Add LanguageService to rules context

CHANGELOG.md

@@ -2,7 +2,13 @@
 
 ## Unreleased
 
-- Deprecate `context.rawChecker`. Types overrides from `context.checker` have been updated so it can be passed to other libraries. Thanks @JoshuaKGoldberg for challenging this!
+### Add `context.languageService`
+
+This allows to create a first kind of 'multi-file' rules. It's used in the new core rule `core/unusedExport`.
+
+### Deprecate `context.rawChecker`
+
+Types overrides of `context.checker` have been updated so it can be passed to other libraries. `context.rawChecker` is therefore not needed anymore and has been deprecated. Thanks @JoshuaKGoldberg for challenging this!
 
 ## 1.0.28
 

README.md

@@ -273,7 +273,13 @@ export default defineConfig({
 
 ## Core rules
 
-Currently, the list of core rules are the type-aware lint rules I use from typescript-eslint. If you think more rules should be added, please open an issue, but to reduce the surface, only non-styling type-aware rules will be accepted. Here is the list of [typescript-eslint type aware rules](https://typescript-eslint.io/rules/?=typeInformation) with their status:
+### Exclusive rules
+
+- unusedExport: Detect unused exports
+
+### From typescript-eslint
+
+Currently, the ported rules are the type-aware lint rules I use from typescript-eslint. If you think more rules should be added, please open an issue, but to reduce the surface, only non-styling type-aware rules will be accepted. Here is the list of [typescript-eslint type aware rules](https://typescript-eslint.io/rules/?=typeInformation) with their status:
 
 - await-thenable: ✅ Implemented
 - consistent-return: 🛑 Implementation not planned, you can use `noImplicitReturns` compilerOption

package.json

@@ -13,7 +13,7 @@
     "import": "bun scripts/import-rule.ts",
     "test": "bun test",
     "build": "bun scripts/bundle.ts && tsc -p tsconfig.dist.json && cd dist && publint",
-    "tsl": "bun src/cli.ts",
+    "tsl": "bun src/cli-entrypoint.ts",
     "prettier-all": "bun prettier-ci --write",
     "prettier-ci": "prettier --cache --check '**/*.{ts,json,md,yml}'",
     "check": "bun prettier-ci && bun run test && bun tsl && bun run build",

src/cli.ts

@@ -7,6 +7,7 @@ import {
   formatDiagnostics,
   type TSLDiagnostic,
 } from "./formatDiagnostic.ts";
+import { getLanguageService } from "./getLanguageService.ts";
 import { core } from "./index.ts";
 import { initRules } from "./initRules.ts";
 import { loadConfig } from "./loadConfig.ts";
@@ -62,12 +63,14 @@ if (result.errors.length) {
 }
 
 const host = ts.createCompilerHost(result.options, true);
-const program = ts.createProgram({
+const programForLanguageServiceHost = ts.createProgram({
   rootNames: result.fileNames,
   options: result.options,
   projectReferences: result.projectReferences,
-  host,
+  host: host,
 });
+const languageService = getLanguageService(programForLanguageServiceHost);
+const program = languageService.getProgram()!;
 
 if (values.timing) {
   console.log(`TS program created in ${displayTiming(programStart)}`);
@@ -77,6 +80,7 @@ const configStart = performance.now();
 const { config } = await loadConfig(program);
 const { lint, allRules, timingMaps } = await initRules(
   () => program,
+  () => languageService,
   config ?? { rules: core.all() },
   values.timing,
 );

src/formatDiagnostic.ts

@@ -179,7 +179,7 @@ function formatCodeSpan(
   return context;
 }
 
-export function formatLocation(file: SourceFile, start: number): string {
+function formatLocation(file: SourceFile, start: number): string {
   const { line, character } = getLineAndCharacterOfPosition(file, start);
   const relativeFileName = displayFilename(file.fileName);
   let output = "";

src/getLanguageService.ts

@@ -0,0 +1,30 @@
+import fs from "node:fs";
+import ts from "typescript";
+
+export const getLanguageService = (
+  program: ts.Program,
+  overridesForTesting?: {
+    readFile: (path: string) => string | undefined;
+    fileExists: (path: string) => boolean;
+    directoryExists: (path: string) => boolean;
+  },
+) => {
+  const languageServiceHost: ts.LanguageServiceHost = {
+    getCompilationSettings: () => program.getCompilerOptions(),
+    getScriptFileNames: () => program.getSourceFiles().map((f) => f.fileName),
+    getScriptVersion: () => "",
+    getScriptSnapshot: (fileName) => {
+      const sourceFile = program.getSourceFile(fileName);
+      if (!sourceFile) return undefined;
+      return ts.ScriptSnapshot.fromString(sourceFile.text);
+    },
+    getCurrentDirectory: () => process.cwd(),
+    getDefaultLibFileName: ts.getDefaultLibFileName,
+    readFile: (path, encoding) =>
+      overridesForTesting?.readFile(path)
+      ?? fs.readFileSync(path, encoding as BufferEncoding),
+    fileExists: overridesForTesting?.fileExists ?? fs.existsSync,
+    directoryExists: overridesForTesting?.directoryExists,
+  };
+  return ts.createLanguageService(languageServiceHost);
+};

src/getPlugin.ts

@@ -38,6 +38,7 @@ export const getPlugin = async (
     }
     const result = await initRules(
       () => languageService.getProgram()!,
+      () => languageService,
       config ?? { rules: [] },
       false,
     );

src/index.ts

@@ -32,8 +32,10 @@ import { restrictTemplateExpressions } from "./rules/restrictTemplateExpressions
 import { returnAwait } from "./rules/returnAwait/returnAwait.ts";
 import { strictBooleanExpressions } from "./rules/strictBooleanExpressions/strictBooleanExpressions.ts";
 import { switchExhaustivenessCheck } from "./rules/switchExhaustivenessCheck/switchExhaustivenessCheck.ts";
+import { unusedExport } from "./rules/unusedExport/unusedExport.ts";
 import type { Config, Rule } from "./types.ts";
 
+/* tsl-ignore core/unusedExport */
 export type {
   AST,
   Checker,
@@ -96,4 +98,5 @@ export const core = createRulesSet({
   returnAwait,
   strictBooleanExpressions,
   switchExhaustivenessCheck,
+  unusedExport,
 });

src/initRules.ts

@@ -29,6 +29,7 @@ const run = <T>(cb: () => T) => cb();
 
 export const initRules = async (
   getProgram: () => ts.Program,
+  getLanguageService: () => ts.LanguageService,
   config: Config,
   showTiming: boolean,
 ) => {
@@ -98,6 +99,9 @@ export const initRules = async (
           get program() {
             return getProgram();
           },
+          get languageService() {
+            return getLanguageService();
+          },
           get checker() {
             return getProgram().getTypeChecker() as unknown as Checker;
           },

src/loadConfig.ts

@@ -74,7 +74,7 @@ export const loadConfig = async (
   };
 };
 
-export const findConfigPath = (program: ts.Program) => {
+const findConfigPath = (program: ts.Program) => {
   let dir = program.getCurrentDirectory();
   const { root } = path.parse(dir);
   let configPath: string | undefined = undefined;