Compiler segfaults on simple importcpp in js mode [regression]

[mcclure]

I am using self-built nim from git. I tested the following with 0062077 . The problem appeared only after I upgraded from 07d7d35 (I did not see the problem with 07d7d35 and the same code).

I write this code:

type QCbase* {.importc.} = ref object of RootObj
    num1* {.importc.}: float
    str2* {.importc.}: cstring
proc newQCbase*() : QCbase {.importcpp:"new QCbase".}

let inst1 : QCbase  = newQCbase()

And compile it with nim js -o:testNim2.js testNim2.nim, I get an error:

Hint: used config file 'C:\msys64\home\Andi\work\g\Nim\config\nim.cfg' [Conf]
Hint: system [Processing]
Hint: testnim2 [Processing]
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

I do NOT get the error if I instead use the code:

type QCbase* {.importc.} = ref object of RootObj
    num1* {.importc.}: float
    str2* {.importc.}: cstring
proc newQCbase*() : QCbase {.importcpp:"new QCbase(@)".}

let inst1 : QCbase  = newQCbase()

With the difference being the (@).

I also do not get a segfault if I compile with nim c instead of nim js.

This might be related to the fix for #4496

[mcclure]

Under certain circumstances I find that on repeated invocations, instead of a segfault I get

command line(0, 1) Error: internal error: gen: unknown node type: nkNone
No stack traceback available
To create a stacktrace, rerun compilation with ./koch temp js <file>

I can give you the reproduction steps for this if it is helpful, but I assume this is just a byproduct of the compiler segfault.