Allow disabling autocompletion with IRB_USE_AUTOCOMPLETE=false

[st0012]

Currently, the only 2 ways to disable autocompletion are:

1. Create .irbrc and set IRB.conf[:USE_AUTOCOMPLETE] = false
2. Add the --noautocomplete flag when using the irb executable

Both of them are less convenient than setting a env var and are lesser known to devs.

And given the number of problems the autocompletion has (see #445), I think we should allow disabling it with a simple IRB_USE_AUTOCOMPLETE=false.

[st0012]

cc @k0kubun

[k0kubun]

Both of them are less convenient than setting a env var and are

It depends. ~/.irbrc is scoped to IRB, and --noautocomplete is scoped to each IRB invocation. Having USE_AUTOCOMPLETE in your shell could impact any other non-IRB program. Global variables are "convenient" but it doesn't necessarily mean it improves maintainability. I would still use ~/.irbrc even after this is merged.

I like that you chose a name consistent with irbrc, but when it comes to environment variables, I would choose a name that includes IRB to avoid possible namespace conflicts.

lesser known to devs.

How will it be easier to know of this environment variable than .irbrc or --noautocomplete?

And given the number of problems the autocompletion has (see #445), I think we should allow disabling it with a simple USE_AUTOCOMPLETE=false.

If it's that problematic, we might want to consider disabling it by default until all the issues are addressed. The most annoying part of auto-completion for me is the fact that the prompt position randomly moves depending on the completion size when you're at the bottom of the window, but currently nobody even discusses it maybe because there are more annoying problems for other people.

I appreciate that reline-powered IRB supports multi-line editing and can be used like an editor, but I still use one-liner inputs on IRB most of the time. It's never easier to edit a multi-line long script on reline than your own actual editor. If you mostly use a one-liner, it feels more like a normal REPL than an editor. It's normal to have auto-completion on an editor, but not on a REPL. While it might be useful for some people to have this capability, I don't think this needs to be enabled by default, especially when it's a factor that annoys IRB users.

[st0012]

I like that you chose a name consistent with irbrc, but when it comes to environment variables, I would choose a name that includes IRB to avoid possible namespace conflicts.

We can use the same prefix convention debug uses, which would be RUBY_IRB_USE_AUTOCOMPLETE.

How will it be easier to know of this environment variable than .irbrc or --noautocomplete?

I think I should phrase it differently: in my experience, env var is a common way to control features like this (such as NO_COLOR, which IRB also supports). So if given no guidance on how to configure the feature, I'd look for related env vars first.

If it's that problematic, we might want to consider disabling it by default until all the issues are addressed.

I thought about it before. But based on my polling result in #445, we have around 28% of users satisfied with it as it is today. And only 17% of them dislike it enough to disable it. So if we disable it now, it'd be a breaking change for the 28% of users, which is a big number.

Therefore, I think we should keep it enabled, but also make it easier to disable. That's why I want to propose this env var.

[k0kubun]

Fair enough.

We can use the same prefix convention debug uses, which would be RUBY_IRB_USE_AUTOCOMPLETE.

It makes sense that debug.gem needs to start it with RUBY_ because "debug" is not unique to Ruby, but for IRB, I guess it's fine to just use IRB_ since RB is Ruby and fairly unlikely to conflict on a shell, especially when you were okay with prefixing nothing. FYI Bundler uses BUNDLE_GEMFILE and BUNDLE_JOBS. WDYT about calling it IRB_USE_AUTOCOMPLETE?

[st0012]

IRB_USE_AUTOCOMPLETE sounds good, updated 👍