[Tex/LaTex] Only draw part of a borderline in tcolorbox

fancyvrbtcolorbox

I want to tune the type of tcolorbox that I'm making.

I want specifically to only draw a border on one side of the image, similar to how minted allows to draw only a border on one side by specifying option frame=leftline.

I got the following code: 

\documentclass[a5paper]{article}
\usepackage[T1]{fontenc}
\usepackage[]{minted}
\usepackage[skins]{tcolorbox}
\usepackage{lineno}
\def\gobble#1{}
\renewcommand\DeleteFile[1]{}
\usepackage{xparse}
\ExplSyntaxOn
\box_new:N \l_fvrb_box
\tl_new:N \l_fvrb_tl

\RenewDocumentCommand \FancyVerbFormatLine { m }
 {
   \hbox_set:Nn \l_fvrb_box { #1 }
    \dim_compare:nNnTF { \box_wd:N \l_fvrb_box }>{ \linewidth }
      { 
       \tl_set:Nn \l_fvrb_tl { #1 }
       \fvrb_use_tl:N \l_fvrb_tl
      } 
      {%box fits
       \box_use:N \l_fvrb_box
      }
 }

\cs_new:Npn \fvrb_use_tl:N  #1
 {
  \group_begin:
   \null\hfill\vbox_set:Nn \l_fvrb_box
     {\hsize=\linewidth
      \renewcommand\thelinenumber
           {
             \ifnum\value{linenumber}=1\relax\else
                  $\rightarrow$
             \fi
           }
      \begin{internallinenumbers}
        \advance\hsize by -2em
        \hspace*{-2em}\tl_use:N #1
      \end{internallinenumbers}
     }
   \box_use:N \l_fvrb_box
  \group_end:
}
\ExplSyntaxOff
\definecolor{mintedbg}{RGB}{250,255,250}
\usepackage{etoolbox}
\BeforeBeginEnvironment{minted}{\begin{tcolorbox}[enhanced,
width=\linewidth,
enlarge top by=3pt,enlarge bottom by=3pt,
enlarge left by=3pt,enlarge right by=3pt,
frame hidden,boxrule=0pt,top=1mm,bottom=1mm,
colframe=green!30!black, colbacktitle=green!50!yellow,
coltitle=black, colback=mintedbg,
borderline={.8pt}{-0.5pt}{blue!87!green!13, sharp corners},
borderline={.9pt}{-3pt}{blue!70!green!30, sharp corners},
borderline={1pt}{-5.5pt}{blue!53!green!47, sharp corners}]}%
\AfterEndEnvironment{minted}{\end{tcolorbox}}%
\begin{document}
\begin{minted}{latex}
%Preamble
\usepackage[]{minted}
\usepackage[fancyvrb=true]{listings}
\usepackage{tcolorbox}
\usepackage{etoolbox}
\BeforeBeginEnvironment {minted} { \begin{tcolorbox} } \AfterEndEnvironment {minted} { \end{tcolorbox} }%
\usepackage{lipsum}
\end{minted}
\end{document}

Ideally, I'd want a style very similar to minted's frame=leftline, except with multiple (border-)lines as outlined in the example.

Best Answer

One option:

\documentclass[a5paper]{article}
\usepackage[T1]{fontenc}
\usepackage[]{minted}
\usepackage[skins]{tcolorbox}
\usepackage{lineno}
\def\gobble#1{}
\renewcommand\DeleteFile[1]{}
\usepackage{xparse}
\ExplSyntaxOn
\box_new:N \l_fvrb_box
\tl_new:N \l_fvrb_tl

\RenewDocumentCommand \FancyVerbFormatLine { m }
 {
   \hbox_set:Nn \l_fvrb_box { #1 }
    \dim_compare:nNnTF { \box_wd:N \l_fvrb_box }>{ \linewidth }
      { 
       \tl_set:Nn \l_fvrb_tl { #1 }
       \fvrb_use_tl:N \l_fvrb_tl
      } 
      {%box fits
       \box_use:N \l_fvrb_box
      }
 }

\cs_new:Npn \fvrb_use_tl:N  #1
 {
  \group_begin:
   \null\hfill\vbox_set:Nn \l_fvrb_box
     {\hsize=\linewidth
      \renewcommand\thelinenumber
           {
             \ifnum\value{linenumber}=1\relax\else
                  $\rightarrow$
             \fi
           }
      \begin{internallinenumbers}
        \advance\hsize by -2em
        \hspace*{-2em}\tl_use:N #1
      \end{internallinenumbers}
     }
   \box_use:N \l_fvrb_box
  \group_end:
}
\ExplSyntaxOff
\definecolor{mintedbg}{RGB}{250,255,250}
\usepackage{etoolbox}
\BeforeBeginEnvironment{minted}{%
\begin{tcolorbox}[
  width=\linewidth,
  enlarge top by=3pt,
  enlarge bottom by=3pt,
  enlarge left by=3pt,
  enlarge right by=3pt,
  frame hidden,boxrule=0pt,
  top=1mm,
  bottom=1mm,
  colframe=green!30!black, 
  colbacktitle=green!50!yellow,
  coltitle=black, 
  colback=mintedbg,
  freelance,
  arc=0pt,
  outer arc=0pt,
  boxrule=0pt,
  frame code={
    \draw[blue!87!green!13,line width=0.8pt] 
      ([xshift=-0.5pt]frame.north west) -- ([xshift=-0.5pt]frame.south west);
    \draw[blue!70!green!30,line width=0.9pt] 
      ([xshift=-3pt]frame.north west) -- ([xshift=-3pt]frame.south west);
    \draw[blue!53!green!47,line width=0.8pt] 
      ([xshift=-5.5pt]frame.north west) -- ([xshift=-5.5pt]frame.south west);
  }
]}
\AfterEndEnvironment{minted}{\end{tcolorbox}}%
\begin{document}
\begin{minted}{latex}
%Preamble
\usepackage[]{minted}
\usepackage[fancyvrb=true]{listings}
\usepackage{tcolorbox}
\usepackage{etoolbox}
\BeforeBeginEnvironment {minted} { \begin{tcolorbox} } \AfterEndEnvironment {minted} { \end{tcolorbox} }%
\usepackage{lipsum}
\end{minted}
\end{document}

The result:

enter image description here

I changed from enhanced to freelance and used frame code to draw the lines only to the left (I also set arc and outer arc to 0pt); adjust the settings for the \draw commands according to your needs.

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