How to draw a rectangle with only "one" round edge

Question

I need to draw a rectangle with only one round edge like following image.

In this case its south-west corner that is round. I looked up n saw this post

Draw a rectangle with rounded ends in TikZ

but i got error when I did

\node (1) [draw, draw, rounded rectangle, rounded rectangle north east arc=0pt] {rounded rectangle}

which is modified version of (Answer 1: Line 11)

\node (2) [draw, rounded rectangle, rounded rectangle west arc=0pt] {rounded rectangle};

Answer 1

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \draw[sharp corners] (0,0) -- (0,1) -- (1,1)   -- (1,0) [rounded corners] -- cycle;
\end{tikzpicture}
\end{document}

Answer 2

as node with such shape:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{positioning}

    \begin{document}
\begin{tikzpicture}[
oneroundedge/.style = {%
    minimum width=#1,
    minimum height=12mm, text depth=0.25ex,
    outer sep=0pt,
    append after command={
        \pgfextra{\let\LN\tikzlastnode
    \path[draw, fill=gray!30] (\LN.south west) -| (\LN.north east)
        -- (\LN.north west) [rounded corners=3mm] -- cycle;
                       }     },
        font=\bfseries}
                    ]
\node (n1) [oneroundedge=12mm] {};
\node (n2) [oneroundedge=22mm, right=of n1] {text};
\end{tikzpicture}
    \end{document}

it is easy to add more options to oneroundedge style definition (for example for fill). solution with node enable all possibilities of nodes placement, anchoring etc. note: anchor south west is at south west corner of rectangle which underlay define oneroundedge shape.

Answer 3

if you do not need it filled it is possible with simple LaTeX commands:

\documentclass{article}
\unitlength=1cm \thicklines
\begin{document}

\begin{picture}(8,4)
\put(8,4){\oval(16,8)[lb]}
\put(0,4){\line(1,0){8}}\put(8,0){\line(0,1){4}}
\end{picture}

\end{document}

Answer 4

A variation on samcarter's answer, without explicit coordinates of the path:

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \node[minimum width=1.5cm, minimum height=1cm] (a) {};
    \draw[fill=black] (a.south west) -- (a.north west) -- (a.north east) -- (a.south east) [rounded corners=10pt] -- cycle;
\end{tikzpicture}
\end{document}

Answer 5

I saw many accepted answers and decided to give you a solution:

\documentclass{article} 
\usepackage{tikz}

    \begin{document}

          \begin{tikzpicture}
            \draw[black,fill=gray] (0,0)--(3,0)--(3,-2)--(0.2,-2) to[in=270,out=180] (0,-1.8)--cycle;
          \end{tikzpicture}

    \end{document}

It is a manual solution using the command "to" that I think is a useful command. I am sure there are better solution (So, don't accept it yet)