I'm new to pragrammimg. let me handle this issue

Sure! In case you need any additional information, don't hesitate to ask!
I and @tmichalak will be happy to help you

can you assist me in this

Of course! Here is the plugin source file:
https://github.com/SymbiFlow/yosys-symbiflow-plugins/blob/master/xdc-plugin/xdc.cc

First, make sure that you can compile Yosys and run it with the XDC plugin.
This requires setting some options for Yosys, or copying the files manually.

Tomorrow, I can give you more detailed information how to do that and test the plugin.

GitHub

SymbiFlow/yosys-symbiflow-plugins

Plugins for Yosys developed as part of the SymbiFlow project. - SymbiFlow/yosys-symbiflow-plugins

tell me more on how to do that

Here are instructions that will allow you to reproduce my error. I created another branch with the failing syntax, so it will be easier for you to set up a working project.

1. Create a workspace directory:

mkdir yosys_plugins_workspace
cd yosys_plugins_workspace

2. Download, compile, and install yosys. It is also possible to proceed without installing yosys globally but this option requires a more complicated yosys-plugins setup.

git clone https://github.com/symbiflow/yosys
cd yosys
make j$(nproc)
sudo make install
cd ..

3. Download, compile, and install yosys-plugins:

git clone https://github.com/SymbiFlow/yosys-symbiflow-plugins
cd yosys-symbiflow-plugins
make j$(nproc)
sudo make install
cd ..

4. Download the symbiflow-arch-defs repository which contains tests of the symbiflow toolchain and prepare the local conda environment:

git clone --recursive https://github.com/antmicro/symbiflow-arch-defs -b bufgmux_broken
cd symbiflow-arch-defs
export YOSYS=`which yosys`
make env
source env/conda/bin/activate symbiflow_arch_def_base

yosys + yosys_plugins are used in the toolchain synthesis step. Because of that, you can use the examples provided there to check whether your changes work correctly with the prepared synthesis script. You can use your system yosys installation after you set the YOSYS environment variable. The variable has to point to the yosys binary in your system.

5. Run the example to reproduce my errors:

cd build/xc/xc7/tests/bufgmux
make bufgmux_arty_bit

Note that this may take about 1h to generate the FPGA architecture for the chip.
On the other hand, you will be able to use other examples to test your changes.

Make sure that after changing the XDC plugin in the yosys-plugin repository, you built and installed the latest version of your plugin. Please, make sure that your changes can be correctly compiled.