Difference between revisions of "Custom Reports"

Latest revision as of 23:26, 24 October 2023

This documentation applies from GnuCash Version 5.0. For prior versons use the previous version.

Custom Reports in GnuCash

The term Custom Reports has several contexts in GnuCash:

• Customizing settings for standard reports (Using GnuCash#Saved Report Configurations)
• Combining selected standard reports into one view (Using GnuCash#Custom Multicolumn Report)
• Customized output format for reports (Custom Reports Using Eguile)
• Reports written in the Scheme programming language which are not delivered as part of the standard reports (this page)

If you are not up for coding, you should check the

• report options
• stylesheets and
• stylesheet options and
• file properties.

Possibly there are ways to get what you desire without coding.

If you are ready for coding (and even already firm in Scheme and Guile) then this is the place to contribute.

Introduction

Custom reports can be fairly challenging and while the information presented here is brief it should be enough to get you started. The focus is on enough understanding to change (hack) existing reports.

In the GnuCash project the reports are coded in Scheme, not in C. Understanding Scheme is one of the prerequisites to create new reports. The obvious drawback is that one must learn yet another programming language (if not already familiar with it) but saves the effort of having to alter and build GnuCash's source code.

Guile is used as an interface to get the Scheme code executed during runtime. Again, if not already familiar with it, this is the second piece of work that one has to swallow.

Last, but not least, the API for that sort of thing is not formally specified.

Still reading? Not yet discouraged? Good for you! Thankfully, lots of help is available.

First of all, there is good educational material available on the web to help you learn Scheme and Guile. Secondly, there is a simple sample-report.scm example report specifically written to show you the base layout of a GnuCash report. And finally, this Wiki page will give you some guidance when starting this venture.

Getting Started

This tutorial will give you an overview of GnuCash reports and might give you the confidence to make simple changes to existing reports.

Appreciation of Scheme language

GnuCash reports are written in the Scheme programming language. For a quick introduction try Learn Scheme in 15 minutes using an online scheme repl.

Language details

This tutorial is self-contained but to extend it in reports you'll want to use the following references and learn about the language. Just be aware of them for now.

Get to know Scheme

• Mastering Scheme is much easier if you've read The Scheme Programming Language by R. Kent Dybvig.

If you are new to Scheme it is not necessary to read and understand all of it right now. For anything more than this tutorial you should, at least, have gone through the Getting Started section.

Get to know Guile

Guile is used internally by GnuCash to interpret the Scheme reports.

• Guile documentation

This comes with a marvelous Tutorial. You don't need this for writing the reports themselves, but it gives a clue of how reports are created in GnuCash. This should be good motivation to go and tackle the learning curve for Scheme.

Get to know Gettext

That is the tool which makes the strings translatable. (G_ "Some Text"), (N_ "Some Text") and similar mark the text for translation. See I18N#How to make strings in code translatable for details.

Where to find existing reports

The location of existing reports varies with by operating systems. The guile path can be found in Help -> About -> GNC_DATA by selecting the parent folder.:

Study some example reports

sample-report

sample-report.scm was created in GnuCash V5.0 from hello-world.scm to demonstrate the basic structure of a report. Don't get too confused by the huge number of options that are shown in this report - they were added to show off the variety of options available in GnuCash.

Have a look under #Where to find existing reports to find the source code for this report. Alternatively, you can browse the current source code for this report on github.

By looking at the result of this report while you study the source code, you will easily get clues to how it functions. You can run this report in GnuCash via the menu: Reports -> Examples -> Sample Report

account-piecharts

If you want to walk through a much more complicated report, study account-piecharts.scm.

There are two long functions in this report.

1. option-generator defines the options for this report.
2. piechart-renderer makes all the calculations and renders the pie chart.

The list of values to be shown in the pie chart can be calculated in two ways - depth-based or via a method that traverses all accounts. The decision for this is made when calling the piechart-renderer function. Both methods will work from a list of selected accounts stored in the topl-accounts variable.

traverse-accounts is a recursive function that calls itself to traverse through all child accounts in the account tree. To get the balance for a single account, it makes a call to profit-fn. profit-fn obtains the account balance for either one interval or at a given date. It calls out to gnc:account-get-comm-balance-at-date in report-utilities.scm where, finally, lower level calls are made, which create a query for the account balance at the given date.

Well, long story short, this report is rather involved. Sorry.

Setup a prototype report

Even if you haven't ever written a report before, and you don't have a shiny track record of great Scheme experience, setting up a prototype at this moment will have the benefits getting productive after some time of pure theory.

The beginners amongst us might not have a final picture of what report to write. No worries, take the sample-report.scm report source file, store it in your preferred working directory, and rename it to a unique name, say my-world.scm. As, for sure, you already have read through this report, you know that this report is very wordy, giving a lot of text printouts. These can be used to easily see your own first changes on the screen once this prototype is loaded into GnuCash, and even better, it will let you differentiate between the my-world.scm that you have loaded and the sample-report.scm that is available in GnuCash by default (see previous section). So feel free to implement some fancy printout changes.

Prerequisites

GnuCash will not be able to load your report until you make changes in two areas of your report source file:

Give report a unique symbol name

To avoid symbol definition conflicts with other reports, make sure your report code begins with a define-module statement with a report name not used by any other report, for example:

(define-module (gnucash report my-world-report))

Define report with unique name and id

To enable GnuCash to register your report into the Report menu, scroll to the end of the code and update the gnc:define-report statement.

Set the name of your report to be shown in the Report menu. This name must be unique across all reports.

'name (N_ "My World")

Further down below, if it is present, comment out the menu-name line:

;;'menu-name (N_ "Sample Report with Examples")

Update the tool tip text to something appropriate for your report:

'menu-tip (N_ "Unstable. Used for Testing.")

Your report must have a globally unique identifier (guid). GnuCash will fail to start if multiple reports have the same unique id. For this reason, if you wish to create a backup of a report while you work on it, place the backup outside the GnuCash directories. If you need some newly generated unique id, use an online uuid generator like this one (any other one will do as well). Be sure to untick "Hyphens" to generate gnucash compatible guids. If you forget or the site you use doesn't offer that option, simply remove the hyphens yourself.

uuidgen | sed -e 's/-//g'

Copy the newly generated ID and paste it into the report-guid value:

'report-guid "paste generated report unique id here"

Loading Your Report

There are two ways to load a report at startup of GnuCash:

• from a user account or
• from the installation tree.

You will likely want to use the user account approach - a least until your work is finished.

Load the report from a user account

This method is used if you edit your report source file in a working directory.

• Edit GNC_CONFIG_HOME/config-user.scm to add a line of the form:

(load (gnc-build-userdata-path "my-world.scm"))

Notes

• (gnc-build-userdata-path ...) or (gnc-build-dotgnucash-path ...) will complement your report name with the full path of your GNC_DATA_HOME or DOT_GNUCASH_DIR directory respectively. If you are comfortable with file locations you could equally well use the form

(load "<absolute path to>/my-world.scm")

to load your report from any arbitrary location on your file system.

• The instructions refer to two separate directories: GNC_CONFIG_HOME and GNC_DATA_HOME. Be careful to use the proper one in the different locations as indicated.
• If the config.user or config-user.scm file is not yet found in your settings directory, simply create it.

Move, copy, or link* your report file (my-world.scm) from your working directory to the proper GNC_DATA_HOME or DOT_GNUCASH_DIR directory. The report should be visible in the Reports menu after the next restart.

* On Unix-like OSs you can use the ln command; on Windows (7 and higher) you can use the mklink command.

To reload your report, you must restart GnuCash. You will have to do this every time you change a report.

Load the report from the installed report directory

While not recommended you can also copy the report to the installed report directory. Make sure you have included a module definition as shown above. All *.scm files from the gnucash/scm/gnucash/report/standard-reports/ directory will be loaded automatically. This applies only to the standard-reports/ sub-directory, not to any of the other directories with reports. Hence, the easiest way to have your report available to gnucash is to copy your *.scm file into that directory.

Note

In case of an eguile based report only the foo.scm file should be stored in the standard-reports directory. The accompanying foo.eguile.scm and foo.css should go in to gnucash/scm/gnucash/report instead.

Then restart GnuCash. You will have to do this every time you change the report definition file.

Debugging your report

When guile cannot make sense of your report, or your report throws an error, GnuCash will present the following error message in place of your report:

This lets you know there was a problem, but now you need to pinpoint where the problem lies. Here are some tips that might help.

gnucash --debug --log gnc.scm=debug

/Applications/Gnucash.app/Contents/MacOS/Gnucash --debug --log gnc.scm=debug

find /var/folders -name "gnucash.trace" 2> /dev/null

(gnc:debug "here I am")

Although guile does have debug support, this wiki page updater has not found a way, at this time, to hook GnuCash up to the guile debugger.

Development Environment

Programming tools

Any reasonable source/text editor, including emacs and vi, should provide basic syntax support for source-code editing. One of the most basic and important for editings scheme/lisp sources is parenthesis matching. Other scheme-like environments (such as DrRacket) might also be useful for editing the sources, but note that they might allow constructs that are not valid in guile. Beware Racket is a scheme dialect not 100% compatible with Guile, but provides a nice GUI for understanding scheme functions.

Simple Proposal for Linux

This is a simple proposal for a development environment in Linux. Assume

• there is a working directory ~/GnuCash/CustomReports in your home directory.
• the new report is stored in the test00.scm file

Here is the proposal how to setup up your environment

cd ~/GnuCash/CustomReports
ln -s test00.scm prototype.scm
cat > config.user << "EOF"
(load "<fullPathTo>/GnuCash/CustomReports/prototype.scm")
EOF
cd ~/.gnucash
ln -s ~/GnuCash/CustomReports/config.user
uuidgen | sed -e s/-//g

Prepare test00.scm to include

• the define-module statement

(define-module (gnucash report prototype-report))

• following updates in the gnc:define-report statement

'name (N_ "Prototype")
;;'menu-name (N_ "Sample Report with Examples")
'menu-tip (N_ "Unstable. Used for Testing.")
'report-guid "the-new-generated-unique-ID"

See also the minimum report defintion in the #Designing new Reports chapter.

By this you can

• use test00.scm as a template test report and use the lines as described above without further changes
• collect all our test reports as e.g. testXX.scm files in this directory
• switch between them by making the prototype.scm point to the desired report
• restart GnuCash
• always find the report under Reports->Sample & Custom Report->Prototype

Finally, you should also extract a GnuCash source tar ball in ~/GnuCash/CustomReport/ to have access to the Scheme files referenced in this page.

Technique to reload reports without restarting GnuCash

Reports can be modified to allow the majority of the report to be reloaded without requiring GnuCash to be restarted for each change which is very convenient when developing reports. This requires splitting the report into two files:

1. a minimal loader which which forces the reload of the meat of your report each time options are generated or report is rendered.
2. the meat of your report. This contains actual report code for the options generator and renderer.

Both files must parse and execute correctly before the reload will function.

Note that, at least in GnuCash 2.6.17, for changes to report options to take effect, the report must closed and then relaunched from the Report menu. Changes to the render portion seem to be handled just fine by the reload button.

Minimal Example

The following is a skeleton outline of what is required for a report to be reloaded on the fly. Tested with GnuCash 2.6.17.

WARNING

This section is out of date and will not run with GnuCash ≥ 4.6

Minimal Loader

Update name, report-guid and menu-tip values appropriately for your report.

custom_import.scm:

(define-module (custom_import))
(use-modules (gnucash gnc-module))
(use-modules (gnucash gettext))
(gnc:module-load "gnucash/report/report-system" 0)
; load the renderer module once at the top level to get the symbols
(use-modules (custom_import_renderer))

; get and reload the module
(define (reload-report-module)
  (reload-module (resolve-module '(custom_import_renderer))))

; every time options are generated, reload the meat of the report
(define (options_loader)
  (reload-report-module)
  (custom_import_options))

; every time report is rendered, reload the meat of the report
(define (renderer_loader report-obj)
  (reload-report-module)
  (custom_import_renderer report-obj))
 
(gnc:define-report
 'version 1
 'name (N_ "<type your report name here>")
 'report-guid "<paste report unique id here>"
 'menu-tip (N_"<type your report menu tip here>")
 'menu-path (list gnc:menuname-utility)
 'options-generator options_loader
 'renderer renderer_loader)

The Meat of Your Report

custom_import_renderer.scm:

(define-module (custom_import_renderer))
 
; options for the report (called by loader after it reloads this module)
(define (custom_import_options)    
  (let* ((options (gnc:new-options)))  
    ; add your options here       
    options))
 
; report renderer (called by loader after it reloads this module)
(define (custom_import_renderer report-obj) 
  (let ((document (gnc:make-html-document)))
      ; add your renderer here
      document))

(export custom_import_options)
(export custom_import_renderer)

Configuration

You'll also need to edit config.user so that GnuCash can find the files above. Update add-to-load-path value appropriately for your setup.

config.user:

(add-to-load-path "<type the full path to above report files here>")
(use-modules (custom_import))

Designing new Reports

In general, reports are divided into three sections

• the Options-Generator (define the options for the report)
• the Report-Renderer (create the HTML report)
• the gnc:define-report statement (makes the report available in GnuCash)

This is the minimum definition needed for a new GnuCash report. Update name, report-guid^[2] and menu-tip values appropriately.

prototype.scm:

;; -*-scheme-*-

;; This is a minimum report definition in GnuCash.
;; It illustrates the the minimum definitions needed to create
;; a new GnuCash report.
;; It will create an empty page with heading 'Prototype'.
;; To be used as template.

;; ------------------------------------------------------------------
;; Top-level definitions
;; ------------------------------------------------------------------

(define-module (gnucash reports example prototype))

(use-modules (gnucash engine))
(use-modules (gnucash utilities)) 
(use-modules (gnucash core-utils))
(use-modules (gnucash app-utils))
(use-modules (gnucash report))
(use-modules (gnucash html))

(debug-enable 'backtrace)

;; ------------------------------------------------------------------
;; Define the Options for this report
;; ------------------------------------------------------------------

(define (options-generator)    
  (let* ((options (gnc-new-optiondb)))         
    options))

;; ------------------------------------------------------------------
;; Render the HTML document
;; ------------------------------------------------------------------

(define (document-renderer report-obj)
  ;; Helper function for looking up option values
  (define (get-option section name)
    (gnc-optiondb-lookup-value (gnc:report-options report-obj) section name))

  (let* (
         (doc (gnc:make-html-document))
         (report-title (get-option gnc:pagename-general
                                   gnc:optname-reportname))
		)

        (gnc:html-document-add-object!
         doc
         (gnc:make-html-text
          (gnc:html-markup-h3
           (format #f (G_ "~a")
                   report-title))))
    doc))
 
;; ------------------------------------------------------------------
;; Define the actual report
;; ------------------------------------------------------------------

(gnc:define-report
 'version 1
 'name (N_ "Prototype")
 'report-guid "<paste generated unique report id here>"
 'menu-tip (N_ "Unstable. Used for Testing.")
 'menu-path (list gnc:menuname-example)
 'options-generator options-generator
 'renderer document-renderer)

The Options-Generator

Each report takes responsibility to build up an own database that holds the options for the report.

Usually it is a good habit to copy the relavant code from the sample-report.scm. In there you will find the code initializing the database and filling it with options:

(define (options-generator)    
  (let* ((options (gnc-new-optiondb)))         
    options))

Options are directly registered in the option database with a call to gnc-register-<type>-option.

sample-report.scm presents a nice selection of example option definitions of the following types:

gnc-register-simple-boolean-option
gnc-register-multichoice-option
gnc-register-string-option
gnc-register-date-option-set
gnc-register-number-range-option
gnc-register-color-option
gnc-register-account-list-option
gnc-register-list-option

Elsewhere you find:

gnc-register-text-option
gnc-register-font-option
gnc-register-currency-option
gnc-register-budget-option
gnc-register-commodity-option
gnc-register-complex-boolean-option
gnc-register-pixmap-option 
gnc-register-account-list-limited-option
gnc-register-account-sel-option
gnc-register-account-sel-limited-option
gnc-register-multichoice-callback-option
gnc-register-radiobutton-option
gnc-register-radiobutton-callback-option
gnc-register-internal-option
gnc-register-query-option
gnc-register-dateformat-option

Also, business options:

gnc-register-invoice-option
gnc-register-customer-option
gnc-register-vendor-option
gnc-register-employee-option
gnc-register-owner-option
gnc-register-taxtable-option
gnc-register-counter-option
gnc-register-counter-format-option

In general, the syntax for creating an option is:

(define (gnc-register-<type>-option opitiondb
         section                      ;; the tab-string in the option dialog presented to the user
         name                         ;; the text for this option in the option dialog presented to the user
         sort-tag                     ;; used to define the order in which the options are listed
         documentation-string         ;; help string shown when the mouse moved over the option
         default-value
         <optional type specific parameters>)

Note that section is free to be any text string. If section-string has not been used before, a new tab with this name will be created automatically. Nevertheless, note that report-core.scm provides three default names. Re-use these before creating new names:

(define gnc:pagename-general (N_ "General"))
(define gnc:pagename-accounts (N_ "Accounts"))
(define gnc:pagename-display (N_ "Display"))

For a start, simply read through the define (options-generator) statement in sample-report.scm and copy what you need.

Nice to know:

• The General option group does not need to be defined, it is part of the report definition per default. If you run the above minimum report definition, the General option group will automatically include a text field for the Report Name, a selection box for the Stylesheet, and a button to Reset defaults.
• The guile path can be found in Help -> About -> GNC_DATA by selecting the parent folder.

The Report-Renderer

Define how to apply the options (the actual report contents).

The overall goal of the Report-Renderer is to create an HTML-document and fill it with the report results to display to the user. You should refer to the HTML generation description documentation in the source code.

Similar to Options-Generator, sample-report.scm gives you a great introduction to how this works in general.

The gnc:...-procedures are found in the src/report/report-system/html-*.scm source files.

After runnning the report you can press the Export button to save the generated HTML-Code into a file for viewing. Doing this for the above minimum prototype report gives the following result:

<!DOCTYPE html>
<html dir='auto'>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<style type="text/css">
@media (prefers-color-scheme: dark) {body {color: #000; background-color: #fff;}}
h3 { font-family: "Segoe UI", sans-serif; font-size: 15pt; font-weight: bold;  }
a { font-family: "Segoe UI", sans-serif; font-size: 10pt; font-style: italic;  }
body, p, table, tr, td { vertical-align: top; font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
tr.alternate-row { background: #ffffff }
tr { page-break-inside: avoid !important;}
html, body { height: 100vh; margin-top: 0px; margin-bottom: 0px; margin-left: 8px; margin-right: 8px; }
td, th { border-color: grey }
th.column-heading-left { text-align: left; font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
th.column-heading-center { text-align: center; font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
th.column-heading-right { text-align: right; font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
td.highlight {background-color:#e1e1e1}td.neg { color: red;  }
td.number-cell, td.total-number-cell { text-align: right; white-space: nowrap; }
td.date-cell { white-space: nowrap; }
td.anchor-cell { white-space: nowrap; font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
td.number-cell { font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
td.number-header { text-align: right; font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
td.text-cell { font-family: "Segoe UI", sans-serif; font-size: 10pt;  }
td.total-number-cell { font-family: "Segoe UI", sans-serif; font-size: 10pt; font-weight: bold;  }
td.total-label-cell { font-family: "Segoe UI", sans-serif; font-size: 12pt; font-weight: bold;  }
td.centered-label-cell { text-align: center; font-family: "Segoe UI", sans-serif; font-size: 12pt; font-weight: bold;  }
sub { top: 0.4em; }
sub, sup { vertical-align: baseline; position: relative; top: -0.4em; }
@media print { html, body { height: unset; }}
</style></head><body bgcolor="#ffffff"><h3>Report name</h3>
</body>
</html>

The style section is added automatically without specific definitions inside the prototype source. Also note that the register name in GnuCash is not part of the HTML document.

The procedures to fill this HTML-document with life and further formatting are given in the following report/ source files:

html-acct-table.scm
html-barchart.scm
html-document.scm
html-fonts.scm
html-linechart.scm
html-piechart.scm
html-scatter.scm
html-style-info.scm
html-style-sheet.scm
html-table.scm
html-text.scm
html-utilities.scm

Start making the prototype report a little nicer by adding the following line to the document-renderer from html-document.scm

(gnc:html-document-set-title! document (_ "GnuCash Report Prototype"))

will result in an update of the title and h3 lines:

[...]
<title>GnuCash Report Prototype</title>
[...]
<h3>GnuCash Report Prototype</h3>
[...]

Next it is possible to add attributes to the body line.

The body-tag can be enhanced with attributes via the gnc:html-document-set-style! funtion. The general sytax:

(gnc:html-document-set-style!
    document                               ;; the reference to the current html-document
    "body"                                 ;; specify the tag to add attributes to
    'attribute (list "blabla" "balabala")  ;; first additional attribute
    'attribute (list "nonstop" "nonsens")  ;; second additional attribute
    'attribute (list "bgcolor" "#f6ffdb")  ;; third additional attribute
    [...]                                  ;; further attributes
)

The example above lists some imaginary attributes to indicate that the attribute definition will be added to the body-tag without further validity check. Invalid attributes will appear in the HTML-code but will have no visible effect on the document representation.

The rest of the body is filled with HTML-text by defintion of text objects, which gives the following structure

<body bgcolor="#ffffff">
<h3>[title]</h3>

  [text object 1]
  [text object 2]
    .     .    .
    .     .    .
    .     .    .
  [text object n]

</body>

whereas it does not matter if you define one or more text objects, you can put everything into one object or split it over several objects.

In Scheme these objects are defined like

(gnc:html-document-add-object!
    document               ;; the overall HTML document defined above
    (gnc:make-html-text    ;; a text object
        [text 1]             ;; part 1 of the text
        [text 2]             ;; part 2 of the text
             .   .
             .   .
             .   .
        [text m]             ;; part m of the text
    )
)

Note the above structure is the definition of 1 text object, which consists of m (sub-)text elements.

The text elements can be simple strings, or markup-formatted. Markup-commands are found in html-text.scm:

gnc:html-markup-p        ;; markup for "paragraph"
gnc:html-markup-tt       ;; markup for fixed font (type writer style)
gnc:html-markup-em       ;; markup for "emphasis"
gnc:html-markup-b        ;; markup for "bold"
gnc:html-markup-i        ;; markup for "italic"
gnc:html-markup-h1       ;; markup for headers on level 1
gnc:html-markup-h2       ;; markup for headers on level 2
gnc:html-markup-h3       ;; markup for headers on level 3
gnc:html-markup-br       ;; markup for line "break" (no text)
gnc:html-markup-hr       ;; markup for "horizontal line" (no text)
gnc:html-markup-ul       ;; markup for "unsorted list" (bullet list)
gnc:html-markup-anchor   ;; markup for hyperlinks
gnc:html-markup-img      ;; markup for images

To give you a basic idea, an example of simple text objects:

(gnc:html-document-add-object!
     document
     (gnc:make-html-text 
        "some text" 
        "some other text" 
        (gnc:html-markup-br)
        (gnc:html-markup-tt "tt text")
        (gnc:html-markup-h1 "header1 text")
        (gnc:html-markup "bla" "tirili flöt")
        (gnc:html-markup "i" "italic text")
    )
)

results in following HTML-code

<body bgcolor="#f6ffdb">
<h3>GnuCash Report Prototype</h3>
some text some other text
<br />
<tt>tt text</tt>
<h1>header1 text</h1>
<bla>tirili flöt</bla>
<i>italic text</i>
</body>

Note that it is possible to define new tags (here: "bla") if needed by using gnc:html-markup.

Again: Take a good look at sample-report.scm and explore many more examples how to format HTML-text.

Examine:

html-scatter.scm
html-acct-table.scm
html-piechart.scm
html-table.scm
html-linechart.scm

to find out more about

gnc:make-html-scatter
gnc:make-html-acct-table
gnc:make-html-barchart
gnc:make-html-table
gnc:make-html-linechart

The gnc:define-report Statement

If you want to follow the #Simple Proposal for Linux to setup a simple development environment then you need updates to this section only

• once that you set up the development environment
• once that your report is ready, fully tested, and shall become part of your standard reports

And again, sample-report.scm already proposes how you should proceed in the latter case

[...] 
to contribute your brand new, totally cool report, consult the mailing list "mailto:gnucash-devel@gnucash.org"
[...]

Barcharts

The minimum definition of a bar chart report is shown in the following example based on a simple tutorial for generating charts using html-chart.scm. Before running, update name, report-guid and menu-tip values appropriately.

;; -*-scheme-*-

;; This is a minimum report definition in GnuCash.
;; It illustrates the the minimum definitions needed to create
;; a new GnuCash report.
;; It will create an empty page with heading 'Prototype'.
;; To be used as template.

;; ------------------------------------------------------------------
;; Top-level definitions
;; ------------------------------------------------------------------

(define-module (gnucash reports example prototype))

(use-modules (gnucash engine))
(use-modules (gnucash utilities)) 
(use-modules (gnucash core-utils))
(use-modules (gnucash app-utils))
(use-modules (gnucash report))
(use-modules (gnucash html))

(debug-enable 'backtrace)

;; ------------------------------------------------------------------
;; Define the Options for this report
;; ------------------------------------------------------------------

(define (options-generator)
  (gnc-new-optiondb))

;; ------------------------------------------------------------------
;; Render the HTML document
;; ------------------------------------------------------------------

(define (document-renderer report-obj)
  (let (
        (doc (gnc:make-html-document))
        (chart (gnc:make-html-chart))
       )

       (gnc:html-chart-set-title! chart "title")
       (gnc:html-chart-set-type! chart "bar")
       (gnc:html-chart-set-width! chart '(pixels . 800))
       (gnc:html-chart-set-height! chart '(pixels . 600))
       (gnc:html-chart-set-y-axis-label! chart "yAxis")
       (gnc:html-chart-set-data-labels! chart '("a" "b" "c"))
       (gnc:html-chart-add-data-series! chart "series1" '(20 40 30) "red")
       (gnc:html-chart-add-data-series! chart "series2" '(30 25 25) "green")
       (gnc:html-chart-set! chart '(options chartArea backgroundColor) "wheat")
	   
       (gnc:html-document-add-object!
        doc
        (gnc:make-html-text
         (gnc:html-markup-h3
          (format #f (G_ "~a")
               N_ "Demonstration"))))

       (gnc:html-document-add-object! doc chart)

       doc
  )
)

;; ------------------------------------------------------------------
;; Define the actual report
;; ------------------------------------------------------------------

(gnc:define-report
 'version 1
 'name (N_ "Prototype")
 'report-guid "<paste generated unique report id here>"
 'menu-tip (N_ "Unstable. Used for Testing.")
 'menu-path (list gnc:menuname-utility)
 'options-generator options-generator
 'renderer document-renderer)