Nim Version
nim -v
Nim Compiler Version 2.3.1 [Linux: amd64]
Compiled at 2026-07-16
Copyright (c) 2006-2026 by Andreas Rumpf
git hash: a6fa322
active boot switches: -d:release
Description
As of Nim 2.4.0 RC1 it seems that the 'extern' keyword is no longer emitted for variables imported from another module which have the codegenDecl pragma applied to them.
Example:
# foo.nim
var myvar* {.codegenDecl: "__attribute__ ((aligned (16))) $# $#".}: int = 123# main.nim
import ./foo
echo myvar
Current Output
/usr/bin/ld: /home/exelotl/.cache/nim/main_d/@mmain.nim.c.o:(.bss+0x0): multiple definition of `myvar_u0__foo'; /home/exelotl/.cache/nim/main_d/@mfoo.nim.c.o:(.bss+0x0): first defined here
collect2: error: ld returned 1 exit status
Error: execution of an external program failed: 'gcc -o /home/exelotl/Dev/nim-tests/2026-07-16_19.09/main /home/exelotl/.cache/nim/main_d/@psystem@sexceptions.nim.c.o /home/exelotl/.cache/nim/main_d/@pstd@sprivate@sdigitsutils.nim.c.o /home/exelotl/.cache/nim/main_d/@psystem@sdollars.nim.c.o /home/exelotl/.cache/nim/main_d/@psystem.nim.c.o /home/exelotl/.cache/nim/main_d/@mfoo.nim.c.o /home/exelotl/.cache/nim/main_d/@mmain.nim.c.o -pthread -pthread -ldl'
Expected Output
Known Workarounds
No response
Additional Information
Previously in the generated C code for main.nim, myvar would be declared as such:
But now it is declared as:
__attribute__ ((aligned (16))) NI myvar_u0__foo = ((NI) 123);
which is the same as its definition in the generated C code for foo.nim, leading to multiple definition errors.
This issue also occurs if you don't use the variable directly but call an inline function that uses it.
It doesn't occur in the last stable release (2.2.10).
It only seems to happen for variables, i.e. codegenDecl procs are still working fine.
Nim Version
nim -v
Nim Compiler Version 2.3.1 [Linux: amd64]
Compiled at 2026-07-16
Copyright (c) 2006-2026 by Andreas Rumpf
git hash: a6fa322
active boot switches: -d:release
Description
As of Nim 2.4.0 RC1 it seems that the 'extern' keyword is no longer emitted for variables imported from another module which have the codegenDecl pragma applied to them.
Example:
Current Output
Expected Output
Known Workarounds
No response
Additional Information
Previously in the generated C code for main.nim, myvar would be declared as such:
But now it is declared as:
which is the same as its definition in the generated C code for foo.nim, leading to multiple definition errors.
This issue also occurs if you don't use the variable directly but call an inline function that uses it.
It doesn't occur in the last stable release (2.2.10).
It only seems to happen for variables, i.e. codegenDecl procs are still working fine.