Modification via a ref isn't detected with {.experimental: "strictFuncs".} with default GC

[sschwarzer]

A modification of a recursive structure via a ref isn't detected by the compiler.

Example

{.experimental: "strictFuncs".}
type
  XmlNode = ref object
    s: seq[XmlNode]

func processNode(node: XmlNode) =
  node.s.delete(0)

let node = XmlNode(s: @[XmlNode()])
node.processNode()

(Thanks to @Yardanico for reducing my code example further. :-) )

Current Output

Hint: used config file '/.../.choosenim/toolchains/nim-#devel/config/nim.cfg' [Conf]
Hint: used config file '/.../.choosenim/toolchains/nim-#devel/config/config.nims' [Conf]
Hint: used config file '/.../config.nims' [Conf]                                
....                                                                            
Hint:  [Link]                                                                   
Hint: 30952 lines; 0.166s; 31.805MiB peakmem; Debug build; proj: /.../strict_funcs_test.nim; out: /.../strict_funcs_test [SuccessX]

Expected Output

The modification is detected with --gc:orc.

Hint: used config file '/.../.choosenim/toolchains/nim-#devel/config/nim.cfg' [Conf]
Hint: used config file '/.../.choosenim/toolchains/nim-#devel/config/config.nims' [Conf]
Hint: used config file '/.../config.nims' [Conf]                                
.....                                                                           
/../strict_funcs_test.nim(7, 9) template/generic instantiation of `delete` from here
/../.choosenim/toolchains/nim-#devel/lib/system.nim(1268, 16) template/generic instantiation of `defaultImpl` from here
/../.choosenim/toolchains/nim-#devel/lib/system.nim(1231, 13) template/generic instantiation of `move` from here
/../.choosenim/toolchains/nim-#devel/lib/system.nim(259, 10) template/generic instantiation of `setLen` from here
/../.choosenim/toolchains/nim-#devel/lib/system/seqs_v2.nim(112, 6) Error: 'setLen' can have side effects
an object reachable from 'newlen' is potentially mutated                        
/../.choosenim/toolchains/nim-#devel/lib/system/seqs_v2.nim(121, 11) the mutation is here
/../.choosenim/toolchains/nim-#devel/lib/system/seqs_v2.nim(122, 9) is the statement that connected the mutation to the parameter

Additional Information

$ nim -v
Nim Compiler Version 1.3.5 [Linux: amd64]
Compiled at 2020-07-26
Copyright (c) 2006-2020 by Andreas Rumpf

active boot switches: -d:release

[Araq]

The problem here is that you enable the strict checking for your own code and not for delete.

[bung87]

with default GC nimSeqsV2 not enabled , it will not call setLen in seqs_v2.nim which declared as {.noSideEffect.}

[sschwarzer]

The problem here is that you enable the strict checking for your own code and not for delete.

Thank you.

Does that mean I should get the compiler error for

$ nim c --experimental:strictFuncs strictfuncs_test.nim

? I don't. :)

And according to what you said, --gc:orc shouldn't have given me an error either, if I understood correctly. :)