Allow FileSystem.exists to follow symlinks or not

Sources/Basic/FileSystem.swift

@@ -115,7 +115,7 @@ public enum FileMode {
 // FIXME: Design an asynchronous story?
 public protocol FileSystem: class {
     /// Check whether the given path exists and is accessible.
-    func exists(_ path: AbsolutePath) -> Bool
+    func exists(_ path: AbsolutePath, followSymlink: Bool) -> Bool
 
     /// Check whether the given path is accessible and a directory.
     func isDirectory(_ path: AbsolutePath) -> Bool
@@ -168,6 +168,11 @@ public protocol FileSystem: class {
 /// Convenience implementations (default arguments aren't permitted in protocol
 /// methods).
 public extension FileSystem {
+    /// exists override with default value.
+    func exists(_ path: AbsolutePath) -> Bool {
+        return exists(path, followSymlink: true)
+    }
+
     /// Default implementation of createDirectory(_:)
     func createDirectory(_ path: AbsolutePath) throws {
         try createDirectory(path, recursive: false)
@@ -197,8 +202,8 @@ private class LocalFileSystem: FileSystem {
         return filestat.st_mode & libc.S_IXUSR != 0
     }
 
-    func exists(_ path: AbsolutePath) -> Bool {
-        return Basic.exists(path)
+    func exists(_ path: AbsolutePath, followSymlink: Bool) -> Bool {
+        return Basic.exists(path, followSymlink: followSymlink)
     }
 
     func isDirectory(_ path: AbsolutePath) -> Bool {
@@ -332,7 +337,7 @@ private class LocalFileSystem: FileSystem {
     }
 
     func removeFileTree(_ path: AbsolutePath) throws {
-        if self.exists(path) {
+        if self.exists(path, followSymlink: false) {
             try Basic.removeFileTree(path)
         }
     }
@@ -509,7 +514,7 @@ public class InMemoryFileSystem: FileSystem {
 
     // MARK: FileSystem Implementation
 
-    public func exists(_ path: AbsolutePath) -> Bool {
+    public func exists(_ path: AbsolutePath, followSymlink: Bool) -> Bool {
         do {
             return try getNode(path) != nil
         } catch {
@@ -706,8 +711,8 @@ public class RerootedFileSystemView: FileSystem {
 
     // MARK: FileSystem Implementation
 
-    public func exists(_ path: AbsolutePath) -> Bool {
-        return underlyingFileSystem.exists(formUnderlyingPath(path))
+    public func exists(_ path: AbsolutePath, followSymlink: Bool) -> Bool {
+        return underlyingFileSystem.exists(formUnderlyingPath(path), followSymlink: followSymlink)
     }
 
     public func isDirectory(_ path: AbsolutePath) -> Bool {

Sources/Basic/PathShims.swift

@@ -89,7 +89,7 @@ public func makeDirectories(_ path: AbsolutePath) throws {
 }
 
 /// Recursively deletes the file system entity at `path`.  If there is no file system entity at `path`, this function
-/// does nothing (in particular, this is not considered to be an error).
+/// throws an error.
 public func removeFileTree(_ path: AbsolutePath) throws {
     try FileManager.default.removeItem(atPath: path.asString)
 }

Sources/SourceControl/GitRepository.swift

@@ -561,7 +561,7 @@ private class GitFileSystemView: FileSystem {
         return tree
     }
 
-    func exists(_ path: AbsolutePath) -> Bool {
+    func exists(_ path: AbsolutePath, followSymlink: Bool) -> Bool {
         do {
             return try getEntry(path) != nil
         } catch {

Sources/SourceControl/InMemoryGitRepository.swift

@@ -183,8 +183,8 @@ public final class InMemoryGitRepository {
 
 extension InMemoryGitRepository: FileSystem {
 
-    public func exists(_ path: AbsolutePath) -> Bool {
-        return head.fileSystem.exists(path)
+    public func exists(_ path: AbsolutePath, followSymlink: Bool) -> Bool {
+        return head.fileSystem.exists(path, followSymlink: followSymlink)
     }
 
     public func isDirectory(_ path: AbsolutePath) -> Bool {

Tests/BasicTests/FileSystemTests.swift

@@ -71,6 +71,37 @@ class FileSystemTests: XCTestCase {
         XCTAssertTrue(thisDirectoryContents.contains(where: { $0 == AbsolutePath(#file).basename }))
     }
 
+    func testLocalExistsSymlink() throws {
+        mktmpdir { path in
+            let fs = Basic.localFileSystem
+
+            let source = path.appending(component: "source")
+            let target = path.appending(component: "target")
+            try fs.writeFileContents(target, bytes: "source")
+
+            // Source and target exist.
+
+            try createSymlink(source, pointingAt: target)
+            XCTAssertEqual(fs.exists(source), true)
+            XCTAssertEqual(fs.exists(source, followSymlink: true), true)
+            XCTAssertEqual(fs.exists(source, followSymlink: false), true)
+
+            // Source only exists.
+
+            try fs.removeFileTree(target)
+            XCTAssertEqual(fs.exists(source), false)
+            XCTAssertEqual(fs.exists(source, followSymlink: true), false)
+            XCTAssertEqual(fs.exists(source, followSymlink: false), true)
+
+            // None exist.
+
+            try fs.removeFileTree(source)
+            XCTAssertEqual(fs.exists(source), false)
+            XCTAssertEqual(fs.exists(source, followSymlink: true), false)
+            XCTAssertEqual(fs.exists(source, followSymlink: false), false)
+        }
+    }
+
     func testLocalCreateDirectory() throws {
         let fs = Basic.localFileSystem
 
@@ -378,6 +409,7 @@ class FileSystemTests: XCTestCase {
         ("testLocalBasics", testLocalBasics),
         ("testLocalCreateDirectory", testLocalCreateDirectory),
         ("testLocalReadWriteFile", testLocalReadWriteFile),
+        ("testLocalExistsSymlink", testLocalExistsSymlink),
         ("testInMemoryBasics", testInMemoryBasics),
         ("testInMemoryCreateDirectory", testInMemoryCreateDirectory),
         ("testInMemoryFsCopy", testInMemoryFsCopy),