results. |
| ✅ | Best-effort compilation | BETASTY capabilities, broken-upstream-module consumption, artifact freshness, and classpath/session replacement are implemented. |
| ✅ | Project loading | IntelliJ's native sbt and BSP loaders remain intact and feed the same loader-neutral compiler-backend pipeline. |
| ✅ | Worksheets | Physical Scala worksheets use the normal versioned compiler backend while the bundled plugin retains execution and result transport. |
| ✅ | Applications and tests | Scala 3 main, @main, ScalaTest, MUnit, Specs2, and uTest discovery/configuration continue through bundled run infrastructure. |
| ✅ | Ecosystem projects | Pinned Cats, Cats Effect, ZIO, Shapeless 3, Tapir, and FS2 revisions compile cleanly; representative compiler-to-PSI semantic facts pass. |
| Debugger fragments | Synthetic debugger expressions deliberately use the bundled evaluator because they do not have a safe source-document generation key. | |
| Interactive REPL console | Physical worksheet semantics are compiler-backed; synthetic console input remains an explicit bundled fallback. | |
| Platform UAST discovery | Direct Scala UAST conversion inherits compiler results, but the bundled UAST language plugin is unavailable while the compiler-highlighting failsafe is active. | |
| ⏳ | Final graduation | The complete Metallurgy suite, all Scala 3-focused intellij-scala tests, aggregate latency/memory evidence, and the final go/no-go report remain in #60. |
The idea — running the Scala compiler directly inside IntelliJ, without LSP — comes from Jędrzej Rochala's ScalaWAW #32 talk (The best Scala IDE inside your favourite Scala IDE).
- IntelliJ IDEA 2026.1+ with the Scala plugin
- A Scala 3 project
sbt packageArtifactZipThen Settings | Plugins | Install plugin from disk… → the zip in target/.
sbt compile # build
sbt test # run tests
sbt runIDE # dev IDEA with the plugin loaded
sbt fmt | sbt check # format / verify (CI gate)See CONTRIBUTING.md and AGENTS.md.
docs/scala3-compiler-backend.md— the architecture and reference- Epic #73 — the PSI-producer target architecture and implementation plan
Apache License 2.0 — see LICENSE.