Crash if `hostname` is used as a loop variable

[acdha]

I noticed an odd crash while running a command in a loop when I picked a loop variable which matched a variable name:

cadams@tethys ~> for hostname in (cat ~/Projects/…/django-hosts); curl --fail "http://$hostname/server-status?auto"; end
<E> fish: /tmp/fish-20181228-21895-1ih942f/fish-3.0.0/src/parse_execution.cpp:408: failed assertion: retval == ENV_OK && "for loop variable should have been successfully set"
<E> fish: Backtrace:
<E> fish: 0   parse_execution_context_t::run_for_statement(tnode_t<grammar::for_header>, tnode_t<grammar::job_list>) + 902
<E> fish: 1   parse_execution_context_t::run_block_statement(tnode_t<grammar::block_statement>, block_t const*) + 98
<E> fish: 2   parse_execution_context_t::run_1_job(tnode_t<grammar::job>, block_t const*) + 618
<E> fish: 3   parse_execution_context_t::run_job_conjunction(tnode_t<grammar::job_conjunction>, block_t const*) + 128
<E> fish: 4   parse_execution_result_t parse_execution_context_t::run_job_list<grammar::job_list>(tnode_t<grammar::job_list>, block_t const*) + 107
<E> fish: 5   parse_execution_context_t::eval_node(tnode_t<grammar::job_list>, block_t const*, io_chain_t const&) + 187
<E> fish: 6   int parser_t::eval_node<grammar::job_list>(std::__1::shared_ptr<parsed_source_t const>, tnode_t<grammar::job_list>, io_chain_t const&, block_type_t, std::__1::shared_ptr<job_t>) + 231
<E> fish: 7   parser_t::eval(std::__1::shared_ptr<parsed_source_t const>, io_chain_t const&, block_type_t) + 137
<E> fish: 8   parser_t::eval(std::__1::basic_string<wchar_t, std::__1::char_traits<wchar_t>, std::__1::allocator<wchar_t> >, io_chain_t const&, block_type_t) + 162
<E> fish: 9   reader_run_command(parser_t&, std::__1::basic_string<wchar_t, std::__1::char_traits<wchar_t>, std::__1::allocator<wchar_t> > const&) + 419
<E> fish: 10  reader_read(int, io_chain_t const&) + 1376
<E> fish: 11  main + 4946
<E> fish: 12  start + 1

[Process completed]

This reproduces with other shell built-ins (e.g. umask or history).

Versions:

cadams@tethys ~> fish --version
fish, version 3.0.0
cadams@tethys ~> brew info fish
fish: stable 3.0.0 (bottled), HEAD
User-friendly command-line shell for UNIX-like operating systems
https://fishshell.com
/usr/local/Cellar/fish/3.0.0 (953 files, 8.3MB) *
  Poured from bottle on 2019-01-08 at 09:50:51
…
cadams@tethys ~> sw_vers
ProductName:	Mac OS X
ProductVersion:	10.14.2
BuildVersion:	18C54

[faho]

Indeed. The issue here is of course that $hostname is a read-only variable, so an assertion that "for loop variable should have been successfully set" fails.

[acdha]

I figured it was something like that since it was only pre-defined variables — thanks for the rapid response!

[faho]

Okay, this should be fixed now.

The issue turned out to be specifically for non-"electric" (i.e. evaluated when they are expanded, like $status) read-only variables like $hostname and $SHLVL.

Nice catch!

[ridiculousfish]

Picked into 3.0.1 as f2a1130