How to automatically disambiguate identical bibliography keys in custom bibliography style?

Question

I am trying to reproduce my university bibliography style in biblatex.

In the bibliography, every entry is prefixed with label in parentheses which consists of institution or authors, year and cited page (optional). When there are two entries with the same institution or authors and the same year, the year should be suffixed with consecutive letters as pictured below:

At this point, the code generating bibliography looks as follows:

\defbibenvironment{bibliography}{%
  \list{%
    \printtext[parens]{%
      \printlist{institution}%
      \setunit*{\addcomma\addspace}%
      \printnames[author-label][-2]{author}%
      \setunit*{,\addspace}%
      \printfield{year}%
      \iffieldundef{thiscite}{}
        {\addcomma\space\printfield{thiscite}}%
    }%
    \enspace---\enspace%
  }{%
    \setlength{\labelwidth}{\labelnumberwidth}%
    \setlength{\leftmargin}{\labelwidth}%
    \setlength{\labelsep}{0pt}%
    \addtolength{\leftmargin}{\labelsep}%
    \setlength{\itemsep}{\bibitemsep}%
    \setlength{\parsep}{\bibparsep}}%
    \renewcommand*{\makelabel}[1]{\hss##1}
}{\endlist}{\item}

…which produces the following:

I was only able to find partial snippets in the biblatex documentation, but there was no concrete example, so I was not able to make anything out of it.

How can I check if there are two labels with the same institution/authors and year and insert suffix after the year?

MWE

wsb.bbx:

\ProvidesFile{wsb.bbx}[2020/01/11 WSB bibliography style]

\RequireBibliographyStyle{standard}

\DeclareDatamodelFields[type=field, datatype=range, skipout=false]{thiscite}
\DeclareFieldFormat{thiscite}{\mkpageprefix{#1}}

\def\printname{\usebibmacro{name:family}{\namepartfamily}{\namepartgiven}{\namepartprefix}{\namepartsuffix}}
\DeclareNameFormat{author-label}{%
  % If there are more than three names, print only the first one
  \ifmorenames%
    {\ifthenelse{\value{listcount}=1}
      {\printname{} \bibstring{andothers}}
      {}}
    {\printname{}}%
}

\DeclareNameFormat{author}{%
  \namepartfamily%
  \ifdefvoid{\namepartgiven}
    {}{\addcomma\space\namepartgiveni}%
  \ifthenelse{\value{listcount}=\value{liststop}}
    {}{\addcomma\space}%
  \usebibmacro{name:andothers}%
}

\defbibenvironment{bibliography}{%
  \list{%
    \printtext[parens]{%
      \printlist{institution}%
      \setunit*{\addcomma\addspace}%
      \printnames[author-label][-2]{author}%
      \setunit*{,\addspace}%
      \printfield{year}%
      \iffieldundef{thiscite}{}
        {\addcomma\space\printfield{thiscite}}%
    }%
    \enspace---\enspace%
  }{%
    \setlength{\labelwidth}{\labelnumberwidth}%
    \setlength{\leftmargin}{\labelwidth}%
    \setlength{\labelsep}{0pt}%
    \addtolength{\leftmargin}{\labelsep}%
    \setlength{\itemsep}{\bibitemsep}%
    \setlength{\parsep}{\bibparsep}}%
    \renewcommand*{\makelabel}[1]{\hss##1}
}{\endlist}{\item}

\newbibmacro*{institution+author+year}{%
  \printlist{institution}%
  \setunit*{\addcomma\addspace}%
  \printnames{author}%
  \setunit{,\addspace}%
  \printfield{year}%
}

\DeclareBibliographyDriver{report}{%
  \usebibmacro{institution+author+year}%
  \newunit\newblock%
  \printfield{title}%
  \setunit{\addcomma\addspace}%
  \iffieldundef{journaltitle}{}
    {\usebibmacro{in:}%
      \printfield{journaltitle}}%
  \setunit{\addcomma\addspace}%
  \printfield{number}%
  \setunit{\addcomma\addspace}%
  \usebibmacro{url+urldate}%
  \setunit{\addcomma\addspace}%
  \printfield{pages}%
  \newunit\newblock%
\finentry}

mve.tex:

\documentclass[]{article}

\usepackage[
    bibstyle=wsb,
    sortcites=true,
    sorting=nty,
]{biblatex}

\usepackage{filecontents}
\begin{filecontents*}{sample.bib}
@report{gus_2016,
    title = "Działalność innowacyjna przedsiębiorstw w~latach 2013-2016",
    institution = "GUS",
    url = "http://stat.gov.pl/obszary-tematyczne/nauka-i-technikaspoleczenstwo-informacyjne/nauka-i-technika/dzialanosc-innowacyjnaprzedsiebiorstw-w-latach-2013-2015,2,14.html",
    urldate = "2017-07-18",
    thiscite = "3",
    year = 2016,
}

@report{gus_2016a,
    title = "Badanie organizacji i~rozkładu czasu pracy w~Polsce w~2015 roku",
    institution = "GUS",
    url = "http://stat.gov.pl/obszary-tematyczne/rynekpracy/opracowania/badanie-organizacji-i-rozkladu-czasu-pracy-wpolsce-w-2015-r-,12,1.html",
    urldate = "2017-07-18",
    thiscite = "38",
    year = 2016,
}
\end{filecontents*}
\addbibresource{sample.bib}

\begin{document}
Citation number one \cite{gus_2016}.

Citation number two \cite{gus_2016a}.

\printbibliography{}
\end{document}

Answer 1

I suggest you base your style on authoryear or one of its derivatives. biblatex (or rather Biber/BibTeX) automatically calculate uniqueness information for author/editor-year combinations and make them available in the extradate field (which is automatically printed with \printlabeldateextra, \printdateextra and friends).

Then the repetition of the citation in the bibliography can be implemented as in my biblatex-ext styles (the introcite=plain, feature). This made it possible to remove a few now unused macros.

There are some smaller changes to the style as well

• It is good practice to make sure that all bibliography drivers start with \usebibmacro{bibindex}\usebibmacro{begentry} and end with \usebibmacro{finentry}.
• Data model commands need to be in a separate .dbx file.

Finally, I changed the field for GUS in the example entries from institution to author. author and editor are functional roles, so if the author was an institution, there is no reason not to include it there. The institution and organization fields are similar in role to the publisher field. Compare also If no author use organization or institution.

In total (with .bbx, .cbx, .dbx file produced by inline filecontents to make the example self contained)

\documentclass[polish]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\begin{filecontents}{wsb.bbx}
\ProvidesFile{wsb.bbx}[2020/01/24 WSB bibliography style]

\RequireBibliographyStyle{authortitle}

\DeclareFieldFormat{thiscite}{\mkpageprefix{#1}}

\newbibmacro*{bbx:introcite}{\usebibmacro{cite}}

\newcommand*{\extblx@introcite@init}{%
  \iftoggle{blx@citation}
    {}
    {\togglefalse{blx@bibliography}%
     \toggletrue{blx@citation}}%
  \delimcontext{bbx@introcite}%
  \csuse{blx@hook@cite}%
  \csuse{blx@hook@citekey}%
  \DeclareFieldFormat{bibhyperref}{##1}%
  \undef\cbx@lasthash
  \undef\cbx@lastyear
  \citetrackerfalse\pagetrackerfalse\backtrackerfalse
  \defcounter{maxnames}{\blx@maxcitenames}%
  \defcounter{minnames}{\blx@mincitenames}%
}

\newbibmacro{introcite:typeset}{%
  \begingroup
    \extblx@introcite@init
    \printtext[bbx@introcite]{\usebibmacro{bbx:introcite}}%
  \endgroup
}

\newbibmacro{introcite:plain}{%
  \usebibmacro{introcite:typeset}%
  \printunit*{\introcitepunct}}

\DeclareFieldFormat{bbx@introcite}{\mkbibparens{#1}}
\newcommand*{\introcitepunct}{\enspace---\enspace}%

\renewbibmacro{begentry}{%
  \usebibmacro{introcite:plain}}


\newbibmacro*{institution+author+year}{%
  \printlist{institution}%
  \setunit*{\addcomma\space}%
  \printnames{author}%
  \setunit{\addcomma\space}%
  \printdate
}

\DeclareBibliographyDriver{report}{%
  \usebibmacro{bibindex}%
  \usebibmacro{begentry}%
  \usebibmacro{institution+author+year}%
  \newunit\newblock%
  \printfield{title}%
  \setunit{\addcomma\addspace}%
  \iffieldundef{journaltitle}
    {}
    {\usebibmacro{in:}%
      \printfield{journaltitle}}%
  \setunit{\addcomma\addspace}%
  \printfield{number}%
  \setunit{\addcomma\addspace}%
  \usebibmacro{url+urldate}%
  \setunit{\addcomma\addspace}%
  \printfield{pages}%
  \newunit\newblock%
  \usebibmacro{finentry}}

\endinput
\end{filecontents}

\begin{filecontents}{wsb.cbx}
\ProvidesFile{wsb.cbx}[2020/01/24 WSB citation style]

\RequireCitationStyle{authoryear}

\ExecuteBibliographyOptions{autocite=inline}

\DeclareDelimFormat{nameyeardelim}{\addcomma\space}

\endinput
\end{filecontents}

\begin{filecontents}{wsb.dbx}
\ProvidesFile{wsb.dbx}[2020/01/24 WSB bib/cite style data model]

\DeclareDatamodelFields[type=field, datatype=range, skipout=false]{thiscite}

\DeclareDatamodelEntryfields{thiscite}

\endinput
\end{filecontents}

\usepackage[
  style=wsb,
  sortcites=true,
]{biblatex}

\begin{filecontents*}{\jobname.bib}
@report{gus_2016,
  title       = {Działalność innowacyjna przedsiębiorstw w~latach 2013-2016},
  author      = {GUS},
  url         = {http://stat.gov.pl/obszary-tematyczne/nauka-i-technikaspoleczenstwo-informacyjne/nauka-i-technika/dzialanosc-innowacyjnaprzedsiebiorstw-w-latach-2013-2015,2,14.html},
  urldate     = {2017-07-18},
  thiscite    = {3},
  year        = 2016,
}
@report{gus_2016a,
  title       = {Badanie organizacji i~rozkładu czasu pracy w~Polsce w~2015 roku},
  author      = {GUS},
  url         = {http://stat.gov.pl/obszary-tematyczne/rynekpracy/opracowania/badanie-organizacji-i-rozkladu-czasu-pracy-wpolsce-w-2015-r-,12,1.html},
  urldate     = {2017-07-18},
  thiscite    = {38},
  year        = 2016,
}
\end{filecontents*}
\addbibresource{\jobname.bib}

\begin{document}
Citation number one \autocite{gus_2016}.

Citation number two \autocite{gus_2016a}.

\printbibliography
\end{document}