Fail loudly on error when executing a cmd in an app.src vsn

[aronisstav]

This PR fixes a bug.

Description
When running rebar3 compile on a strange environment (Windows...), a cmd command in a vsn attribute in an .app.src file failed.

Expected behaviour
An error is prominently displayed.

Actual behaviour
The error was only available with DEBUG=1 and localizing it to the vsn attribute took quite some further digging.

Additional info
While at it, make it so that {abort_on_error, Msg} ALSO shows the error that generated it, indiscriminately. This is a little breaking, but should be a good thing.

I think that this PR is good enough as-is. I might have time to also add a test, if someone kindly points out specifically where.

[ferd]

Can you show the expected difference between the old output and the new one? I'm having a bit of a hard time just tracing in my mind what the difference in output is expected to look like.

[ferd]

if the error message takes place this deep, then it would make sense not to make assumptions on what the caller was doing ("was it really called in a .app.src file?") and simply report the error at its own level (something like "Command x failed") to prevent misguiding error messages when the callsites are expanded.

If we want to provide contextual errors with high-level concerns, then we would need to put in a conditional here and return {ok, VsnString} | {error, Term} and move the reporting to the parent.

[aronisstav]

Can you clarify a little bit? I am guessing you mean that this code could be reached in different ways, but my understanding, without really checking, is that the only way to reach cmd_vsn_invoke/2 is when really evaluating a cmd in a vsn property, in an .app.src file, which is what my error message reports.

[ferd]

Yeah this is more of future-proofing. I.e. the function cmd_vsn_invoke knows it is about a version, but has no idea it actually comes from a .app.src file.

[aronisstav]

Can you show the expected difference between the old output and the new one? I'm having a bit of a hard time just tracing in my mind what the difference in output is expected to look like.

Right, I forgot!

Before:

❯ cat src/foo.app.src                    
{application, foo,
 [{description, "An OTP application"},
  {vsn, {cmd, "false"}},
  {registered, []},
  {mod, {foo_app, []}},
  {applications,
   [kernel,
    stdlib
   ]},
  {env,[]},
  {modules, []},

  {licenses, ["Apache 2.0"]},
  {links, []}
 ]}.


❯ rebar3 compile                                   
===> Verifying dependencies...
===> Analyzing applications...
===> Compiling foo

❯ echo $?                                             
1

❯ DEBUG=1 rebar3 compile                                 
===> Expanded command sequence to be run: [app_discovery,install_deps,lock,compile]
===> Running provider: app_discovery
===> Found top-level apps: [foo]
	using config: [{src_dirs,["src"]},{lib_dirs,["apps/*","lib/*","."]}]
===> Running provider: install_deps
===> Verifying dependencies...
===> Running provider: lock
===> Running provider: compile
===> Compile (apps)
===> Running hooks for compile with configuration:
===> 	{pre_hooks, []}.
===> Compile (project_apps)
===> Running hooks for compile in app foo (/Users/stavros/sandbox/foo) with configuration:
===> 	{pre_hooks, []}.
===> Running hooks for erlc_compile in app foo (/Users/stavros/sandbox/foo) with configuration:
===> 	{pre_hooks, []}.
===> Analyzing applications...
===> Compiling foo
===> compile options: {erl_opts, [debug_info]}.
===> files to analyze ["/Users/stavros/sandbox/foo/src/foo_sup.erl",
                              "/Users/stavros/sandbox/foo/src/foo_app.erl"]
===> Running hooks for erlc_compile in app foo (/Users/stavros/sandbox/foo) with configuration:
===> 	{post_hooks, []}.
===> Running hooks for app_compile in app foo (/Users/stavros/sandbox/foo) with configuration:
===> 	{pre_hooks, []}.
===> sh(false)
failed with return code 1 and the following output:

After:

❯ rebar3 compile                           
===> Verifying dependencies...
===> Analyzing applications...
===> Compiling foo
===> vsn cmd in .app.src failed
sh(false)
failed with return code 1 and the following output:

[TheGeorge]

It would be good to add the actual filename or path here as well. Otherwise, if you have many apps its up to the user to find the one with the bad vsn command