Generic type alias for a union type causes gcc error

[emiljanQ3]

Nim Version

Nim Compiler Version 2.2.0 [Windows: amd64]

Description

I'm trying to do a simple union type in nim as such:

type SeqLike[T] = ptr UncheckedArray[T] | seq[T]

proc getFirst[T](list: SeqLike[T]): T =
    list[0]

proc main() =
    let test1 = @[1, 2, 3, 4, 5]
    let test2 = @['1', '2', '3', '4', '5']
    let test3 = cast[ptr UncheckedArray[int]]( addr(test1[0]) )
    let test4 = cast[ptr UncheckedArray[char]]( addr(test2[0]) )

    echo "test1"
    echo getFirst(test1)    
    echo "test2"
    echo getFirst(test2)    
    echo "test3"
    echo getFirst(test3)  
    echo "test4"
    echo getFirst(test4)

if isMainModule:
    main()

Am I doing something wrong here? Either way the nim compiler should catch it before the c-compiler does right? Do you know of any workarounds?

Current Output

CC: [redacted]/Nim/nim-2.2.0/lib/system.nim
CC: test.nim
C:\[redacted]\nimcache\test_d\@mtest.nim.c: In function 'main__test_u7':
C:\[redacted]\nimcache\test_d\@mtest.nim.c:206:34: error: incompatible type for argument 1 of 'getFirst__test_u20'
  206 |         T7_ = getFirst__test_u20(test3);
      |                                  ^~~~~
      |                                  |
      |                                  NI * {aka long long int *}
C:\[redacted]\nimcache\test_d\@mtest.nim.c:120:84: note: expected 'tySequence__qwqHTkRvwhrRyENtudHQ7g' but argument is of type 'NI *' {aka 'long long int *'}
  120 | N_LIB_PRIVATE N_NIMCALL(NI, getFirst__test_u20)(tySequence__qwqHTkRvwhrRyENtudHQ7g list_p0) {
      |                                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:\[redacted]\nimcache\test_d\@mtest.nim.c:214:34: error: incompatible type for argument 1 of 'getFirst__test_u24'
  214 |         T9_ = getFirst__test_u24(test4);
      |                                  ^~~~~
      |                                  |
      |                                  NIM_CHAR * {aka char *}
C:\[redacted]\nimcache\test_d\@mtest.nim.c:130:91: note: expected 'tySequence__lBgZ7a89beZGYPl8PiANMTA' but argument is of type 'NIM_CHAR *' {aka 'char *'}
  130 | N_LIB_PRIVATE N_NIMCALL(NIM_CHAR, getFirst__test_u24)(tySequence__lBgZ7a89beZGYPl8PiANMTA list_p0) {
      |                                                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
Error: execution of an external compiler program 'C:\[redacted]\Nim\nim-2.2.0\dist\mingw64\bin\gcc.exe -c  -w -fmax-errors=3 -mno-ms-bitfields   -IC:\[redacted]\Nim\nim-2.2.0\lib -Ic:\[redacted] -o C:\[redacted]\nimcache\test_d\@mtest.nim.c.o C:\[redacted]\nimcache\test_d\@mtest.nim.c' failed with exit code: 1

Expected Output

Code compiles or nim compiler catches error.

Known Workarounds

No response

Additional Information

No response