Make `FileSystem.isLink` actually work (#214)

* Make `FileSystem.isLink` actually work

`FileSystem.isLink` called `FileSystem.type` with the default
argument of `followLinks: true`.  This is obviously wrong since it
would mean that `isLink` would never return true (except maybe for
broken symbolic links).

Make `FileSystem.isLink` use `followLinks: false`.  This is what
`dart:io`'s `FileSystemEntity.isLink` is documented to do.

Partially addresses https://github.com/google/file.dart/issues/8.

* Reorganize isFile/isDirectory/isLink tests

Reorganize the isFile/isDirectory/isLink tests so that the test names
are more appropriate.

packages/file/CHANGELOG.md

diff --git a/packages/file/CHANGELOG.md b/packages/file/CHANGELOG.md
index e067af9..dd09a11 100644
--- a/packages/file/CHANGELOG.md
+++ b/packages/file/CHANGELOG.md
@@ -1,6 +1,7 @@
 #### 7.0.0-wip
 
 * Dart 3 fixes for class modifiers.
+* Fix `FileSystem.isLink`/`FileSystem.isLinkSync` to not follow symbolic links.
 
 #### 6.1.4
 

packages/file/lib/src/interface/file_system.dart

diff --git a/packages/file/lib/src/interface/file_system.dart b/packages/file/lib/src/interface/file_system.dart
index da898a3..4fd528d 100644
--- a/packages/file/lib/src/interface/file_system.dart
+++ b/packages/file/lib/src/interface/file_system.dart
@@ -138,12 +138,12 @@
 
   /// Checks if [`type(path)`](type) returns [io.FileSystemEntityType.LINK].
   Future<bool> isLink(String path) async =>
-      await type(path) == io.FileSystemEntityType.link;
+      await type(path, followLinks: false) == io.FileSystemEntityType.link;
 
   /// Synchronously checks if [`type(path)`](type) returns
   /// [io.FileSystemEntityType.LINK].
   bool isLinkSync(String path) =>
-      typeSync(path) == io.FileSystemEntityType.link;
+      typeSync(path, followLinks: false) == io.FileSystemEntityType.link;
 
   /// Gets the string path represented by the specified generic [path].
   ///

packages/file/test/common_tests.dart

diff --git a/packages/file/test/common_tests.dart b/packages/file/test/common_tests.dart
index 14010bd..679a90a 100644
--- a/packages/file/test/common_tests.dart
+++ b/packages/file/test/common_tests.dart
@@ -498,6 +498,46 @@
           expect(type, FileSystemEntityType.notFound);
         });
       });
+
+      group('isFile/isDirectory/isLink', () {
+        late String filePath;
+        late String directoryPath;
+        late String fileLinkPath;
+        late String directoryLinkPath;
+
+        setUp(() {
+          filePath = ns('/file');
+          directoryPath = ns('/directory');
+          fileLinkPath = ns('/file-link');
+          directoryLinkPath = ns('/directory-link');
+
+          fs.file(filePath).createSync();
+          fs.directory(directoryPath).createSync();
+          fs.link(fileLinkPath).createSync(filePath);
+          fs.link(directoryLinkPath).createSync(directoryPath);
+        });
+
+        test('isFile', () {
+          expect(fs.isFileSync(filePath), true);
+          expect(fs.isFileSync(directoryPath), false);
+          expect(fs.isFileSync(fileLinkPath), true);
+          expect(fs.isFileSync(directoryLinkPath), false);
+        });
+
+        test('isDirectory', () {
+          expect(fs.isDirectorySync(filePath), false);
+          expect(fs.isDirectorySync(directoryPath), true);
+          expect(fs.isDirectorySync(fileLinkPath), false);
+          expect(fs.isDirectorySync(directoryLinkPath), true);
+        });
+
+        test('isLink', () {
+          expect(fs.isLinkSync(filePath), false);
+          expect(fs.isLinkSync(directoryPath), false);
+          expect(fs.isLinkSync(fileLinkPath), true);
+          expect(fs.isLinkSync(directoryLinkPath), true);
+        });
+      });
     });
 
     group('Directory', () {