Invalid C code generation with `seq[array[...]]`

[tersec]

Nim Version

Any of

Nim Compiler Version 2.2.4 [Linux: amd64]
Compiled at 2026-02-03
Copyright (c) 2006-2025 by Andreas Rumpf

git hash: f7145dd26efeeeb6eeae6fff649db244d81b212d
active boot switches: -d:release

Nim Compiler Version 2.2.6 [Linux: amd64]
Compiled at 2026-02-03
Copyright (c) 2006-2025 by Andreas Rumpf

git hash: ab00c56904e3126ad826bb520d243513a139436a
active boot switches: -d:release

Nim Compiler Version 2.2.7 [Linux: amd64]
Compiled at 2026-02-03
Copyright (c) 2006-2026 by Andreas Rumpf

git hash: d48fc130c137f22d2e9d3c35eba215ed7684f186
active boot switches: -d:release

Nim Compiler Version 2.3.1 [Linux: amd64]
Compiled at 2026-02-03
Copyright (c) 2006-2026 by Andreas Rumpf

git hash: bfc27867187e28dd3b5f2a887450cfc2c465da98
active boot switches: -d:release

with either of

gcc (Debian 15.2.0-12) 15.2.0
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

or

Debian clang version 21.1.8 (2)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-21/bin

Description

type N = object
  b: seq[array[1'u, int]]
discard N(b: @[[0]])

Admittedly, it's not clear this should compile: one array has size 1'u while the other has size 1. But a C compilation error shouldn't happen regardless. It's also notable that many variations of this code do seem to treat array[1, int] and array[1'u, int] as at least implicitly convertible types.

Current Output

Hint: used config file '/tmp/nim23/config/nim.cfg' [Conf]
Hint: used config file '/tmp/nim23/config/config.nims' [Conf]
......................................................................
CC: system/exceptions.nim
CC: std/private/digitsutils.nim
CC: system/dollars.nim
CC: system.nim
CC: u.nim
/tmp/tmp.pgKbRZ2xbT/@mu.nim.c: In function ‘NimMainModule’:
/tmp/tmp.pgKbRZ2xbT/@mu.nim.c:143:9: error: incompatible types when assigning to type ‘tySequence__PaPqxATneMvaJgZdR29cujw’ from type ‘tySequence__iR7FNQIicfV9cQXx6NvdXYw’
  143 | T1_.b = colontmpD_;
      |         ^~~~~~~~~~
Error: execution of an external compiler program 'gcc -c  -w -fmax-errors=3 -fno-strict-aliasing -pthread   -I/tmp/nim23/lib -I/tmp -o /tmp/tmp.pgKbRZ2xbT/@mu.nim.c.o /tmp/tmp.pgKbRZ2xbT/@mu.nim.c' failed with exit code: 1

Expected Output

No C compilation error

Known Workarounds

No response

Additional Information

No response

[ringabout]

Another failed example with codegen errors:

var x: array[5..6, int] = [0, 1]
var y: array[1..2, int] = [0, 3]

# echo x == y # compiles
echo @[x] == @[y]

The hash type of array types should perhaps concern the length of index instead of types