refactor: Correct a few minor bugs

Author: nonara

src/resolve/resolve-module-name.ts

@@ -3,8 +3,8 @@ import {
   baseName, dirName, isBaseDir, isURL, joinPaths, maybeAddRelativeLocalPrefix, normalizeSlashes, relativePath,
   removeSuffix
 } from "../utils";
-import { getOutputExtension, Node, Pattern, removeFileExtension, ResolvedModuleFull, SourceFile } from "typescript";
-import { getOutputPathForSourceFile } from "../ts";
+import { Node, Pattern, removeFileExtension, ResolvedModuleFull, SourceFile } from "typescript";
+import { getOutputPathForSourceFile, getOutputExtension } from "../ts";
 import { getOutputPathDetail, OutputPathDetail } from "./output-path-detail";
 import { IndexFlags } from "./index-checker";
 
@@ -63,6 +63,8 @@ function getReturnPath(ctx: GetReturnPathContext) {
     resolver,
     config: { outputExtensions, outputIndexes },
     compilerOptions,
+    tsInstance,
+    isDeclarationFile
   } = ctx.visitorContext;
   const { suppliedExt, resolvedPath, isImplicitExtension, indexDetail, isExternalLibraryImport } = ctx.pathDetail ?? {};
 
@@ -74,7 +76,7 @@ function getReturnPath(ctx: GetReturnPathContext) {
       !isImplicitExtension && outputExtensions !== 'never'
         ? suppliedExt
         : outputExtensions === 'always'
-        ? getOutputExtension(resolvedSourceFile!, compilerOptions)
+        ? getOutputExtension(tsInstance, compilerOptions, resolvedSourceFile!, isDeclarationFile)
         : void 0;
 
     let usesStrippedIndex = false;

src/ts/ts-helpers.ts

@@ -137,4 +137,13 @@ export function checkTsSupport(tsInstance: typeof TS) {
     throw new Error(`The latest version of 'typescript-transform-paths' requires TS version 4.2.2 or higher. Either upgrade TS or use v3 of the plugin.`);
 }
 
+export function getOutputExtension(
+  tsInstance: typeof TS,
+  compilerOptions: TS.CompilerOptions,
+  sourceFile: TS.SourceFile,
+  isDeclaration: boolean
+) {
+  return isDeclaration ? '.d.ts' : tsInstance.getOutputExtension(sourceFile, compilerOptions);
+}
+
 // endregion

src/utils.ts

@@ -31,8 +31,8 @@ export const maybeAddRelativeLocalPrefix = (p: string) => (p[0] === "." ? p : `.
  * Merge and normalize paths (preserves relative prefix – ie. `./my/path`)
  */
 export function joinPaths(...paths: (string | undefined)[]): string {
-  // path.join / ts.normalizePath cannot be used here, because they remove relative prefix
-  return normalizePath((paths.filter(p => !!p) as string[]).join('/'))!;
+  // path.join / normalizePath cannot be used here, because they remove relative prefix
+  return normalizeSlashes((paths.filter(p => !!p) as string[]).join('/'))!;
 }
 
 /**