No longer require hooks/extensions must be added to overlays

[lrascao]

This is a breaking change in the relx configuration section, the change is small and i think the gain outweighs the hassle.

No longer demand that developers add a hook/extension and also
correctly configure the required overlay copy instructions as this
now gets automatically added. Start script extensions now also
support descriptions.

Extensions:
previous:

        {extended_start_script_extensions, [
            {bar, "extensions/bar"},
            {foo, "extensions/foo"},
            {baz, "extensions/baz"}]},
        {overlay, [
            {copy, "./bar", "bin/extensions/bar"},
            {copy, "./foo", "bin/extensions/foo"},
            {copy, "./baz", "bin/extensions/baz"}]}

after:

        {extended_start_script_extensions, [
            % auto copied over to `bin/extensions/bar` with empty description
            {bar, "./bar"},
            % auto copied over to `bin/extensions/foo` with description `"foo description"`
            {foo, "./foo", "foo description"},
            % auto copied over to `bin/extensions/baz` with description `"baz description"`
            {baz, "./baz", "bin/extensions/baz", "baz description"}
        ]}

Hooks:
previous:

        {extended_start_script_hooks, [
            {pre_start, [
                {custom, "hooks/pre_start"}
            ]},
            {post_start, [
                wait_for_vm_start,
                {pid, "foo.pid"},
                wait_for_vm_start,
                {custom, "hooks/post_start"}
            ]},
            {pre_stop, [
                {custom, "hooks/pre_stop"}
            ]},
            {post_stop, [
                {custom, "hooks/post_stop"}
            ]},
            {status, [
                {custom, "hooks/status"}
            ]}
        ]},
        {overlay, [
            {copy, "./hooks/status", "bin/hooks/status"},
            {copy, "./hooks/{pre,post}_{start,stop}", "bin/hooks/"}
        ]}

after:

        {extended_start_script_hooks, [
            {pre_start, [
                % auto copied over to `bin/hooks/pre_start`
                {custom, "hooks/pre_start"}
            ]},
            {post_start, [
                wait_for_vm_start,
                {pid, "foo.pid"},
                wait_for_vm_start,
                {custom, "hooks/post_start"},
                % auto copied over to `bin/hooks/extra/post_start`
                {custom, "hooks/post_start2", "bin/hooks/extra/post_start"}
            ]},
            {pre_stop, [
                {custom, "hooks/pre_stop"}
            ]},
            {post_stop, [
                {custom, "hooks/post_stop"}
            ]},
            {status, [
                {custom, "hooks/status"}
            ]}
        ]}

[lrascao]

@Vagabond kindly offered to help out here with his shell-fu

[ferd]

Does this change break anything? Will people's old scripts stop working? If not, we should keep the old format for shelltests. If it breaks, we gotta figure out a release strategy for that

[lrascao]

It does break extension scripts, previously you said:
{name, <where the start script can find the extension>}
and now:
{name, <extension script location>}

I think the breakage is worth it as it:

• makes it clearer and easier for people using extension scripts
• is a simple change
• possibility of adding descriptions to the usage

To ease the migration we can error out when unable to find the source script, update the doc and link it in the error

[ferd]

Maybe. The thing is I have a hard time with breakage since we just went to 4.0.0, and now we'd bump to 5.0.0 right away. I get it's worth it, but it's forcing more breakage into how everyone is building releases. Would it make sense to name the options extended_start_script_extensions_src and extended_start_script_hooks_src where the distinction is that the *_src version assumes you want the source path bundled in the proper place? Would the burden be too crappy to deal with there?

I'm hoping to avoid the case where someone had all their releases broken when upgrading the last rebar3 point version, and gets to break them all over again on the next point version, but maybe this is too narrow of a concern and not that many people use extensions anyway?

[lrascao]

but maybe this is too narrow of a concern and not that many people use extensions anyway?

yeah, that's what i'm thinking, the few people that do use them will probably be ok and won't mind the change as it makes using them generally easier.
cc @Vagabond @uwiger, yours are the only projects that i know of that make use of extension scripts, what are your thoughts on this?

We can go with the keep retro-compat route, however cruft will pile on and in the long run things will just get harder to reason

[ferd]

Yeah. I mean I'm okay with removing cruft, I think part of the challenge of maintaining this stuff is in how many edge cases we create. I'm fine with forcing the breaking change if typical users are good with it, I'd say, and there aren't too many of them. This might be a good candidate for it.

[lrascao]

There's no big rush with this as it's an improvement over existing functionality, we can wait and see what people have to say

[tsloughter]

Don't think we can have breakage like this. Any way to support both?

[lrascao]

Suppose we can keep the previous rebar.config format and add a new one, something like:

       % old format
       {extended_start_script_extensions, [
            {bar, "extensions/bar"}
       ]},
       {extended_start_script_hooks, [
           {pre_start, [
              {custom, "hooks/pre_start"}
           ]}
       ]},

        % new format
        {extended_start_script, [
           {extensions, [
              % auto copied over to `bin/extensions/baz` with description `"baz description"`
              {baz, "./baz", "bin/extensions/baz", "baz description"}
           ]},
           {hooks, [
               {post_start, [
                             wait_for_vm_start,
                             {pid, "foo.pid"},
                             wait_for_vm_start,
                             {custom, "hooks/post_start"},
                             {custom, "hooks/post_start2", "bin/hooks/extra/post_start"}
               ]}
           ]}
       ]}

[paulo-ferraz-oliveira]

Assuming there's breakage, are the required changes documented somewhere?

[lrascao]

yeah, they're documented here and here, they'd need to be updated though

[paulo-ferraz-oliveira]

@lrascao, the links are broken. They point to https://github.com/erlware/relx/pull/here.

Edit: in any case I'll check rebar3.org, thanks.
Edit 2: ah, I see, but that'd assume that I'd look at the doc.s after the breakage hit me 😄 I guess that's Okay, but the release notes should probably mention it.

[ferd]

Yeah I'd feel better if we just add the new format at some point I guess. Prevents breakage at least.

[lrascao]

roger, i'll keep old tests and expand them with this new format then
@tsloughter good with the proposed format above?

[lrascao]

gonna push forward with this format, hopefully this week i can squeeze this in

[tsloughter]

@lrascao any update? I'm going to make a release soon, this will probably be bumped to the next release unless you are close?

[lrascao]

damn, I forgot all about this, better not block this release

[tsloughter]

Ok, will do.

[tsloughter]

oops, didnt meAn to close, thought github knew to switch the target...

[tsloughter]

Ah, I was supposed to rename the default branch and not switch the default... well this is going to be a pain.