Consider the situation:

• There is a script which, somewhere deep inside, runs dub run
• We would like to substitute that invocation with a provided copy of the package (e.g. because we need to run the script offline, or use a slightly modified version of the package being run)

So, if the script runs dub run [email protected], we should be able to use dub add-local path/to/our/version/of/package 1.2.3 first to make the former command use the version specified in the latter command.

Alternatively, a hypothetical dub install --version=1.2.3 could install the package from the current directory into Dub's cache, so that dub run would then use it.