glitch with anon vars causes incorrect `Cannot assign to an immutable value` error

[p6rt]

Migrated from rt.perl.org#130855 (status was 'resolved')

Searchable as RT130855$

[p6rt]

From @zoffixznet

Expected no errors, but in the first case it complains about assignment to immutable value even though none exist in the code.

  zoffix@​VirtualBox​:~$ perl6 -e 'm​: sub foo () {$ = 42}; for ^2000000 { $ = foo }; say now - INIT now'
  Cannot assign to an immutable value
  in block <unit> at -e line 1

  zoffix@​VirtualBox​:~$ MVM_SPESH_DISABLE=1 perl6 -e 'm​: sub foo () {$ = 42}; for ^2000000 { $ = foo }; say now - INIT now'
  2.6287172
  zoffix@​VirtualBox​:~$ perl6 --optimize=off -e 'm​: sub foo () {$ = 42}; for ^2000000 { $ = foo }; say now - INIT now'
  1.3881109
  zoffix@​VirtualBox​:~$ perl6 -e 'm​: sub foo () {$ = 42}; for ^2 { $ = foo }; say now - INIT now'
  0.00196070
  zoffix@​VirtualBox​:~$

[p6rt]

From @jnthn

On Fri, 24 Feb 2017 15​:02​:23 -0800, cpan@​zoffix.com wrote​:

Expected no errors, but in the first case it complains about
assignment to immutable value even though none exist in the code.

zoffix@​VirtualBox​:~$ perl6 -e 'm​: sub foo () {$ = 42}; for ^2000000 {
$ = foo }; say now - INIT now'
Cannot assign to an immutable value
in block <unit> at -e line 1

Was fixed in spesh work last month or so; test now added to S04-declarations/state.t so we don't regress.

[p6rt]

The RT System itself - Status changed from 'new' to 'open'

[p6rt]

@jnthn - Status changed from 'open' to 'resolved'