Like go mod why but for dependencies in go.sum and not in go.mod - will also work around direct dependencies listed as indirect which can happen with the use of replace directives downstream. Understands module argument with and without the version.

goexplain.sh

#!/bin/bash
# Like go mod why but for dependencies in go.sum and not in go.mod - will also
# work around direct dependencies in the graph listed as indirect in go.mod
# which can happen with the use of replace directives downstream. Understands
# module argument with and without the version.
#
# usage: ./goexplain.sh example.com/path/module
# usage: ./goexplain.sh example.com/path/[email protected]

bold=$(tput bold)
normal=$(tput sgr0)
blue=$(tput setaf 4)

function show_why() {
  why_list="$(go mod graph | digraph allpaths $(go list -m) $1  | tr ' ' '\n'  | awk '!x[$0]++' | grep -v $1)"
  echo "${why_list}"
  second_one="$(echo "${why_list}" | head -2 | tail -1)"
  if grep "${second_one/@/ }" go.mod | grep indirect > /dev/null; then
    echo "${bold}> explaining indirect dependency:${normal}"
    go mod why -m ${second_one/@*/}
  fi
}

if echo $1 | grep "@" > /dev/null; then
  show_why $1
else
  for d in $(go mod graph | grep ${1}@ | gsed -e "s|.*\($1@[^ ]\+\).*|\1|" | awk '!x[$0]++'); do
    echo "${bold}${blue}>> chain for $d:${normal}"
    show_why $d
  done
fi