Install the fuzzer:

go get -u github.com/dvyukov/go-fuzz/go-fuzz github.com/dvyukov/go-fuzz/go-fuzz-build

Update OPA mod file to point to local repo:

go mod edit -replace github.com/open-policy-agent/opa=$(go env GOPATH)/src/github.com/open-policy-agent/opa

Build the fuzzer package. The fuzzer package includes the code to run and the corpus:

go-fuzz-build github.com/open-policy-agent/fuzz-opa

Run the fuzzer:

go-fuzz -bin=fuzz-fuzz.zip -workdir=workdir

The last command will start the fuzzer and output the results to the workdir.

See go-fuzz/README.md for details on the fuzzer output. Pay attention to the restarts output field. This value should be around 1/10,000. If it's higher than this and the crashers field is greater than zero, check the output directory for crash output.

Or just make, with optional path for OPA source like:

make OPA_TARGET=/path/to/opa/src/dir