feat(compiler): Providing, including, reproviding exceptions

[alex-snezhko]

Closes #1053

Syntax:

// provider.gr
provide exception MyException
// OR
exception MyException
provide { exception MyException }

// includer.gr
include "./provider"
from Provider use { exception MyException }
// can re-provide
provide { exception MyException }

[spotandjake]

Looks good, just had one small nit.

[spotandjake]

For completeness and to follow the rest it would probably make sense to add the test here without as as well to mirror the variable and type import.

Suggested change

	from Opt use { MutableOpt, /* comment1 */ ImmutableOpt /* comment2 */ as /* comment3 */ Imm /* comment4 */, /* comment5 */ type /* comment6 */ Opt, type Opt as /* comment7 */ OptAlias, exception Exc as /* comment8 */ E }
	from Opt use { MutableOpt, /* comment1 */ ImmutableOpt /* comment2 */ as /* comment3 */ Imm /* comment4 */, /* comment5 */ type /* comment6 */ Opt, type Opt as /* comment7 */ OptAlias, , exception /* comment8 */ Exc, exception Exc as /* comment9 */ E }

[ospencer]

Can you add some tests where you provide an exception + a value of that exception and then successfully pattern match on it in the consuming module? Just want to make sure that works.

[peblair]

LGTM modulo @ospencer's test request

[spotandjake]

as exceptions behave a little differently then most types. in that the value is based off the type. so if you did

exception F
print(F) // F

when you use the from syntax with as. you could do

from Module use { exception F as Y }

print(Y) // F

I feel like this might be a little confusing the closest analogy I can think of would be if we allowed enum aliasing, you could do something like print(Enum.North) and get South as the printed value.

I wonder if we want to allow aliasing exceptions.

Cut down version of message sent in discord.

Also we should add a test for throw Module.Exception with the Module. syntax rather than just using the from syntax.

[marcusroberts]

Looks useful to me and good syntax.