Interpreter: allow some options, and colorize whereami

[asterite]

This PR allows passing the following options to the interpreter:

• -D FLAG
• --error-trace
• -h
• --no-color

In addition to that, if color is desired, the output of whereami and also the output when you run into debugger is colored.

Before this PR:

With this PR:

With this PR and --no-color (notice that the line numbers are no longer colored):

[beta-ziliani]

Nice, thanks!

[HertzDevil]

Could you also add --prelude and --link-flags?

[asterite]

I initially added prelude, but the interpreter depends on exit and nothing really works without the prelude. For example inspecting values won't work.

Link flags... I think that's a new feature. When will they show up?

I actually intended to add coloring support in this PR. I added some other options that were trivial to implement. Could we maybe leave the other, more colplex ones, for later PRs?

[HertzDevil]

Never mind about --link-flags, I was thinking about Windows but -D is probably enough.

What do you mean by exit?

[asterite]

When you do crystal i and then you quit, the interpreter calls exit manually by creating a Call and then interpreting that:

crystal/src/compiler/crystal/interpreter/repl.cr

Line 34 in 8eb1413

interpret_exit

crystal/src/compiler/crystal/interpreter/repl.cr

Lines 182 to 184 in 8eb1413

	private def interpret_exit
	interpret(Call.new(nil, "exit", global: true))
	end

Without the default prelude, that doesn't work. Well, maybe it will work with some other prelude, but not with the empty one. I guess we could still add the option. After all it's a "use this if you want to, but you probably shouldn't".

Here's how it works right now with --prelude=empty:

➜  crystal git:(feature/interpreter-options-and-colorize) ✗ bin/crystal i --prelude=empty
icr:1:0> 1
=> Error while calling inspect on value: undefined method 'inspect' for Int32
1
icr:2:0> a = 1
=> Error while calling inspect on value: undefined method 'inspect' for Int32
1
icr:3:0> Showing last frame. Use --error-trace for full trace.

Error: undefined local variable or method 'exit' for top-level

Not a very pleasant experience :-)

Here's interpreting a file that only does a = 1:

Showing last frame. Use --error-trace for full trace.

Error: undefined local variable or method 'exit' for top-level

Again, not very useful.

But I guess it doesn't hurt either to add that option to be able to experiment with other preludes.

[straight-shoota]

it doesn't hurt either to add that option to be able to experiment with other preludes.

Yes, I agree on that. Choosing a non-standard prelude is an option which is only useful when you know what you're doing. Even with compiled crystal. I think it makes sense to allow it on the interpreter as well.

We could easily improve the error messages or fall back to not calling methods that don't exist. (that's low priority though)

[asterite]

Will this make it to 1.5.0?

[straight-shoota]

Sure. It only affects the interpreter.