pgfkeys-handler-patch.tex

\RequirePackage{pgfkeys}
\RequirePackage{xpatch}

\makeatletter
% usage:
%   <key>/.patch code={search}{replace}
% similar to def of /handlers/.add code/.code 2 args={...}
\pgfkeys{/handlers/.patch/.code 2 args=%
  % Find out, whether with args or not.
  \pgfkeysifdefined{\pgfkeyscurrentpath/.@args}%
  {% Yes, so add to body and reuse args
    \pgfkeyspatchvalue{\pgfkeyscurrentpath/.@body}{#1}{#2}%
    % Redefine code
    {%
      \pgfkeysgetvalue{\pgfkeyscurrentpath/.@args}{\pgfkeys@tempargs}%
      \pgfkeysgetvalue{\pgfkeyscurrentpath/.@body}{\pgfkeys@tempbody}%
      \def\pgfkeys@marshal{\expandafter\gdef\expandafter\pgfkeys@global@temp\pgfkeys@tempargs}%
      \expandafter\pgfkeys@marshal\expandafter{\pgfkeys@tempbody}%
    }%
    \pgfkeysifdefined{\pgfkeyscurrentpath/.@@body}{%
      % support for \pgfkeysndefargs:
      \pgfkeyslet{\pgfkeyscurrentpath/.@@body}{\pgfkeys@global@temp}%
    }{%
      % support for \pgfkeysdefargs:
      \pgfkeyslet{\pgfkeyscurrentpath/.@cmd}{\pgfkeys@global@temp}%
    }%
  }{% No, so single argument (simple \pgfkeysdef). Redefine accordingly.
    \edef\pgf@expanded@path{\pgfkeyscurrentpath}%
    {%
      \pgfkeysifdefined{\pgf@expanded@path/.@cmd}{%
        \expandafter\expandafter\expandafter\pgfkeys@temptoks
        \expandafter\expandafter\expandafter{%
        \csname pgfk@\pgf@expanded@path/.@body\endcsname}%
      }{%
        \expandafter\pgfkeys@temptoks\expandafter{%
        \expandafter\pgfkeyssetvalue\expandafter{\pgf@expanded@path}{##1}}%
      }%
      \edef\pgfkeys@temp{\the\pgfkeys@temptoks}%
      \pgfkeyspatchvalue\pgfkeys@temp{#1}{#2}%
      \global\let\pgfkeys@global@temp\pgfkeys@temp
    }%
    \def\pgf@temp{\pgfkeyssetvalue{\pgf@expanded@path/.@body}}%
    \expandafter\pgf@temp\expandafter{\pgfkeys@global@temp}%
    \expandafter\long\expandafter\def\expandafter\pgfkeys@temp\expandafter##\expandafter1\expandafter\pgfeov\expandafter{\pgfkeys@global@temp}%
    \pgfkeyslet{\pgf@expanded@path/.@cmd}\pgfkeys@temp
  }%  
}

% usage:
%   \pgfkeyspatchvalue{<key>}{<search>}{<replace>}
% similar to \pgfkeysaddvalue
\long\def\pgfkeyspatchvalue#1#2#3{%
  \pgfkeysifdefined{#1}{%
    \expandafter\xpatchcmd\csname pgfk@#1\endcsname{#2}{#3}{}
      {\PackageError{pgfkeys}{Patching for key #1 fails}}%
  }{}%
}
\makeatother