xaccAccountTypes was backwards

vs. the documentation. The unit tests and dialog-account were similarly
backwards, but the use in gnucash/import-export/ofx followed the docs.

gnucash/gnome-utils/dialog-account.c

@@ -589,7 +589,7 @@ make_children_compatible (AccountWindow *aw)
     account = aw_get_account (aw);
     g_return_if_fail (account);
 
-    if (xaccAccountTypesCompatible (xaccAccountGetType (account), aw->type))
+    if (xaccAccountTypesCompatible (aw->type, xaccAccountGetType (account)))
         return;
 
     set_children_types (account, aw->type);
@@ -709,7 +709,7 @@ verify_children_compatible (AccountWindow *aw)
     if (!account)
         return FALSE;
 
-    if (xaccAccountTypesCompatible (xaccAccountGetType (account), aw->type))
+    if (xaccAccountTypesCompatible (aw->type, xaccAccountGetType (account)))
         return TRUE;
 
     if (gnc_account_n_children(account) == 0)

libgnucash/engine/Account.cpp

@@ -4509,8 +4509,17 @@ gboolean
 xaccAccountTypesCompatible (GNCAccountType parent_type,
                             GNCAccountType child_type)
 {
-    return ((xaccParentAccountTypesCompatibleWith (parent_type) &
-             (1 << child_type))
+    /* ACCT_TYPE_NONE isn't compatible with anything, even ACCT_TYPE_NONE. */
+    if (parent_type == ACCT_TYPE_NONE || child_type == ACCT_TYPE_NONE)
+        return FALSE;
+
+    /* ACCT_TYPE_ROOT can't have a parent account, and asking will raise
+     * an error. */
+    if (child_type == ACCT_TYPE_ROOT)
+        return FALSE;
+
+    return ((xaccParentAccountTypesCompatibleWith (child_type) &
+             (1 << parent_type))
             != 0);
 }
 

libgnucash/engine/test/utest-Account.cpp

@@ -2251,9 +2251,8 @@ test_xaccAccountType_Compatibility (void)
     auto check2 = test_error_struct_new(logdomain, loglevel, msg2);
     gint loghandler;
 
-    for (type = ACCT_TYPE_BANK; type < NUM_ACCOUNT_TYPES; type = ++type)
+    for (type = ACCT_TYPE_BANK; type < NUM_ACCOUNT_TYPES; ++type)
     {
-        GNCAccountType child;
         if (type == ACCT_TYPE_ROOT)
         {
             loghandler = g_log_set_handler (logdomain, loglevel,
@@ -2278,11 +2277,11 @@ test_xaccAccountType_Compatibility (void)
             g_assert_cmpint (compat, == , equity_compat);
         else if (type == ACCT_TYPE_TRADING)
             g_assert_cmpint (compat, == , trading_compat);
-        for (child = ACCT_TYPE_NONE; child < ACCT_TYPE_LAST; child = ++child)
-            if (1 << child & compat)
-                g_assert (xaccAccountTypesCompatible (type, child));
+        for (auto parent = ACCT_TYPE_NONE; parent < ACCT_TYPE_LAST; ++parent)
+            if (1 << parent & compat)
+                g_assert (xaccAccountTypesCompatible (parent, type));
             else
-                g_assert (!xaccAccountTypesCompatible (type, child));
+                g_assert (!xaccAccountTypesCompatible (parent, type));
 
         compat = xaccAccountTypesCompatibleWith (type);
         if (type <= ACCT_TYPE_LIABILITY ||