Nim: Compiler crashes when concatenating a string with `nil`

[tim-st]

The following code crashes without linenumber on Nim Compiler Version 0.18.1 [Windows: amd64]; Compiled at 2018-07-14; git hash: 332469692d5053c6c935163e196b117b6979c8e7

proc test(): string =
  result = nil & ""

with
Error: unhandled exception: false ast.nim(1606) getStrOrChar [AssertionError]

Maybe a better error message is sufficient here.

[stefanos82]

If I'm not mistaken, @Araq changed nil's semantics.

To verify what I'm saying, you can test it with the following code:

import typetraits

proc `$`*(T: typedesc): string = name(T)

template test(x): typed =
  echo "type: ", type(x), ", value: ", x

test nil

You should get the following error message (I'm wrapping it for readability):

tmp.nim(8, 6) Error: ambiguous call; both 
system.$(s: WideCString)[declared in lib/system/widestrs.nim(167, 5)] and 
system.$(x: seq[T])[declared in lib/system.nim(2561, 5)] match for: (nil)

@Araq, by the way is this considered a bug or an expected behavior?

[tim-st]

Yes, it was/will be changed. But this code wasn't a try to concatenate nil with a string, instead I wanted to show a situation where compiler crashes without line number. These crashes without linenumber are very bad and force the developer to search the bug on his own...

[stefanos82]

Ah yes, you are completely right. How come I have missed that? Indeed that's a very unfortunate situation for the user.

[Araq]

Now fails with

Error: type mismatch: got <nil, string>

I know these crashes without line info are bad but they are not caused by a single reason.