Add --eval option to shell

[choptastic]

Hey folks,

I'm not sure if there's an equivalent function in rebar3 or not, but I found a need to sort-of re-implement erl -eval but for the rebar3 shell command, so rebar3 shell --eval "my_module:my_function()".

This implementation also works like erl -eval in that it supports multiple --eval arguments.

Thoughts?

[ferd]

Looks workable. What's the expected behaviour when someone submits gibberish? Is it different or inline with what -eval does in the shell?

[choptastic]

Hey @ferd, good question. At this point, my expected behavior was "crash with whatever error message it happens to produce."

Which, right now, looks like this:

==> Evaluating: "sdfg()"
===> Uncaught error in rebar_core. Run with DIAGNOSTIC=1 to see stacktrace or consult rebar3.crashdump
===> When submitting a bug report, please include the output of `rebar3 report "your command"`

with DIAGNOSTIC=1 on, it looks like this:

===> Found shell evals from command line option.
===> Evaluating: "sdfg()"
===> Uncaught error in rebar_core. Run with DIAGNOSTIC=1 to see stacktrace or consult rebar3.crashdump
===> Uncaught error: {badmatch,
                                {error,
                                    {1,erl_parse,
                                     ["syntax error before: ",[]]}}}
===> Stack trace to the error location:
[{rebar_prv_shell,eval,1,
                  [{file,"/home/gumm/code/rebar3/src/rebar_prv_shell.erl"},
                   {line,357}]},
 {lists,map,2,[{file,"lists.erl"},{line,1315}]},
 {rebar_prv_shell,shell,1,
                  [{file,"/home/gumm/code/rebar3/src/rebar_prv_shell.erl"},
                   {line,135}]},
 {rebar_core,do,2,
             [{file,"/home/gumm/code/rebar3/src/rebar_core.erl"},{line,155}]},
 {rebar3,run_aux,2,
         [{file,"/home/gumm/code/rebar3/src/rebar3.erl"},{line,193}]},
 {rebar3,main,1,[{file,"/home/gumm/code/rebar3/src/rebar3.erl"},{line,66}]},
 {escript,run,2,[{file,"escript.erl"},{line,750}]},
 {escript,start,1,[{file,"escript.erl"},{line,277}]}]

Which could be made more straigthtforward.

If you'd like, I can make these changes sometime in about 2 weeks (traveling for the next few weeks, so won't be doing much by way of this kind of stuff).

Whadya think?

[ferd]

Cleaner error descriptions there would be worth it just to reduce error reports and point towards the issue being in the script being evaluated. It's fine to wait on my end. I'm on vacation as well and doing little OSS.

[choptastic]

Rock on!

[choptastic]

I've updated it to give some better error messages so the user clearly knows it's the --eval switch that's crashing and why it's crashing:

bad syntax error:

$ ./rebar3 shell --eval "io:f)."
...
Eshell V13.0.1  (abort with ^G)
1> ===> Evaluating: "io:f)."
===> Failed to parse -eval expression: "io:f).". Error message: syntax error before: ')'

Valid syntax but the call fails for some reason

./rebar3 shell --eval "no_function()."
...
Eshell V13.0.1  (abort with ^G)
1> ===> Evaluating: "no_function()."
===l> Failed to evaluate expression: "no_function().". Error: error:undef. Run with DIAGNOSTIC=1 to stacktrace or consult rebar3.crashdump

The above, but with DIAGNOSTIC=1:

Eshell V13.0.1  (abort with ^G)
1> ===> No script_file specified.
===> Found shell evals from command line option.
===> Evaluating: "no_function()."
===> --eval failure details: error:undef
Stacktrace: [{erl_eval,no_function,0,[]},
             {erl_eval,local_func,8,[{file,"erl_eval.erl"},{line,660}]},
             {rebar_prv_shell,eval,1,
                              [{file,"/home/gumm/code/rebar3/src/rebar_prv_shell.erl"},
                               {line,366}]},
             {lists,map,2,[{file,"lists.erl"},{line,1315}]},
             {rebar_prv_shell,shell,1,
                              [{file,"/home/gumm/code/rebar3/src/rebar_prv_shell.erl"},
                               {line,140}]},
             {rebar_core,do,2,
                         [{file,"/home/gumm/code/rebar3/src/rebar_core.erl"},
                          {line,155}]},
             {rebar3,run_aux,2,
                     [{file,"/home/gumm/code/rebar3/src/rebar3.erl"},
                      {line,193}]},
             {rebar3,main,1,
                     [{file,"/home/gumm/code/rebar3/src/rebar3.erl"},
                      {line,66}]}]
===> Failed to evaluate expression: "no_function().". Error: error:undef. Run with DIAGNOSTIC=1 to stacktrace or consult rebar3.crashdump

No rush on this - enjoy your vacation!

[choptastic]

Thanks for merging!