fix: regard file extensions during path resolution (dividab#133)

Originally during the file path resolution, file extensions were removed
without explicit reason. This commit changes the resolution logic to keep file
extensions, with the goal to add support for modern non-js extensions
like cjs. The change however keeps /xyz/index resolves as is as they
still should resolve to /xyz.

Refs 847d314

Author: katywings

src/filesystem.ts

@@ -81,7 +81,3 @@ export function fileExistsAsync(
     callback2(undefined, stats ? stats.isFile() : false);
   });
 }
-
-export function removeExtension(path: string): string {
-  return path.substring(0, path.lastIndexOf(".")) || path;
-}

src/match-path-async.ts

@@ -148,7 +148,6 @@ function findFirstExistingPath(
         return doneCallback(err);
       }
       if (exists) {
-        // Not sure why we don't just return the full path? Why strip it?
         return doneCallback(undefined, TryPath.getStrippedPath(tryPath));
       }
       if (index === tryPaths.length - 1) {
@@ -180,11 +179,7 @@ function findFirstExistingPath(
               return doneCallback(mainFieldErr);
             }
             if (mainFieldMappedFile) {
-              // Not sure why we don't just return the full path? Why strip it?
-              return doneCallback(
-                undefined,
-                Filesystem.removeExtension(mainFieldMappedFile)
-              );
+              return doneCallback(undefined, mainFieldMappedFile);
             }
 
             // No field in package json was a valid option. Continue with the next path.

src/match-path-sync.ts

@@ -118,7 +118,6 @@ function findFirstExistingPath(
       tryPath.type === "index"
     ) {
       if (fileExists(tryPath.path)) {
-        // Not sure why we don't just return the full path? Why strip it?
         return TryPath.getStrippedPath(tryPath);
       }
     } else if (tryPath.type === "package") {
@@ -131,8 +130,7 @@ function findFirstExistingPath(
           fileExists
         );
         if (mainFieldMappedFile) {
-          // Not sure why we don't just return the full path? Why strip it?
-          return Filesystem.removeExtension(mainFieldMappedFile);
+          return mainFieldMappedFile;
         }
       }
     } else {

src/try-path.ts

@@ -1,7 +1,6 @@
 import * as path from "path";
 import { MappingEntry } from "./mapping-entry";
 import { dirname } from "path";
-import { removeExtension } from "./filesystem";
 
 export interface TryPath {
   readonly type: "file" | "extension" | "index" | "package";
@@ -60,15 +59,12 @@ export function getPathsToTry(
   return pathsToTry.length === 0 ? undefined : pathsToTry;
 }
 
-// Not sure why we don't just return the full found path?
 export function getStrippedPath(tryPath: TryPath): string {
   return tryPath.type === "index"
     ? dirname(tryPath.path)
-    : tryPath.type === "file"
-    ? tryPath.path
-    : tryPath.type === "extension"
-    ? removeExtension(tryPath.path)
-    : tryPath.type === "package"
+    : tryPath.type === "file" ||
+      tryPath.type === "extension" ||
+      tryPath.type === "package"
     ? tryPath.path
     : exhaustiveTypeException(tryPath.type);
 }