First pass at fixing issue 99

A lot of code touched because low level functions needed to pass up
error messages reliably, and this had to propagate up the entire
driver hierarchy.

Tested OK *in English* on:
     > Linux
     > OSX 10.10.x
     > Windows VS2017
     > Windows mingw64
I have no way to test on Android, but it might work.

TODO: Needs testing in other languages to verify proper UTF8 error messages,
      esp. with Windows VS, due to complexities with FormatMessage() -- see get_ms_errmsg()

8 files changed, 63 insertions, 19 deletions

diff --git a/src/drivers/Android/Fl_Android_System_Driver.H b/src/drivers/Android/Fl_Android_System_Driver.H
index 2a8682ddb..198d7a2b3 100644
--- a/src/drivers/Android/Fl_Android_System_Driver.H
+++ b/src/drivers/Android/Fl_Android_System_Driver.H
@@ -70,7 +70,9 @@ public:
   // these 2 are in Fl_get_key_win32.cxx
   virtual int event_key(int k);
   virtual int get_key(int k);
-  virtual int filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) );
+  virtual int filename_list(const char *d, dirent ***list,
+                            int (*sort)(struct dirent **, struct dirent **),
+                            char *errmsg, int errmsg_sz);
   virtual int filename_expand(char *to,int tolen, const char *from);
   virtual int filename_relative(char *to, int tolen, const char *from, const char *base);
   virtual int filename_absolute(char *to, int tolen, const char *from);
@@ -80,7 +82,9 @@ public:
   virtual int open_uri(const char *uri, char *msg, int msglen);
   virtual int use_recent_tooltip_fix() {return 1;}
   virtual int file_browser_load_filesystem(Fl_File_Browser *browser, char *filename, int lname, Fl_File_Icon *icon);
-  virtual int file_browser_load_directory(const char *directory, char *filename, size_t name_size, dirent ***pfiles, Fl_File_Sort_F *sort);
+  virtual int file_browser_load_directory(const char *directory, char *filename, size_t name_size,
+                                          dirent ***pfiles, Fl_File_Sort_F *sort,
+                                          char *errmsg=NULL, int errmsg_sz=0);
   virtual void newUUID(char *uuidBuffer);
   virtual char *preference_rootnode(Fl_Preferences *prefs, Fl_Preferences::Root root, const char *vendor,
                                     const char *application);
diff --git a/src/drivers/Android/Fl_Android_System_Driver.cxx b/src/drivers/Android/Fl_Android_System_Driver.cxx
index e6aa970e4..0fa9671c5 100644
--- a/src/drivers/Android/Fl_Android_System_Driver.cxx
+++ b/src/drivers/Android/Fl_Android_System_Driver.cxx
@@ -486,11 +486,13 @@ int Fl_WinAPI_System_Driver::clocale_printf(FILE *output, const char *format, va
   return retval;
 }
 
-int Fl_WinAPI_System_Driver::filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) ) {
+int Fl_WinAPI_System_Driver::filename_list(const char *d, dirent ***list,
+                                           int (*sort)(struct dirent **, struct dirent **),
+                                           char *errmsg, int errmsg_sz ) {
   // For Windows we have a special scandir implementation that uses
   // the Win32 "wide" functions for lookup, avoiding the code page mess
   // entirely. It also fixes up the trailing '/'.
-  return fl_scandir(d, list, 0, sort);
+  return fl_scandir(d, list, 0, sort, errmsg, errmsg_sz);
 }
 
 int Fl_WinAPI_System_Driver::filename_expand(char *to, int tolen, const char *from) {
@@ -747,7 +749,9 @@ int Fl_WinAPI_System_Driver::file_browser_load_filesystem(Fl_File_Browser *brows
 }
 
 int Fl_WinAPI_System_Driver::file_browser_load_directory(const char *directory, char *filename,
-                                                         size_t name_size, dirent ***pfiles, Fl_File_Sort_F *sort)
+                                                         size_t name_size, dirent ***pfiles,
+                                                         Fl_File_Sort_F *sort,
+                                                         char *errmsg, int errmsg_sz)
 {
   strlcpy(filename, directory, name_size);
   int i = (int) (strlen(filename) - 1);
@@ -756,7 +760,7 @@ int Fl_WinAPI_System_Driver::file_browser_load_directory(const char *directory,
     filename[2] = '/';
   else if (filename[i] != '/' && filename[i] != '\\')
     strlcat(filename, "/", name_size);
-  return filename_list(filename, pfiles, sort);
+  return filename_list(filename, pfiles, sort, errmsg, errmsg_sz);
 }
 
 void Fl_WinAPI_System_Driver::newUUID(char *uuidBuffer)
diff --git a/src/drivers/Darwin/Fl_Darwin_System_Driver.H b/src/drivers/Darwin/Fl_Darwin_System_Driver.H
index ee7ab30ea..548277901 100644
--- a/src/drivers/Darwin/Fl_Darwin_System_Driver.H
+++ b/src/drivers/Darwin/Fl_Darwin_System_Driver.H
@@ -52,7 +52,9 @@ public:
   // these 2 are in Fl_get_key_mac.cxx
   virtual int event_key(int k);
   virtual int get_key(int k);
-  virtual int filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) );
+  virtual int filename_list(const char *d, dirent ***list,
+                            int (*sort)(struct dirent **, struct dirent **),
+                            char *errmsg=NULL, int errmsg_sz=0);
   virtual int open_uri(const char *uri, char *msg, int msglen);
   virtual int need_test_shortcut_extra() {return 1;}
   virtual int file_browser_load_filesystem(Fl_File_Browser *browser, char *filename, int lname, Fl_File_Icon *icon);
diff --git a/src/drivers/Darwin/Fl_Darwin_System_Driver.cxx b/src/drivers/Darwin/Fl_Darwin_System_Driver.cxx
index 51a416b87..0c1a9de9e 100644
--- a/src/drivers/Darwin/Fl_Darwin_System_Driver.cxx
+++ b/src/drivers/Darwin/Fl_Darwin_System_Driver.cxx
@@ -15,6 +15,7 @@
 //
 
 #include "Fl_Darwin_System_Driver.H"
+#include <src/flstring.h>
 #include <FL/platform.H>
 #include <FL/Fl.H>
 #include <FL/Fl_File_Browser.H>
@@ -139,7 +140,9 @@ void *Fl_Darwin_System_Driver::get_carbon_function(const char *function_name) {
   return (carbon ? dlsym(carbon, function_name) : NULL);
 }
 
-int Fl_Darwin_System_Driver::filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) ) {
+int Fl_Darwin_System_Driver::filename_list(const char *d, dirent ***list,
+                                           int (*sort)(struct dirent **, struct dirent **),
+                                           char *errmsg, int errmsg_sz) {
   int dirlen;
   char *dirloc;
   // Assume that locale encoding is no less dense than UTF-8
@@ -150,6 +153,10 @@ int Fl_Darwin_System_Driver::filename_list(const char *d, dirent ***list, int (*
 # else
   int n = scandir(dirloc, list, 0, (int(*)(const void*,const void*))sort);
 # endif
+  if (n==-1) {
+    if (errmsg) fl_snprintf(errmsg, errmsg_sz, "%s", strerror(errno));
+    return -1;
+  }
   // convert every filename to UTF-8, and append a '/' to all
   // filenames that are directories
   int i;
diff --git a/src/drivers/WinAPI/Fl_WinAPI_System_Driver.H b/src/drivers/WinAPI/Fl_WinAPI_System_Driver.H
index e6446923d..91b230d5f 100644
--- a/src/drivers/WinAPI/Fl_WinAPI_System_Driver.H
+++ b/src/drivers/WinAPI/Fl_WinAPI_System_Driver.H
@@ -68,7 +68,9 @@ public:
   // these 2 are in Fl_get_key_win32.cxx
   virtual int event_key(int k);
   virtual int get_key(int k);
-  virtual int filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) );
+  virtual int filename_list(const char *d, dirent ***list,
+                            int (*sort)(struct dirent **, struct dirent **),
+                            char *errmsg=NULL, int errmsg_sz=0);
   virtual int filename_expand(char *to,int tolen, const char *from);
   virtual int filename_relative(char *to, int tolen, const char *from, const char *base);
   virtual int filename_absolute(char *to, int tolen, const char *from);
@@ -78,7 +80,9 @@ public:
   virtual int open_uri(const char *uri, char *msg, int msglen);
   virtual int use_recent_tooltip_fix() {return 1;}
   virtual int file_browser_load_filesystem(Fl_File_Browser *browser, char *filename, int lname, Fl_File_Icon *icon);
-  virtual int file_browser_load_directory(const char *directory, char *filename, size_t name_size, dirent ***pfiles, Fl_File_Sort_F *sort);
+  virtual int file_browser_load_directory(const char *directory, char *filename, size_t name_size,
+                                          dirent ***pfiles, Fl_File_Sort_F *sort,
+                                          char *errmsg=NULL, int errmsg_sz=0);
   virtual void newUUID(char *uuidBuffer);
   virtual char *preference_rootnode(Fl_Preferences *prefs, Fl_Preferences::Root root, const char *vendor,
                                     const char *application);
diff --git a/src/drivers/WinAPI/Fl_WinAPI_System_Driver.cxx b/src/drivers/WinAPI/Fl_WinAPI_System_Driver.cxx
index ab20cfe32..592e192e3 100644
--- a/src/drivers/WinAPI/Fl_WinAPI_System_Driver.cxx
+++ b/src/drivers/WinAPI/Fl_WinAPI_System_Driver.cxx
@@ -61,7 +61,8 @@ static wchar_t *wbuf1 = NULL;
 extern "C" {
   int fl_scandir(const char *dirname, struct dirent ***namelist,
                  int (*select)(struct dirent *),
-                 int (*compar)(struct dirent **, struct dirent **));
+                 int (*compar)(struct dirent **, struct dirent **),
+                 char *errmsg, int errmsg_len);
 }
 
 /*
@@ -488,11 +489,13 @@ int Fl_WinAPI_System_Driver::clocale_printf(FILE *output, const char *format, va
   return retval;
 }
 
-int Fl_WinAPI_System_Driver::filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) ) {
+int Fl_WinAPI_System_Driver::filename_list(const char *d, dirent ***list,
+                                           int (*sort)(struct dirent **, struct dirent **),
+                                           char *errmsg, int errmsg_sz) {
   // For Windows we have a special scandir implementation that uses
   // the Win32 "wide" functions for lookup, avoiding the code page mess
   // entirely. It also fixes up the trailing '/'.
-  return fl_scandir(d, list, 0, sort);
+  return fl_scandir(d, list, 0, sort, errmsg, errmsg_sz);
 }
 
 int Fl_WinAPI_System_Driver::filename_expand(char *to, int tolen, const char *from) {
@@ -749,7 +752,9 @@ int Fl_WinAPI_System_Driver::file_browser_load_filesystem(Fl_File_Browser *brows
 }
 
 int Fl_WinAPI_System_Driver::file_browser_load_directory(const char *directory, char *filename,
-                                                         size_t name_size, dirent ***pfiles, Fl_File_Sort_F *sort)
+                                                         size_t name_size, dirent ***pfiles,
+                                                         Fl_File_Sort_F *sort,
+                                                         char *errmsg, int errmsg_sz)
 {
   strlcpy(filename, directory, name_size);
   int i = (int) (strlen(filename) - 1);
@@ -758,7 +763,7 @@ int Fl_WinAPI_System_Driver::file_browser_load_directory(const char *directory,
     filename[2] = '/';
   else if (filename[i] != '/' && filename[i] != '\\')
     strlcat(filename, "/", name_size);
-  return filename_list(filename, pfiles, sort);
+  return filename_list(filename, pfiles, sort, errmsg, errmsg_sz);
 }
 
 void Fl_WinAPI_System_Driver::newUUID(char *uuidBuffer)
diff --git a/src/drivers/X11/Fl_X11_System_Driver.H b/src/drivers/X11/Fl_X11_System_Driver.H
index 7c2306a28..f8fddc741 100644
--- a/src/drivers/X11/Fl_X11_System_Driver.H
+++ b/src/drivers/X11/Fl_X11_System_Driver.H
@@ -34,7 +34,9 @@ public:
   // these 2 are in Fl_get_key.cxx
   virtual int event_key(int k);
   virtual int get_key(int k);
-  virtual int filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) );
+  virtual int filename_list(const char *d, dirent ***list,
+                            int (*sort)(struct dirent **, struct dirent **),
+                            char *errmsg=NULL, int errmsg_sz=0);
   virtual int need_menu_handle_part1_extra() {return 1;}
   virtual int open_uri(const char *uri, char *msg, int msglen);
   virtual int use_tooltip_timeout_condition() {return 1;}
diff --git a/src/drivers/X11/Fl_X11_System_Driver.cxx b/src/drivers/X11/Fl_X11_System_Driver.cxx
index 0714ff753..28827bcfc 100644
--- a/src/drivers/X11/Fl_X11_System_Driver.cxx
+++ b/src/drivers/X11/Fl_X11_System_Driver.cxx
@@ -25,7 +25,8 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <pwd.h>
-
+#include <string.h>     // strerror(errno)
+#include <errno.h>      // errno
 
 #if defined(_AIX)
 extern "C" {
@@ -56,7 +57,8 @@ extern "C" {
 extern "C" {
   int fl_scandir(const char *dirname, struct dirent ***namelist,
                  int (*select)(struct dirent *),
-                 int (*compar)(struct dirent **, struct dirent **));
+                 int (*compar)(struct dirent **, struct dirent **),
+                 char *errmsg, int errmsg_sz);
 }
 #endif
 
@@ -444,10 +446,19 @@ int Fl_X11_System_Driver::XParseGeometry(const char* string, int* x, int* y,
   return ::XParseGeometry(string, x, y, width, height);
 }
 
-int Fl_X11_System_Driver::filename_list(const char *d, dirent ***list, int (*sort)(struct dirent **, struct dirent **) ) {
+//
+// Needs some docs
+// Returns -1 on error, errmsg will contain OS error if non-NULL.
+//
+int Fl_X11_System_Driver::filename_list(const char *d,
+                                        dirent ***list,
+                                        int (*sort)(struct dirent **, struct dirent **),
+                                        char *errmsg, int errmsg_sz) {
   int dirlen;
   char *dirloc;
 
+  if (errmsg && errmsg_sz>0) errmsg[0] = '\0';
+
   // Assume that locale encoding is no less dense than UTF-8
   dirlen = strlen(d);
   dirloc = (char *)malloc(dirlen + 1);
@@ -476,6 +487,11 @@ int Fl_X11_System_Driver::filename_list(const char *d, dirent ***list, int (*sor
 
   free(dirloc);
 
+  if (n==-1) {
+    if (errmsg) fl_snprintf(errmsg, errmsg_sz, "%s", strerror(errno));
+    return -1;
+  }
+
   // convert every filename to UTF-8, and append a '/' to all
   // filenames that are directories
   int i;