Merge branch 'windows_expt' into devel

README.md

@@ -38,6 +38,12 @@ The real documentation is in `go doc` format.
 This is in csv format. For gnuplot, do not forget to `set datafile separator ','`.
 
 # BUGS
+## Real Bugs
+
+Only under windows: I use os.Create() to open a file for writing. In my "Documents" folder, the function call returns "The system cannot find the file specified". Note, this is when creating a file, not opening an existing one. I do not have any error when I run the program from a different directory. I did experiment with chmod() on the directory, but this (a) did not do anything and (b) only the bits set by 0200 are actually affected according to go's documentation. 
+
+## Non bugs
+
 The UI toolkit is "fyne". It does not do charts, so we use go-chart which makes a png, which we can store in memory and feed to the fyne toolkit. Unfortunately, an svg file from go-chart causes fyne to choke. This means we are stuck with png. One day, one should try out the charting library which is based on fyne.
 
 The graphical interface follows no known style convention and looks like it was designed by a three-year old.

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) {
@@ -77,28 +78,32 @@ 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.
+// On windows, this fails if I am in my "Documents" directory.
 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:
+%w
+Please run the program from somewhere other than %s`
+	existErr := `File exists, but unable to write to it:
+%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 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 !fExists(name) { // does not exist, but we have a problem.
+		var d string
+		if t, e := filepath.Abs(name); e != nil {
+			return nil, fmt.Errorf("cannot work out path %w", e)
+		} else {
+			d = filepath.Dir(t)
+		}
+		if _, e := os.Stat(d); e != nil {
+			return nil, fmt.Errorf("parent directory %s is broken %w", d, err)
 		}
-	if f, err = os.Create(name); err == nil { // second attempt, after removing name
-		return f, nil
+		return nil, fmt.Errorf(longErr, name, err, d)
 	}
-	return nil, err
+	return nil, fmt.Errorf(existErr, err) // The file exists..
 }
 
 // setupRun does things like get the cooling rate, seed the random numbers.