os: Truncate on Windows will not create a new file

Truncating a non existent file currently creates a new blank file. This
behavior is not consistent with other OSes where a file not found error
would instead be returned. This change makes Truncate on Windows return
a file-not-found error when the specified file doesn't exist, bringing
the behavior consistent.

New test cases have been added to prevent a regression.

Fixes 58977

Author: nwnt

src/os/file_windows.go

@@ -160,7 +160,7 @@ func (f *File) seek(offset int64, whence int) (ret int64, err error) {
 // Truncate changes the size of the named file.
 // If the file is a symbolic link, it changes the size of the link's target.
 func Truncate(name string, size int64) error {
-	f, e := OpenFile(name, O_WRONLY|O_CREATE, 0666)
+	f, e := OpenFile(name, O_WRONLY, 0666)
 	if e != nil {
 		return e
 	}

src/os/os_test.go

@@ -1335,6 +1335,33 @@ func TestTruncate(t *testing.T) {
 	}
 }
 
+func TestTruncateNonExistenceFile(t *testing.T) {
+	t.Parallel()
+
+	nonExistenceFileName := "./ThisFileDoesNotExist"
+	err := os.Truncate(nonExistenceFileName, 1)
+	if err == nil {
+		t.Error("Expect an error when truncating a non-existence file")
+	}
+	if !os.IsNotExist(err) {
+		t.Error("The error's Err field is not set properly")
+	}
+
+	pathErr, ok := err.(*os.PathError)
+	if !ok {
+		t.Errorf("Incorrect error type, got %T, want *os.PathError", err)
+	}
+	if pathErr.Path != nonExistenceFileName {
+		t.Errorf("Incorrect error file path, got %s, want %s", pathErr.Path, nonExistenceFileName)
+	}
+
+	// Truncate shouldn't create any new file.
+	if file, err := os.Open(nonExistenceFileName); (file != nil && err == nil) || !os.IsNotExist(err) {
+		file.Close()
+		t.Error("Truncating a non existence file should not create a new file")
+	}
+}
+
 // Use TempDir (via newFile) to make sure we're on a local file system,
 // so that timings are not distorted by latency and caching.
 // On NFS, timings can be off due to caching of meta-data on