only write lock file if locks have changed

[ferd]

Supercedes #2214

[hcs42]

Hi @tsloughter and @ferd,

The vim-erlang-compiler and vim-erlang-omnicomplete projects try to guess whether the project is rebar2 or rebar3 based on the presence of the rebar3.lock file. (Present → rebar3, not present → rebar2.)

This heuristic (which not very robust in any case) stopped working after this PR, since rebar3 compile no longer generates rebar.lock file for projects without dependencies.

Do you have a suggestion for a better way to decide if the current project is rebar2 or rebar3?

[ferd]

This is already fixed in master, next point release should be fine.

[hcs42]

Thanks! For future reference: PR #2353 fixed this.