CMake Error at flutter/CMakeLists.txt:85 (add_custom_command): add_custom_command called with OUTPUT containing a "#". This character is not allowed.
Launching lib\main.dart on Windows in debug mode... lib\main.dart:1 CMake Error at flutter/CMakeLists.txt:85 (add_custom_command): add_custom_command called with OUTPUT containing a "#". This character is not allowed. Exception: Unable to generate build files Exited (sigterm)
As pointed out in comments by @Ṃųỻịgǻňạcểơửṩ, make sure that there's no # character in any of the directories in your path to where the Flutter project is located. For example if you have path like this;
C:\\projects\ui#\your_project
then you will get the error like the one you described. In this case you have to change the name of the direcory ui# to something that does not contain the # character, e.g., ui, so that the path become
C:\\projects\ui\your_project
