goassets.go is a script to be put in your e.g. go web project for bundling assets into your binary. It is on purpose not a separate application to a) remove external build dependencies (only go and the go stdlib is needed) and b) so that all people building generate the same output.
The final goassets.go file is generated from a 3 files: tpl/goassets-script/tpl/goassets.go, tpl/goassets-tpl/gen.go and tpl/goassets-tpl/compiled.go.tpl
tpl/goassets-tpl/comiled.go.tplis appended to tpl/goassets-tpl/gen.go (it includes go template code so it would not be compilable)const tplintpl/goassets-script-tpl/goassets.gois then replaced with the content oftpl/gen.go+tpl/compiled.go.tpl
The reason for this is to keep tpl/goassets-tpl/gen.go and tpl/goassets-script-tpl/goassets.go compilable to help editing those bits.
go run goassets.go --file assets/assets.go assets
This call will bundle all files found in assets/ into the file assets/assets.go. The recommended interface to access assets is provided vi FileSystem() function which is compatible to http.FileSystem.
Set e.g. assets.DevPath = os.Getenv("GOASSETS_PATH") and start the program with GOASSETS_PATH=/path/to/asset/root to reload all assets from the file system. This way you e.g. do not need to recompile you web server for working on html/css/javascript.
See examples