Effect Language Service (TypeScript-Go)

A wrapper around TypeScript-Go that builds the Effect Language Service, providing Effect-TS diagnostics and quick fixes. This project targets Effect V4 (codename: "smol") primarily and also Effect V3.

Currently in Alpha

The TypeScript-Go version of the Effect LSP should be considered in Alpha. Expect breaking changes between releases and some missing features compared to previous version. Some of them are currently on hold due to not yet complete pipeline on the upstream TypeScript repository.

Installation

The setup of the TSGO version of the LSP can be performed via the command line interface:

npx @effect/tsgo setup

This will guide you through the installation process, which includes:

1. Adding the @effect/tsgo dependency to your project.
2. Configuring your tsconfig.json to use the Effect Language Service plugin.
3. Adjusting plugin options to your preference.
4. Hinting at any additional editor configuration needed to ensure the LSP is active.

Diagnostic Status

Some diagnostics are off by default or have a default severity of suggestion, but you can always enable them or change their default severity in the plugin options.

Diagnostic	Sev	Fix	Description	v3	v4
Correctness Wrong, unsafe, or structurally invalid code patterns.
anyUnknownInErrorContext	➖		Detects 'any' or 'unknown' types in Effect error or requirements channels	✓	✓
classSelfMismatch	❌	🔧	Ensures Self type parameter matches the class name in ServiceMap/Service/Tag/Schema classes	✓	✓
duplicatePackage	⚠️		Warns when multiple versions of an Effect-related package are detected in the program	✓	✓
effectFnImplicitAny	❌		Mirrors noImplicitAny for unannotated Effect.fn, Effect.fnUntraced, and Effect.fnUntracedEager callback parameters when no outer contextual function type exists. Requires TS's noImplicitAny: true	✓	✓
floatingEffect	❌		Detects Effect values that are neither yielded nor assigned	✓	✓
genericEffectServices	⚠️		Prevents services with type parameters that cannot be discriminated at runtime	✓	✓
missingEffectContext	❌		Detects Effect values with unhandled context requirements	✓	✓
missingEffectError	❌	🔧	Detects Effect values with unhandled error types	✓	✓
missingLayerContext	❌		Detects Layer values with unhandled context requirements	✓	✓
missingReturnYieldStar	❌	🔧	Suggests using return yield* for Effects that never succeed	✓	✓
missingStarInYieldEffectGen	❌	🔧	Detects bare yield (without *) inside Effect generator scopes	✓	✓
nonObjectEffectServiceType	❌		Ensures Effect.Service types are objects, not primitives	✓
outdatedApi	⚠️		Detects usage of APIs that have been removed or renamed in Effect v4		✓
overriddenSchemaConstructor	❌	🔧	Prevents overriding constructors in Schema classes which breaks decoding behavior	✓	✓
Anti-pattern Discouraged patterns that often lead to bugs or confusing behavior.
catchUnfailableEffect	💡		Warns when using error handling on Effects that never fail	✓	✓
effectFnIife	⚠️	🔧	Effect.fn or Effect.fnUntraced is called as an IIFE; use Effect.gen instead	✓	✓
effectGenUsesAdapter	⚠️		Warns when using the deprecated adapter parameter in Effect.gen	✓	✓
effectInFailure	⚠️		Warns when an Effect is used inside an Effect failure channel	✓	✓
effectInVoidSuccess	⚠️		Detects nested Effects in void success channels that may cause unexecuted effects	✓	✓
globalErrorInEffectCatch	⚠️		Warns when catch callbacks return global Error type instead of typed errors	✓	✓
globalErrorInEffectFailure	⚠️		Warns when the global Error type is used in an Effect failure channel	✓	✓
layerMergeAllWithDependencies	⚠️	🔧	Detects interdependencies in Layer.mergeAll calls where one layer provides a service that another layer requires	✓	✓
leakingRequirements	💡		Detects implementation services leaked in service methods	✓	✓
multipleEffectProvide	⚠️	🔧	Warns against chaining Effect.provide calls which can cause service lifecycle issues	✓	✓
returnEffectInGen	💡	🔧	Warns when returning an Effect in a generator causes nested Effect<Effect<...>>	✓	✓
runEffectInsideEffect	💡	🔧	Suggests using Runtime methods instead of Effect.run* inside Effect contexts	✓
schemaSyncInEffect	💡		Suggests using Effect-based Schema methods instead of sync methods inside Effect generators	✓
scopeInLayerEffect	⚠️	🔧	Suggests using Layer.scoped instead of Layer.effect when Scope is in requirements	✓
strictEffectProvide	➖		Warns when using Effect.provide with layers outside of application entry points	✓	✓
tryCatchInEffectGen	💡		Discourages try/catch in Effect generators in favor of Effect error handling	✓	✓
unknownInEffectCatch	⚠️		Warns when catch callbacks return unknown instead of typed errors	✓	✓
Effect-native Prefer Effect-native APIs and abstractions when available.
extendsNativeError	➖		Warns when a class directly extends the native Error class	✓	✓
globalFetch	➖		Warns when using the global fetch function instead of the Effect HTTP client	✓	✓
instanceOfSchema	➖	🔧	Suggests using Schema.is instead of instanceof for Effect Schema types	✓	✓
nodeBuiltinImport	➖		Warns when importing Node.js built-in modules that have Effect-native counterparts	✓	✓
preferSchemaOverJson	💡		Suggests using Effect Schema for JSON operations instead of JSON.parse/JSON.stringify	✓	✓
Style Cleanup, consistency, and idiomatic Effect code.
catchAllToMapError	💡	🔧	Suggests using Effect.mapError instead of Effect.catch + Effect.fail	✓	✓
deterministicKeys	➖	🔧	Enforces deterministic naming for service/tag/error identifiers based on class names	✓	✓
effectFnOpportunity	💡	🔧	Suggests using Effect.fn for functions that return an Effect	✓	✓
effectMapVoid	💡	🔧	Suggests using Effect.asVoid instead of Effect.map(() => void 0), Effect.map(() => undefined), or Effect.map(() => {})	✓	✓
effectSucceedWithVoid	💡	🔧	Suggests using Effect.void instead of Effect.succeed(undefined) or Effect.succeed(void 0)	✓	✓
missedPipeableOpportunity	➖	🔧	Suggests using .pipe() for nested function calls	✓	✓
missingEffectServiceDependency	➖		Checks that Effect.Service dependencies satisfy all required layer inputs	✓
redundantSchemaTagIdentifier	💡	🔧	Suggests removing redundant identifier argument when it equals the tag value in Schema.TaggedClass/TaggedError/TaggedRequest	✓	✓
schemaStructWithTag	💡	🔧	Suggests using Schema.TaggedStruct instead of Schema.Struct with _tag field	✓	✓
schemaUnionOfLiterals	➖	🔧	Suggests combining multiple Schema.Literal calls in Schema.Union into a single Schema.Literal	✓
serviceNotAsClass	➖	🔧	Warns when ServiceMap.Service is used as a variable instead of a class declaration		✓
strictBooleanExpressions	➖		Enforces boolean types in conditional expressions for type safety	✓	✓
unnecessaryEffectGen	💡	🔧	Suggests removing Effect.gen when it contains only a single return statement	✓	✓
unnecessaryFailYieldableError	💡	🔧	Suggests yielding yieldable errors directly instead of wrapping with Effect.fail	✓	✓
unnecessaryPipe	💡	🔧	Removes pipe calls with no arguments	✓	✓
unnecessaryPipeChain	💡	🔧	Simplifies chained pipe calls into a single pipe call	✓	✓

➖ off by default, ❌ error, ⚠️ warning, 💬 message, 💡 suggestion, 🔧 quick fix available

Refactor Status

Refactor	V3	V4	Notes
asyncAwaitToFn	✅	✅	Convert async/await to Effect.fn
asyncAwaitToFnTryPromise	✅	✅	Convert async/await to Effect.fn with Error ADT + tryPromise
asyncAwaitToGen	✅	✅	Convert async/await to Effect.gen
asyncAwaitToGenTryPromise	✅	✅	Convert async/await to Effect.gen with Error ADT + tryPromise
debugPerformance	❌	❌	Insert performance timing debug comments
effectGenToFn	✅	✅	Convert Effect.gen to Effect.fn
functionToArrow	✅	✅	Convert function declaration to arrow function
layerMagic	✅	✅	Auto-compose layers with correct merge/provide
makeSchemaOpaque	✅	✅	Convert Schema to opaque type aliases
makeSchemaOpaqueWithNs	✅	✅	Convert Schema to opaque types with namespace
pipeableToDatafirst	✅	✅	Convert pipeable calls to data-first style
removeUnnecessaryEffectGen	✅	✅	Remove redundant Effect.gen wrapper
structuralTypeToSchema	✅	✅	Generate recursive Schema from type alias
toggleLazyConst	✅	✅	Toggle lazy/eager const declarations
togglePipeStyle	✅	✅	Toggle pipe(x, f) vs x.pipe(f)
toggleReturnTypeAnnotation	✅	✅	Add/remove return type annotation
toggleTypeAnnotation	✅	✅	Add/remove variable type annotation
typeToEffectSchema	✅	✅	Generate Effect.Schema from type alias
typeToEffectSchemaClass	✅	✅	Generate Schema.Class from type alias
wrapWithEffectGen	✅	✅	Wrap expression in Effect.gen
wrapWithPipe	❌	✅	Wrap selection in pipe(...)
writeTagClassAccessors	✅	➖	Generate static accessors for Effect.Service/Tag classes

Completion Status

Completion	V3	V4	Notes
contextSelfInClasses	✅	➖	Context.Tag self-type snippets in extends clauses (V3-only)
effectDataClasses	✅	✅	Data class constructor snippets in extends clauses
effectSchemaSelfInClasses	✅	✅	Schema/Model class constructor snippets in extends clauses
effectSelfInClasses	✅	➖	Effect.Service/Effect.Tag self-type snippets in extends clauses (V3-only)
genFunctionStar	✅	✅	gen(function*(){}) snippet when dot-accessing .gen on objects with callable gen property
effectCodegensComment	✅	✅	@effect-codegens directive snippet in comments with codegen name choices
effectDiagnosticsComment	✅	✅	@effect-diagnostics / @effect-diagnostics-next-line directive snippets in comments
rpcMakeClasses	✅	➖	Rpc.make constructor snippet in extends clauses (V3-only)
schemaBrand	✅	➖	brand("varName") snippet when dot-accessing Schema in variable declarations (V3-only)
serviceMapSelfInClasses	✅	✅	Service map self-type snippets in extends clauses

Codegen Status

Codegen	V3	V4	Notes
accessors	❌	❌	Generate Service accessor methods from comment directive
annotate	❌	❌	Generate type annotations from comment directive
typeToSchema	❌	❌	Generate Schema from type alias comment directive

Rename Status

Rename	V3	V4	Notes
keyStrings	❌	❌	Extend rename to include key string literals in Effect classes

Best Practices

Relationship to Official TypeScript-Go (tsgo)

Effect-tsgo is a superset of the official TypeScript-Go — it embeds a pinned version of tsgo with a small patch set on top and adds the Effect language service. This means effect-tsgo provides all standard TypeScript-Go functionality plus Effect-specific diagnostics, quick fixes, and refactors.

Use effect-tsgo instead of tsgo, not alongside it. Running both in parallel will produce duplicate diagnostics and degrade editor performance. Configure your editor to use effect-tsgo as your sole TypeScript language server.

Version Pinning

Each release of effect-tsgo is built against a specific upstream tsgo commit. The pinned commit is recorded in flake.nix (typescript-go-src). When upstream tsgo releases new features or fixes, effect-tsgo will adopt them in a subsequent release after validating compatibility with the Effect diagnostics layer.

When to Upgrade

• Upgrade effect-tsgo when a new release includes upstream tsgo fixes you need or new Effect diagnostics you want.
• There is no need to track upstream tsgo releases separately — effect-tsgo is the single binary to manage.

Plugin Options

{
  "compilerOptions": {
    "plugins": [
      {
        "name": "@effect/language-service",
        // Maps rule names to severity levels. Use {} to enable diagnostics with rule defaults. (default: {})
        "diagnosticSeverity": {},
        // When false, suggestion-level Effect diagnostics are omitted from tsc CLI output. (default: true)
        "includeSuggestionsInTsc": true,
        // When true, suggestion diagnostics do not affect the tsc exit code. (default: true)
        "ignoreEffectSuggestionsInTscExitCode": true,
        // When true, warning diagnostics do not affect the tsc exit code. (default: false)
        "ignoreEffectWarningsInTscExitCode": false,
        // When true, error diagnostics do not affect the tsc exit code. (default: false)
        "ignoreEffectErrorsInTscExitCode": false,
        // When true, disabled diagnostics are still processed so directives can re-enable them. (default: false)
        "skipDisabledOptimization": false,
        // Configures key pattern formulas for the deterministicKeys rule. (default: [{"target":"service","pattern":"default","skipLeadingPath":["src/"]},{"target":"custom","pattern":"default","skipLeadingPath":["src/"]}])
        "keyPatterns": [
          {
            "target": "service",
            "pattern": "default",
            "skipLeadingPath": [
              "src/"
            ]
          },
          {
            "target": "custom",
            "pattern": "default",
            "skipLeadingPath": [
              "src/"
            ]
          }
        ],
        // Enables matching constructors with @effect-identifier annotations. (default: false)
        "extendedKeyDetection": false,
        // Minimum number of contiguous pipeable transformations to trigger missedPipeableOpportunity. (default: 2)
        "pipeableMinArgCount": 2,
        // Mermaid rendering service for layer graph links. Accepts mermaid.live, mermaid.com, or a custom URL. (default: "mermaid.live")
        "mermaidProvider": "mermaid.live",
        // When true, suppresses external Mermaid links in hover output. (default: false)
        "noExternal": false,
        // How many levels deep the layer graph extraction follows symbol references. (default: 0)
        "layerGraphFollowDepth": 0,
        // Controls which effectFnOpportunity quickfix variants are offered. (default: ["span"])
        "effectFn": [
          "span"
        ],
        // When true, suppresses redundant return-type inlay hints on supported Effect generator functions. (default: false)
        "inlays": false,
        // Package names allowed to have multiple versions without triggering duplicatePackage. (default: [])
        "allowedDuplicatedPackages": [],
        // Package names that should prefer namespace imports. (default: [])
        "namespaceImportPackages": [],
        // Package names that should prefer barrel named imports. (default: [])
        "barrelImportPackages": [],
        // Package-level import aliases keyed by package name. (default: {})
        "importAliases": {},
        // Controls whether named reexports are followed at package top-level. (default: "ignore")
        "topLevelNamedReexports": "ignore"
      }
    ]
  }
}