add support for the exports package.json attribute

.editorconfig

@@ -17,7 +17,7 @@ block_comment_end = */
 [*.yml]
 indent_size = 1
 
-[package.json]
+[{package.json,.gitmodules}]
 indent_style = tab
 
 [CHANGELOG.md]
@@ -27,7 +27,7 @@ indent_size = 2
 [{*.json,Makefile}]
 max_line_length = off
 
-[test/{dotdot,resolver,module_dir,multirepo,node_path,pathfilter,precedence}/**/*]
+[test/{dotdot,exports,list-exports,resolver,module_dir,multirepo,node_path,pathfilter,precedence}/**/*]
 indent_style = off
 indent_size = off
 max_line_length = off

.eslintignore

@@ -1 +1,2 @@
 node_modules
+test/list-exports/

.eslintrc

@@ -27,6 +27,7 @@
         "object-curly-newline": 0,
         "operator-linebreak": [2, "before"],
         "sort-keys": 0,
+        "eqeqeq": [2, "always", {"null": "ignore"}]
     },
     "overrides": [
         {

.gitignore

@@ -9,3 +9,6 @@ yarn.lock
 
 # symlinked file used in tests
 test/resolver/symlinked/_/node_modules/package
+
+# submodule
+test/list-exports

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "test/list-exports"]
+	path = test/list-exports
+	url = https://github.com/ljharb/list-exports.git
+	branch = main

lib/async.js

@@ -1,9 +1,11 @@
+/* eslint-disable max-lines */
 var fs = require('fs');
 var path = require('path');
 var caller = require('./caller');
 var nodeModulesPaths = require('./node-modules-paths');
 var normalizeOptions = require('./normalize-options');
 var isCore = require('is-core-module');
+var resolveExports = require('./resolve-imports-exports');
 
 var realpathFS = fs.realpath && typeof fs.realpath.native === 'function' ? fs.realpath.native : fs.realpath;
 
@@ -77,6 +79,12 @@ module.exports = function resolve(x, options, callback) {
     var basedir = opts.basedir || path.dirname(caller());
     var parent = opts.filename || basedir;
 
+    if (opts.exportsField == null) {
+        opts.exportsField = { level: 'ignore' };
+    } else if (typeof opts.exportsField === 'string') {
+        opts.exportsField = { level: opts.exportsField };
+    }
+
     opts.paths = opts.paths || [];
 
     // ensure that `basedir` is an absolute path at this point, resolving against the process' current working directory
@@ -265,35 +273,112 @@ module.exports = function resolve(x, options, callback) {
         });
     }
 
-    function processDirs(cb, dirs) {
+    function loadManifestInDir(dir, cb) {
+        maybeRealpath(realpath, dir, opts, function (err, pkgdir) {
+            if (err) return cb(null);
+
+            var pkgfile = path.join(pkgdir, 'package.json');
+            isFile(pkgfile, function (err, ex) {
+                // on err, ex is false
+                if (!ex) return cb(null);
+
+                readFile(pkgfile, function (err, body) {
+                    if (err) cb(err);
+                    try { var pkg = JSON.parse(body); } catch (jsonErr) {}
+
+                    if (pkg && opts.packageFilter) {
+                        pkg = opts.packageFilter(pkg, pkgfile, dir);
+                    }
+                    cb(pkg);
+                });
+            });
+        });
+    }
+
+    function processDirs(cb, dirs, subpath) {
         if (dirs.length === 0) return cb(null, undefined);
         var dir = dirs[0];
 
-        isDirectory(path.dirname(dir), isdir);
-
-        function isdir(err, isdir) {
-            if (err) return cb(err);
-            if (!isdir) return processDirs(cb, dirs.slice(1));
-            loadAsFile(dir, opts.package, onfile);
+        if (opts.exportsField.level !== 'ignore' && endsWithSubpath(dir, subpath)) {
+            var pkgDir = dir.slice(0, dir.length - subpath.length);
+            loadManifestInDir(pkgDir, onmanifestWithExports);
+        } else {
+            onmanifest(false);
         }
 
-        function onfile(err, m, pkg) {
-            if (err) return cb(err);
-            if (m) return cb(null, m, pkg);
-            loadAsDirectory(dir, opts.package, ondir);
+        function onmanifestWithExports(pkg) {
+            if (!pkg || pkg.exports == null) {
+                return onmanifest(false);
+            }
+
+            var resolvedExport;
+            try {
+                resolvedExport = resolveExports(opts.exportsField, pkgDir, parent, subpath, pkg.exports);
+            } catch (resolveErr) {
+                return cb(resolveErr);
+            }
+
+            if (resolvedExport.exact) {
+                isFile(resolvedExport.resolved, function (err, ex) {
+                    if (ex) {
+                        cb(null, resolvedExport.resolved, pkg);
+                    } else {
+                        cb(null, undefined);
+                    }
+                });
+            } else {
+                dir = resolvedExport.resolved;
+                onmanifest(true);
+            }
         }
 
-        function ondir(err, n, pkg) {
-            if (err) return cb(err);
-            if (n) return cb(null, n, pkg);
-            processDirs(cb, dirs.slice(1));
+        function onmanifest(stop) {
+            isDirectory(path.dirname(dir), isdir);
+
+            function isdir(err, isdir) {
+                if (err) return cb(err);
+                if (!isdir) return next();
+                loadAsFile(dir, opts.package, onfile);
+            }
+
+            function onfile(err, m, pkg) {
+                if (err) return cb(err);
+                if (m) return cb(null, m, pkg);
+                loadAsDirectory(dir, opts.package, ondir);
+            }
+
+            function ondir(err, n, pkg) {
+                if (err) return cb(err);
+                if (n) return cb(null, n, pkg);
+                next();
+            }
+
+            function next() {
+                if (stop) {
+                    cb(null, undefined);
+                } else {
+                    processDirs(cb, dirs.slice(1), subpath);
+                }
+            }
         }
     }
+
     function loadNodeModules(x, start, cb) {
+        var subpathIndex = x.charAt(0) === '@' ? x.indexOf('/', x.indexOf('/') + 1) : x.indexOf('/');
+        var subpath = subpathIndex === -1 ? '' : x.slice(subpathIndex);
+
         var thunk = function () { return getPackageCandidates(x, start, opts); };
+
         processDirs(
             cb,
-            packageIterator ? packageIterator(x, start, thunk, opts) : thunk()
+            packageIterator ? packageIterator(x, start, thunk, opts) : thunk(),
+            subpath
         );
     }
+
+    function endsWithSubpath(dir, subpath) {
+        var endOfDir = dir.slice(dir.length - subpath.length);
+
+        return endOfDir === subpath || endOfDir.replace(/\\/g, '/') === subpath;
+    }
 };