Heroku Deployment Error: Cannot detect buildpack - heroku

Question

I'm trying to deploy my Discord Bot to Heroku and I've successfully linked my Github account to Heroku. It can successfully find the repository I'm trying to deploy, but when I try a manual deployment it gives me the error:
! No default language could be detected for this app.
HINT: This occurs when Heroku cannot detect the buildpack to use for this application automatically.
See https://devcenter.heroku.com/articles/buildpacks
! Push failed
My bot is coded in Go, which is supported by Heroku. Could it be that my code has external libraries? If so, how can I add support for those libraries in Heroku? Thank you in advance.

Answer 1

On Heroku projects are compiled / built using so called buildpacks. Specific buildpacks are created for projects using different languages. For Go projects there exists the heroku/go which knows how to get, compile and build Go projects, including getting their dependencies automatically as part of the build process.
The buildpack selection can happen either manually or automatically. You see the error you posted because you have not set any buildpacks manually, and automatic detection failed for you. See reasons below.
Manual buildpack selection
For manual selection, download the Heroku CLI, and execute the following command:
heroku buildpacks:set heroku/go
Note: if you're using heroku cli for the first time, you may need to login using heroku login. Also if your app is not selected by default, you may specify it using the -a or --app argument, e.g.:
heroku buildpacks:set heroku.go -a yourappname
To see selected buildpacks, execute the heroku buildpacks command.
Automatic buildpack detection
Just because a project is using the Go language, the heroku/go buildpack does not get selected automatically.
The actual detection whether heroku/go should be used is done by the script heroku-buildpack-go/bin/detect, the detection logic is:
if test -f "${build}/Godeps/Godeps.json" || # godeps
test -f "${build}/vendor/vendor.json" || # govendor
test -f "${build}/glide.yaml" || # glide
(test -d "${build}/src" && test -n "$(find "${build}/src" -mindepth 2 -type f -name '*.go' | sed 1q)") # gb
then
echo Go
else
exit 1
fi
So basically the Go language is detected and heroku/go buildpack is selected automatically if one of the following file is present in your project:
Godeps/Godps.json; used by godep
vendor/vendor.json; used by govendor
glide.yaml; used by glide
src/*/*/**/*.go; used by GB
Further reading
Official articles about working with Go and Heroku:
Getting Started on Heroku with Go
Heroku Go Support