[GNC] Tax Invoice & Australian Tax Invoice Total Discount Bug

[Jeff]

Hi List,

I am in the process of upgrading to the latest version of GnuCash, but 
have found a bug in the Tax Invoice Report file "taxinvoice.eguile.scm.  
This effects both the standard Tax Invoice and Australian Tax Invoice as 
they both use the same scm file.

The Discount Total on the report always equates to ZERO.

I have tried googling, but have not found any other reports of this 
error, although I do seem to recall running into it a few years ago.

I have been running GnuCash 2.6 (yes, I know, VERY old, but it works for 
me) where the report worked fine.  I'm not sure about the 3.x release, 
but so far all of the 4.x releases I've tried all have the same issue.

The report in 2.6 actually calculated the Discount Total by adding each 
Discount line item amount together.  The report line (310) was:
      (dsc-total (gnc:make-commodity-collector))

The report has been updated some time ago that it now calculates the 
Discount Total, but the equation is wrong as it always equates to zero.  
Unfortunately BOTH files state it is:
- Version 0.03
- Modified Date: 16 Feb 2012

Surely other people are using the Invoice report to send Invoices with 
discounts?  This bug couldn't have been around unnoticed since 2012, or 
is there a setting that I've missed?

Line 301 in the "new" file now has the following calculation:
     (dsc-total (- inv-total tax-total sub-total))

However, The Invoice Total - Tax Total - Sub-Total will always equal 
Zero and does not equate to any discount as those numbers are AFTER the 
discount has been applied.

Example:
             Charge  : $100
             Discount:  $10

             Invoice Total:  $90
             Tax Total    :   $1
             Sub Total    :  $89   (Sub Total is the Total Invoice 
amount Pre-Tax in this report)

             So Invoice Total ($100) - Tax Total ($1) - Sub-Total ($89) = $0
             Nowhere does the Discount Total come into it.

I have reverted back the calculation to be based on adding each line 
item, and it seems to work.  I have attached a PatchFile, just in case 
this issue has been affecting others and they wish to apply the patch, 
or if a maintainer wishes to apply it to the main branch.

I have just based the changes on a 5 minute scheme crash course, mostly 
by looking at the older report file, so there has not been any rigorous 
testing, but it seems to work.

If there is any setting that I should be using that will make the change 
redundant I'd be happy if someone could point it out to me.

Regards,
Jeff.
-------------- next part --------------
--- taxinvoice.eguile.scm_ORIG	2023-02-18 12:08:18.238227981 +1100
+++ taxinvoice.eguile.scm	2023-02-18 12:08:18.228227981 +1100
@@ -298,7 +298,7 @@
       (let* ((inv-total (gncInvoiceGetTotal opt-invoice))
              (tax-total (gncInvoiceGetTotalTax opt-invoice))
              (sub-total (gncInvoiceGetTotalSubtotal opt-invoice))
-             (dsc-total (- inv-total tax-total sub-total))
+             (dsc-total (gnc:make-commodity-collector))
              (total-col (gnc:make-commodity-collector)))
         (total-col 'add currency inv-total)
         (for-each
@@ -314,6 +314,8 @@
                   (acc       (if cust-doc? (gncEntryGetInvAccount entry)(gncEntryGetBillAccount entry)))
                   (taxable   (if cust-doc? (gncEntryGetInvTaxable entry)(gncEntryGetBillTaxable entry)))
                   (taxtable  (if cust-doc? (gncEntryGetInvTaxTable entry)(gncEntryGetBillTaxTable entry))))
+            (dsc-total 'add currency rdiscval)
+            
     ?>
     <tr valign="top">
       <?scm (if opt-col-date (begin ?>
@@ -362,7 +364,7 @@
                     (if (and discount?) 1 0)
         ) ?>"><strong><?scm:d opt-subtotal-heading ?></strong></td>
         <?scm (if discount? (begin ?>
-        <td align="right" class="subtotal"><strong><?scm:d (fmtmoney currency dsc-total) ?></strong></td>
+        <td align="right" class="subtotal"><strong><?scm (display-comm-coll-total dsc-total #f) ?></strong></td>
         <?scm )) ?>
         <?scm (if tax? (begin ?>
           <td align="right" class="subtotal"><strong><?scm:d (fmtmoney currency sub-total) ?></strong></td>