--gc:arc SIGSEGV with ptr aliasing

[timotheecour]

--gc:arc gives SIGSEGV in snippet below; it works without --gc:arc

Example

when true:
  var x = "abc"
  let y: ptr char = addr x[0]
  echo y[]
  y[] = 'A'
  echo x

Current Output

a
Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0919.nim(118) t0919
SIGBUS: Illegal storage access. (Attempt to read from nil?)

Expected Output

a
Abc

Additional Information

• recent devel a33b72a
• maybe related to --gc:arc SIGSEGV, while --gc:refc works fine. #13133 (no idea though because code snippet in that issue is quite large)

[Araq]

I'm afraid this cannot be supported with the new string implementation. You have to call ensureNoLiteral(x) first, an API we don't have yet (?)

The implementation for this is in nimPrepareStrMutationV2.

[cooldome]

Closed as won't fix

[timotheecour]

I think closing is premature; there are things that can be done to at least improve things here