VM issue with globals and assignments

[nitely]

Nim Version

Nim Compiler Version 2.3.1 [Linux: amd64]
Compiled at 2025-09-25
Copyright (c) 2006-2025 by Andreas Rumpf

git hash: 9f74712
active boot switches: -d:release

Description

Nim 1.6.20 works as expected; the regression is present in Nim +2.0

type Conf = object
  val: int

const defaultConf = Conf(val: 123)

template foo(conf) =
  echo conf.val
  var conf2 = conf
  echo conf2.val

static:
  var conf = defaultConf
  conf = defaultConf  # removing this results in the expected output
  conf.val = 2
  foo(defaultConf)

Current Output

123
2

Expected Output

123
123

Known Workarounds

wrap the static body in a proc.

Additional Information

No response

[ringabout]

!nim c

type Conf = object
  val: int

const defaultConf = Conf(val: 123)

template foo(conf) =
  assert conf.val == 123
  var conf2 = conf
  assert conf2.val == 123

static:
  var conf: Conf = defaultConf
  conf = defaultConf  # removing this results in the expected output
  conf.val = 2
  foo(defaultConf)

[github-actions]

🐧 Linux bisect by @ringabout (member)

devel 👎 FAIL

Output

Filesize 0 (0 bytes)
Duration

stable 👎 FAIL

Output

Filesize 0 (0 bytes)
Duration

2.2.2 👎 FAIL

Output

Filesize 0 (0 bytes)
Duration

2.0.0 👎 FAIL

Output

Filesize 0 (0 bytes)
Duration

1.6.20 👍 OK

Output

Filesize 95.50 Kb (97,792 bytes)
Duration 1 mins

1.4.8 👍 OK

Output

Filesize 91.16 Kb (93,344 bytes)
Duration

1.2.18 👍 OK

Output

Filesize 86.88 Kb (88,968 bytes)
Duration

1.0.10 👍 OK

Output

Filesize 81.98 Kb (83,952 bytes)
Duration

#b5f64f55d ➡️ 🐛

Diagnostics

ringabout introduced a bug at 2023-02-01 02:22:10 +0800 on commit #b5f64f55d with message:

The bug is in the files:

The bug can be in the commits:

• #43b1b9d07
• #900fe8f50
• #ff8ab0672
• #cbf3ed9d9
• #b5f64f55d
• #ebaa07b95

(Diagnostics sometimes off-by-one).

Stats

• GCC 13.3.0
• Clang 18.1.3
• NodeJS 19.5
• Created 2025-10-07T12:24:12Z
• Comments 1
• Commands nim c --run -d:nimDebug -d:nimDebugDlOpen -d:ssl -d:nimDisableCertificateValidation --forceBuild:on --colors:off --verbosity:0 --hints:off --lineTrace:off --nimcache:/home/runner/work/Nim/Nim --out:/home/runner/work/Nim/Nim/temp /home/runner/work/Nim/Nim/temp.nim

🤖 Bug found in 15 mins bisecting 2998 commits at 195 commits per second

[ringabout]

Not related to templates