[wasm] Make FileManager.createFile() work on WASI (#992)

* [wasm] Make `FileManager.createFile()` work on WASI

fixes swiftwasm/swift#5593

`FileManager.createFile()` currently doesn't work on WASI because it
requires `.atomic`, it requires creating a temporary file, and it isn't
suppported on WASI.

So I have fixed that by removing the `.atomic` requirement only on WASI.

* [wasm] Make `Data.WritingOptions.atomic` unavailable on WASI

`writeToFileAux`, `createTemporaryFile`, and `createProtectedTemporaryFile` also become unavailable on WASI.

Author: kkebo

Benchmarks/Benchmarks/DataIO/BenchmarkDataIO.swift

@@ -88,9 +88,11 @@ let benchmarks = {
         try data.write(to: testPath)
     }
 
+#if !os(WASI) // atomic writing is unavailable on WASI
     Benchmark("write-regularFile-atomic", configuration: .cleanupTestPathConfig) { benchmark in
         try data.write(to: testPath, options: .atomic)
     }
+#endif
 
     Benchmark("write-regularFile-alreadyExists",
               configuration: .init(
@@ -103,6 +105,7 @@ let benchmarks = {
         try? data.write(to: testPath)
     }
 
+#if !os(WASI) // atomic writing is unavailable on WASI
     Benchmark("write-regularFile-alreadyExists-atomic",
               configuration: .init(
                 setup: {
@@ -113,6 +116,7 @@ let benchmarks = {
     ) { benchmark in
         try? data.write(to: testPath, options: .atomic)
     }
+#endif
 
     Benchmark("read-regularFile", 
               configuration: .init(

Sources/FoundationEssentials/Data/Data+Writing.swift

@@ -142,6 +142,9 @@ private func cleanupTemporaryDirectory(at inPath: String?) {
 }
 
 /// Caller is responsible for calling `close` on the `Int32` file descriptor.
+#if os(WASI)
+@available(*, unavailable, message: "WASI does not have temporary directories")
+#endif
 private func createTemporaryFile(at destinationPath: String, inPath: PathOrURL, prefix: String, options: Data.WritingOptions, variant: String? = nil) throws -> (Int32, String) {
 #if os(WASI)
     // WASI does not have temp directories
@@ -206,7 +209,14 @@ private func createTemporaryFile(at destinationPath: String, inPath: PathOrURL,
 
 /// Returns `(file descriptor, temporary file path, temporary directory path)`
 /// Caller is responsible for calling `close` on the `Int32` file descriptor and calling `cleanupTemporaryDirectory` on the temporary directory path. The temporary directory path may be nil, if it does not need to be cleaned up.
+#if os(WASI)
+@available(*, unavailable, message: "WASI does not have temporary directories")
+#endif
 private func createProtectedTemporaryFile(at destinationPath: String, inPath: PathOrURL, options: Data.WritingOptions, variant: String? = nil) throws -> (Int32, String, String?) {
+#if os(WASI)
+    // WASI does not have temp directories
+    throw CocoaError(.featureUnsupported)
+#else
 #if FOUNDATION_FRAMEWORK
     if _foundation_sandbox_check(getpid(), nil) != 0 {
         // Convert the path back into a string
@@ -248,6 +258,7 @@ private func createProtectedTemporaryFile(at destinationPath: String, inPath: Pa
     let temporaryDirectoryPath = destinationPath.deletingLastPathComponent()
     let (fd, auxFile) = try createTemporaryFile(at: temporaryDirectoryPath, inPath: inPath, prefix: ".dat.nosync", options: options, variant: variant)
     return (fd, auxFile, nil)
+#endif // os(WASI)
 }
 
 private func write(buffer: UnsafeRawBufferPointer, toFileDescriptor fd: Int32, path: PathOrURL, parentProgress: Progress?) throws {
@@ -322,15 +333,26 @@ internal func writeToFile(path inPath: PathOrURL, data: Data, options: Data.Writ
 }
 
 internal func writeToFile(path inPath: PathOrURL, buffer: UnsafeRawBufferPointer, options: Data.WritingOptions, attributes: [String : Data] = [:], reportProgress: Bool = false) throws {
+#if os(WASI) // `.atomic` is unavailable on WASI
+    try writeToFileNoAux(path: inPath, buffer: buffer, options: options, attributes: attributes, reportProgress: reportProgress)
+#else
     if options.contains(.atomic) {
         try writeToFileAux(path: inPath, buffer: buffer, options: options, attributes: attributes, reportProgress: reportProgress)
     } else {
         try writeToFileNoAux(path: inPath, buffer: buffer, options: options, attributes: attributes, reportProgress: reportProgress)
     }
+#endif
 }
 
 /// Create a new file out of `Data` at a path, using atomic writing.
+#if os(WASI)
+@available(*, unavailable, message: "atomic writing is unavailable in WASI because temporary files are not supported")
+#endif
 private func writeToFileAux(path inPath: PathOrURL, buffer: UnsafeRawBufferPointer, options: Data.WritingOptions, attributes: [String : Data], reportProgress: Bool) throws {
+#if os(WASI)
+    // `.atomic` is unavailable on WASI
+    throw CocoaError(.featureUnsupported)
+#else
     assert(options.contains(.atomic))
 
     // TODO: Somehow avoid copying back and forth to a String to hold the path
@@ -503,7 +525,6 @@ private func writeToFileAux(path inPath: PathOrURL, buffer: UnsafeRawBufferPoint
 
                 cleanupTemporaryDirectory(at: temporaryDirectoryPath)
 
-#if !os(WASI) // WASI does not support fchmod for now
                 if let mode {
                     // Try to change the mode if the path has not changed. Do our best, but don't report an error.
 #if FOUNDATION_FRAMEWORK
@@ -527,16 +548,18 @@ private func writeToFileAux(path inPath: PathOrURL, buffer: UnsafeRawBufferPoint
                     fchmod(fd, mode)
 #endif
                 }
-#endif // os(WASI)
             }
         }
     }
 #endif
+#endif // os(WASI)
 }
 
 /// Create a new file out of `Data` at a path, not using atomic writing.
 private func writeToFileNoAux(path inPath: PathOrURL, buffer: UnsafeRawBufferPointer, options: Data.WritingOptions, attributes: [String : Data], reportProgress: Bool) throws {
+#if !os(WASI) // `.atomic` is unavailable on WASI
     assert(!options.contains(.atomic))
+#endif
 
 #if os(Windows)
     try inPath.path.withNTPathRepresentation { pwszPath in

Sources/FoundationEssentials/Data/Data.swift

@@ -2099,6 +2099,9 @@ public struct Data : Equatable, Hashable, RandomAccessCollection, MutableCollect
         public init(rawValue: UInt) { self.rawValue = rawValue }
 
         /// An option to write data to an auxiliary file first and then replace the original file with the auxiliary file when the write completes.
+#if os(WASI)
+        @available(*, unavailable, message: "atomic writing is unavailable in WASI because temporary files are not supported")
+#endif
         public static let atomic = WritingOptions(rawValue: 1 << 0)
 
         /// An option that attempts to write data to a file and fails with an error if the destination file already exists.
@@ -2474,9 +2477,11 @@ public struct Data : Equatable, Hashable, RandomAccessCollection, MutableCollect
     /// - parameter options: Options for writing the data. Default value is `[]`.
     /// - throws: An error in the Cocoa domain, if there is an error writing to the `URL`.
     public func write(to url: URL, options: Data.WritingOptions = []) throws {
+#if !os(WASI) // `.atomic` is unavailable on WASI
         if options.contains(.withoutOverwriting) && options.contains(.atomic) {
             fatalError("withoutOverwriting is not supported with atomic")
         }
+#endif
 
         guard url.isFileURL else {
             throw CocoaError(.fileWriteUnsupportedScheme)

Sources/FoundationEssentials/FileManager/FileManager+Files.swift

@@ -260,6 +260,9 @@ extension _FileManagerImpl {
             }
             attr?[.protectionKey] = nil
         }
+        #elseif os(WASI)
+        // `.atomic` is unavailable on WASI
+        let opts: Data.WritingOptions = []
         #else
         let opts = Data.WritingOptions.atomic
         #endif

Sources/FoundationEssentials/String/String+IO.swift

@@ -433,7 +433,12 @@ extension StringProtocol {
             attributes = [:]
         }
 
+#if os(WASI)
+        guard !useAuxiliaryFile else { throw CocoaError(.featureUnsupported) }
+        let options : Data.WritingOptions = []
+#else
         let options : Data.WritingOptions = useAuxiliaryFile ? [.atomic] : []
+#endif
 
         try writeToFile(path: .path(String(path)), data: data, options: options, attributes: attributes, reportProgress: false)
     }
@@ -451,7 +456,12 @@ extension StringProtocol {
             attributes = [:]
         }
 
+#if os(WASI)
+        guard !useAuxiliaryFile else { throw CocoaError(.featureUnsupported) }
+        let options : Data.WritingOptions = []
+#else
         let options : Data.WritingOptions = useAuxiliaryFile ? [.atomic] : []
+#endif
 
         try writeToFile(path: .url(url), data: data, options: options, attributes: attributes, reportProgress: false)
     }

Tests/FoundationEssentialsTests/DataIOTests.swift

@@ -93,6 +93,9 @@ class DataIOTests : XCTestCase {
 
     // Atomic writing is a very different code path
     func test_readWriteAtomic() throws {
+        #if os(WASI)
+        try XCTSkip("atomic writing is not supported on WASI")
+        #else
         let url = testURL()
         // Perform an atomic write to a file that does not exist
         try writeAndVerifyTestData(to: url, writeOptions: [.atomic])
@@ -101,6 +104,7 @@ class DataIOTests : XCTestCase {
         try writeAndVerifyTestData(to: url, writeOptions: [.atomic])
 
         cleanup(at: url)
+        #endif
     }
 
     func test_readWriteMapped() throws {