Start using resolve as the default module resolver

packages/knip/package.json

@@ -74,6 +74,7 @@
     "picocolors": "1.0.0",
     "picomatch": "4.0.1",
     "pretty-ms": "9.0.0",
+    "resolve": "1.22.8",
     "smol-toml": "1.1.4",
     "strip-json-comments": "5.0.1",
     "summary": "2.1.0",
@@ -96,6 +97,7 @@
     "@types/minimist": "^1.2.5",
     "@types/npmcli__map-workspaces": "^3.0.4",
     "@types/npmcli__package-json": "^4.0.4",
+    "@types/resolve": "1.20.6",
     "@types/webpack": "^5.28.5",
     "c8": "9.1.0",
     "eslint": "^8.57.0",

packages/knip/src/typescript/resolveModuleNames.ts

@@ -1,8 +1,10 @@
 import { existsSync } from 'node:fs';
 import { isBuiltin } from 'node:module';
+import resolve from 'resolve';
 import ts from 'typescript';
+import { DEFAULT_EXTENSIONS } from '../constants.js';
 import { sanitizeSpecifier } from '../util/modules.js';
-import { dirname, extname, isAbsolute, isInNodeModules, isInternal, join } from '../util/path.js';
+import { dirname, extname, isAbsolute, isInNodeModules, isInternal, join, toPosix } from '../util/path.js';
 import { isDeclarationFileExtension } from './ast-helpers.js';
 import { ensureRealFilePath, isVirtualFilePath } from './utils.js';
 
@@ -25,6 +27,8 @@ export function createCustomModuleResolver(
   compilerOptions: ts.CompilerOptions,
   virtualFileExtensions: string[]
 ) {
+  const extensions = [...DEFAULT_EXTENSIONS, ...virtualFileExtensions];
+
   function resolveModuleNames(moduleNames: string[], containingFile: string): Array<ts.ResolvedModuleFull | undefined> {
     return moduleNames.map(moduleName => {
       const key = moduleName.startsWith('.')
@@ -43,6 +47,27 @@ export function createCustomModuleResolver(
     // No need to try and resolve builtins or externals, bail out
     if (isBuiltin(sanitizedSpecifier) || isInNodeModules(name)) return undefined;
 
+    try {
+      const resolved = resolve.sync(sanitizedSpecifier, {
+        basedir: dirname(containingFile),
+        extensions,
+        preserveSymlinks: false,
+      });
+
+      const resolvedFileName = toPosix(resolved);
+      const ext = extname(resolved);
+      const extension = virtualFileExtensions.includes(ext) ? ts.Extension.Js : ext;
+
+      return {
+        resolvedFileName,
+        extension,
+        isExternalLibraryImport: isInNodeModules(resolvedFileName),
+        resolvedUsingTsExtension: false,
+      };
+    } catch (err) {
+      // Intentional slip-through, plenty of cases left in TS context
+    }
+
     const tsResolvedModule = ts.resolveModuleName(
       sanitizedSpecifier,
       containingFile,