fix: resolve node_modules/package/dir/foo.js if node_modules/package/dir/foo/ exists (#896)

fixes #893
closes #894

PR #839 incorrectly assumed the specifier is always a package name, but
a specifier can be `package/dir/foo` where both
`node_modules/package/dir/foo.js` and `node_modules/package/dir/foo/`
exists.

Author: Boshen

fixtures/enhanced-resolve/test/fixtures/node_modules/@scope/dir-and-file/foo.js

@@ -932,7 +932,15 @@ impl<Fs: FileSystem> ResolverGeneric<Fs> {
                     return Ok(self.cache.is_dir(&cached_path, ctx).then(|| cached_path.clone()));
                 }
 
-                // Perf: try LOAD_AS_DIRECTORY first. No modern package manager creates `node_modules/X.js`.
+                // Only load the file if it is targeting a `X/sub/dir`.
+                if specifier != package_name
+                    && !specifier.ends_with('/')
+                    && let Some(path) = self.load_as_file(&cached_path, tsconfig, ctx)?
+                {
+                    return Ok(Some(path));
+                }
+                // Otherwise just load the directory.
+                // No modern package manager creates `node_modules/X.js`.
                 if self.cache.is_dir(&cached_path, ctx) {
                     if let Some(path) =
                         self.load_browser_field_or_alias(&cached_path, tsconfig, ctx)?
@@ -942,6 +950,7 @@ impl<Fs: FileSystem> ResolverGeneric<Fs> {
                     if let Some(path) = self.load_as_directory(&cached_path, tsconfig, ctx)? {
                         return Ok(Some(path));
                     }
+                // Still need to try to load the file in case there are path aliases.
                 } else if let Some(path) = self.load_as_file(&cached_path, tsconfig, ctx)? {
                     return Ok(Some(path));
                 }

fixtures/enhanced-resolve/test/fixtures/node_modules/@scope/dir-and-file/foo/bar.js

@@ -49,7 +49,11 @@ fn resolve() {
         ("handle fragment edge case (no fragment)", f.clone(), "./no#fragment/#/#", f.join("no#fragment/#/#.js")),
         ("handle fragment edge case (fragment)", f.clone(), "./no#fragment/#/", f.join("no.js#fragment/#/")),
         ("handle fragment escaping", f.clone(), "./no\0#fragment/\0#/\0##fragment", f.join("no#fragment/#/#.js#fragment")),
-
+        // Test `node_modules/X/foo/` and `node_modules/X/foo.js` precedence.
+        ("file and dir precedence 1", f.clone(), "dir-and-file/foo", f.join("node_modules/dir-and-file/foo.js")),
+        ("file and dir precedence 2", f.clone(), "@scope/dir-and-file/foo", f.join("node_modules/@scope/dir-and-file/foo.js")),
+        ("file and dir precedence 1", f.clone(), "dir-and-file/foo/", f.join("node_modules/dir-and-file/foo/index.js")),
+        ("file and dir precedence 2", f.clone(), "@scope/dir-and-file/foo/", f.join("node_modules/@scope/dir-and-file/foo/index.js")),
     ];
 
     for (comment, path, request, expected) in pass {