Very verbose error message, but still cannot resolve the problem.

mc_work/dorun.go

@@ -11,6 +11,7 @@ import (
 	"math"
 	"math/rand"
 	"os"
+	"path/filepath"
 	"sync"
 
 	"example.com/ackley_mc/ackley"
@@ -68,7 +69,7 @@ func isNotSane(mcPrm *McPrm) error {
 // It is part of the exercise, working around file permissions on windows
 func fExists(name string) bool {
 	var err error
-	if _, err := os.Stat (name); err == nil {
+	if _, err = os.Stat(name); err == nil {
 		return true
 	}
 	if errors.Is(err, fs.ErrNotExist) {
@@ -77,26 +78,34 @@ func fExists (name string) bool {
 	return true
 }
 
-
 // createFix is a wrapper around os.Create() which I seem to need for windows.
 // On windows, I cannot overwrite an existing file. To be very exact, the
 // O_CREATE fails if a file exists. O_TRUNC also fails.
+// Doing an open on the file gives the same, "The system cannot find the file specified"
+// The calls fail, even if the file does not exist. It must be a problem
+// with permissions on the directory, not the file.
 func createFix(name string) (*os.File, error) {
-	var rErr = `Remove the file %s and try again. This only happens on windows: %w`
+	longErr := `%s does not exist, but could not create it.
+Tried setting pemissions on directory %s, but failed:
+%w`
 	var f *os.File
 	var err error
 	if f, err = os.Create(name); err == nil {
 		return f, nil // Most common path (no problem)
 	}
+	if !fExists(name) { // does not exist, but we have a problem.
+		var t string
+		if t, err = filepath.Abs(name); err != nil {
+			return nil, fmt.Errorf("cannot work out path %w", err)
+		}
+		d := filepath.Dir(t)
+		e := os.Chmod(d, 0200)
+		if e != nil {	
+			return nil, fmt.Errorf(longErr, name, d, e)
+		}
 
-	if !fExists(name) { // does not exist, but we have a real error.
-		return nil, err // Return original error
-	} // Next step try to remove original file
-    if e := os.Remove (name); e != nil {
-		return nil, fmt.Errorf (rErr, name, e)
-	}
-	if f, err = os.Create(name); err == nil { // second attempt, after removing name
-		return f, nil
+	} else { // the file exists
+		fmt.Println("file exists, what to do ?")
 	}
 	return nil, err
 }