[BUG] StringLiteral concat works only in narrow cases

[akirchhoff-modular]

Reported by @dom96 on Discord.

1. String literals do not persist across cells:

   Cell 1: var x = "hello".
   Cell 2: print(x)

   Expected result: "hello" printed
   Actual result: Blank line printed

2. Concatenation with a string literal stored in a variable causes an error

   var x = "Hello"
   print(x)
   print("hi" + x)

   Expected result: "hihello" printed
   Actual result: Error: failed to legalize operation 'pop.string.concat' that was explicitly marked illegal

[Mogball]

We need to autopromote string literals to the String type, which properly supports runtime concatenation.

[Mogball]

Closing in favour of #100

[akirchhoff-modular]

@Mogball Is #100 sufficient to capture this? For example, it seems like let x: StringLiteral = "hello" and print(x) in separate cells should work, and would also have explicitly turned off auto-promotion so #100 would not be relevant. Am I missing something?

[Mogball]

Yes. StringLiteral.add would have to promote to a String

[akirchhoff-modular]

I'm not talking about __add__, I'm talking just about having a StringLiteral variable in one cell and printing it in another. This is bullet point 1 in this issue -- I understand bullet point 2 is separate.

[Mogball]

Ah I see. That will probably not work in the notebook environment because string literals are pointers to static memory, which only lives as long as the jit'd object (I think). I'll file a new issue appropriately.

[akirchhoff-modular]

Sounds good. If you could, please link the new issue if you file it publicly (or send me the issue privately otherwise, please).

[Mogball]

#232