Don't use the glob mechanism to parse pre-glob workspace entries (#4711)

lib/src/package.dart

diff --git a/lib/src/package.dart b/lib/src/package.dart
index 88658d6..6dc6711 100644
--- a/lib/src/package.dart
+++ b/lib/src/package.dart
@@ -178,37 +178,46 @@
 
     final workspacePackages =
         pubspec.workspace.expand((workspacePath) {
-          final Glob glob;
-          try {
-            glob = Glob(
-              pubspec.languageVersion.supportsWorkspaceGlobs
-                  ? workspacePath
-                  : Glob.quote(workspacePath),
-            );
-          } on FormatException catch (e) {
-            fail('Failed to parse glob `$workspacePath`. $e');
-          }
           final packages = <Package>[];
-          for (final globResult in glob.listSync(root: dir)) {
-            final pubspecPath = p.join(globResult.path, 'pubspec.yaml');
-            if (!fileExists(pubspecPath)) continue;
-            packages.add(
-              Package.load(
-                globResult.path,
-                loadPubspec: loadPubspec,
-                withPubspecOverrides: withPubspecOverrides,
-              ),
-            );
-          }
-          if (packages.isEmpty) {
-            final globHint =
-                !pubspec.languageVersion.supportsWorkspaceGlobs &&
-                        _looksLikeGlob(workspacePath)
-                    ? '''
+          var globHint = '';
+          if (pubspec.languageVersion.supportsWorkspaceGlobs) {
+            final Glob glob;
+            try {
+              glob = Glob(workspacePath);
+            } on FormatException catch (e) {
+              fail('Failed to parse glob `$workspacePath`. $e');
+            }
+            for (final globResult in glob.listSync(root: dir)) {
+              final pubspecPath = p.join(globResult.path, 'pubspec.yaml');
+              if (!fileExists(pubspecPath)) continue;
+              packages.add(
+                Package.load(
+                  globResult.path,
+                  loadPubspec: loadPubspec,
+                  withPubspecOverrides: withPubspecOverrides,
+                ),
+              );
+            }
+          } else {
+            final pubspecPath = p.join(dir, workspacePath, 'pubspec.yaml');
+            if (!fileExists(pubspecPath)) {
+              if (_looksLikeGlob(workspacePath)) {
+                globHint = '''
 \n\nGlob syntax is only supported from language version ${LanguageVersion.firstVersionWithWorkspaceGlobs}.
 Consider changing the language version of ${p.join(dir, 'pubspec.yaml')} to ${LanguageVersion.firstVersionWithWorkspaceGlobs}.
-'''
-                    : '';
+''';
+              }
+            } else {
+              packages.add(
+                Package.load(
+                  p.join(dir, _useBackSlashesOnWindows(workspacePath)),
+                  loadPubspec: loadPubspec,
+                  withPubspecOverrides: withPubspecOverrides,
+                ),
+              );
+            }
+          }
+          if (packages.isEmpty) {
             fail('''
 No workspace packages matching `$workspacePath`.
 That was included in the workspace of `${p.join(dir, 'pubspec.yaml')}`.$globHint
@@ -574,3 +583,9 @@
 }
 
 bool _looksLikeGlob(String s) => Glob.quote(s) != s;
+String _useBackSlashesOnWindows(String path) {
+  if (Platform.isWindows) {
+    return p.joinAll(p.split(path));
+  }
+  return path;
+}

test/workspace_test.dart

diff --git a/test/workspace_test.dart b/test/workspace_test.dart
index fd060c0..2d33bf3 100644
--- a/test/workspace_test.dart
+++ b/test/workspace_test.dart
@@ -1892,6 +1892,29 @@
     skip: Platform.isWindows, // Cannot create directory named "*" on Windows.
   );
 
+  test('preglob workspace entries can use the platform separator', () async {
+    await dir(appPath, [
+      libPubspec(
+        'myapp',
+        '1.2.3',
+        extras: {
+          'workspace': [p.join('pkgs', 'foo')],
+        },
+        sdk: '^3.6.0',
+      ),
+      dir('pkgs', [
+        dir('foo', [libPubspec('foo', '1.1.1', resolutionWorkspace: true)]),
+      ]),
+    ]).create();
+    await pubGet(environment: {'_PUB_TEST_SDK_VERSION': '3.11.0'});
+    await dir(appPath, [
+      packageConfigFile([
+        packageConfigEntry(name: 'myapp', path: '.'),
+        packageConfigEntry(name: 'foo', path: 'pkgs/foo'),
+      ], generatorVersion: '3.11.0'),
+    ]).validate();
+  });
+
   test('globs are resolved with newer language versions', () async {
     await dir(appPath, [
       libPubspec(