I think I have a reasonable solution to your problem in version 2.15.  I'm simply calling it "Improved Save Location."  It exhibits slightly different  (and more desirable, I think) initial directories for saving files.

First, any file that will be saved  via "Save As..." will initially attempt to use its previous directory as the save point if you're attempting to save an existing file under a new name.  I think everyone will agree that this behavior probably should have always been present.

Second, if we're saving a new file and other tabs are open, it will default to the directory of the most recently opened or saved editor tab that is currently open.  If no other tabs are open, though, it will default to the project directory.  This behavior deviates significantly from Windows's defaults, but it is pretty common in many editors.

I think these changes should solve your problem without creating a misleading "Source Directory" setting.  I'm mildly against that concept due to confusion that could arise at users thinking it is the only source directory.

Let me know what you think!

I know you've had issues with path handling in regards to file saving locations with Simply Fortran.  I'm concerned, though, that your proposal  (in this case, at least) is a bit too general and possibly misleading.  Saying simply "Source Files Directory" implies that it's the only location for source files.  Additionally, that tab might not be the best place to indicate such a directory because those locations now specified are locations needed by the compiler (although the tab's name does not imply this).

Right now Simply Fortran should be using Windows' default "Save As..." directory behavior.  I'm not saying that the default is ideal or even desirable, but it is at least consistent with other software.

I'll try to think of a more general way to set such a directory.  It would probably be stored in either the File menu or Option menu, but it probably wouldn't be in the Project Options window.  I just want to avoid its appearance of influencing anything beyond the "Save As..." menu option.

OPTIONS
  > Project
      > File locations tab
           > Source files directory   [ NEW OPTION ]
           > Build directory
           > Modules directory

Purpose:
Set an optional default for source file opening/saving/saving-as.

Funtionality:
If left blank, functionality left unchanged as-now.
If set, saves to the stated directory unless over-ridden manually with a save-as,
and points all file open/save/save-as dialogs initially at the stated directory.

Why needed:
Windows doesn't always guess correctly where we want to save stuff.
Example: when source files are stored along a different branch of the file structure from project and object files.
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John