Fix effectFnImplicitAny union context handling (#703)

Author: mattiamanzati

.changeset/fix-effect-fn-implicit-any-union-context.md

@@ -0,0 +1,7 @@
+---
+"@effect/language-service": patch
+---
+
+Fix `effectFnImplicitAny` so it does not report false positives when an `Effect.fn` or `Effect.fnUntraced` callback gets its contextual function type from a union member.
+
+For example, nested `HttpRouter.add(...)` handlers now correctly recognize the inferred `request` type and produce no diagnostics when the parameter is not actually implicit `any`.

packages/harness-effect-v4/__snapshots__/diagnostics/effectFnImplicitAny_noDiags.ts.codefixes

@@ -0,0 +1 @@
+no codefixes

packages/harness-effect-v4/__snapshots__/diagnostics/effectFnImplicitAny_noDiags.ts.output

@@ -0,0 +1 @@
+// no diagnostics

packages/harness-effect-v4/examples/diagnostics/effectFnImplicitAny_noDiags.ts

@@ -0,0 +1,15 @@
+// @effect-diagnostics effectFnImplicitAny:error
+import * as Effect from "effect/Effect"
+import { HttpRouter, HttpServerResponse } from "effect/unstable/http"
+
+export const Route = HttpRouter.use(
+    Effect.fnUntraced(function*(router){
+        yield* router.add(
+            "GET",
+            "/",
+            Effect.fnUntraced(function*(request){
+                return HttpServerResponse.empty()
+            })
+        )
+    })
+)

packages/language-service/src/diagnostics/effectFnImplicitAny.ts

@@ -3,6 +3,7 @@ import type ts from "typescript"
 import * as LSP from "../core/LSP.js"
 import * as Nano from "../core/Nano.js"
 import * as TypeCheckerApi from "../core/TypeCheckerApi.js"
+import * as TypeCheckerUtils from "../core/TypeCheckerUtils.js"
 import * as TypeParser from "../core/TypeParser.js"
 import * as TypeScriptApi from "../core/TypeScriptApi.js"
 
@@ -23,13 +24,16 @@ const getParameterName = (typescript: TypeScriptApi.TypeScriptApi, name: ts.Bind
 const hasOuterContextualFunctionType = (
   typescript: TypeScriptApi.TypeScriptApi,
   typeChecker: ts.TypeChecker,
+  typeCheckerUtils: TypeCheckerUtils.TypeCheckerUtils,
   node: ts.CallExpression
 ): boolean => {
   const contextualType = typeChecker.getContextualType(node)
   if (!contextualType) {
     return false
   }
-  return typeChecker.getSignaturesOfType(contextualType, typescript.SignatureKind.Call).length > 0
+  return typeCheckerUtils.unrollUnionMembers(contextualType).some((type) =>
+    typeChecker.getSignaturesOfType(type, typescript.SignatureKind.Call).length > 0
+  )
 }
 
 export const effectFnImplicitAny = LSP.createDiagnostic({
@@ -45,6 +49,7 @@ export const effectFnImplicitAny = LSP.createDiagnostic({
     const ts = yield* Nano.service(TypeScriptApi.TypeScriptApi)
     const program = yield* Nano.service(TypeScriptApi.TypeScriptProgram)
     const typeChecker = yield* Nano.service(TypeCheckerApi.TypeCheckerApi)
+    const typeCheckerUtils = yield* Nano.service(TypeCheckerUtils.TypeCheckerUtils)
     const typeParser = yield* Nano.service(TypeParser.TypeParser)
 
     const noImplicitAny = program.getCompilerOptions().noImplicitAny ?? program.getCompilerOptions().strict ?? false
@@ -89,7 +94,7 @@ export const effectFnImplicitAny = LSP.createDiagnostic({
         Nano.orUndefined
       )
 
-      if (!parsed || hasOuterContextualFunctionType(ts, typeChecker, parsed.call)) {
+      if (!parsed || hasOuterContextualFunctionType(ts, typeChecker, typeCheckerUtils, parsed.call)) {
         continue
       }