OTP 26 shell edlin_expand crash with invalid autocomplete

[potatosalad]

Describe the bug

This was originally discovered when doing some property-based tests involving autocomplete in the OTP 26 shell.

The input a:x(b:y(c:z(a:x(0b:y(c:z(0) followed by pressing <TAB> results in a crash inside edlin_expand:

Erlang/OTP 26 [erts-14.2.1] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Eshell V14.2.1 (press Ctrl+G to abort, type help(). for help)
*** ERROR: Shell process terminated! ***
=ERROR REPORT==== 11-Jan-2024::13:16:57.319921 ===
Error in process <0.70.0> with exit value:
{{bad_generator,{no,[],[]}},
 [{edlin_expand,'-expand_function_type/6-lc$^0/1-0-',2,
                [{file,"edlin_expand.erl"},{line,573}]},
  {edlin_expand,expand_function_type,6,[{file,"edlin_expand.erl"},{line,573}]},
  {edlin_expand,expand,3,[{file,"edlin_expand.erl"},{line,108}]},
  {group,get_line1,5,[{file,"group.erl"},{line,664}]},
  {group,get_chars_loop,10,[{file,"group.erl"},{line,498}]},
  {group,io_request,6,[{file,"group.erl"},{line,202}]},
  {group,server_loop,3,[{file,"group.erl"},{line,128}]}]}

Eshell V14.2.1 (press Ctrl+G to abort, type help(). for help)
1> a:x(b:y(c:z(a:x(0b:y(c:z(0)1>

After manually shrinking the counterexample, it looks like 0:a( plus <TAB> is all that is needed to cause the crash:

Erlang/OTP 26 [erts-14.2.1] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Eshell V14.2.1 (press Ctrl+G to abort, type help(). for help)
*** ERROR: Shell process terminated! ***
Eshell V14.2.1 (press Ctrl+G to abort, type help(). for help)
1> 0:a(=ERROR REPORT==== 11-Jan-2024::13:18:58.846408 ===
Error in process <0.70.0> with exit value:
{{bad_generator,{no,[],[]}},
 [{edlin_expand,'-expand_function_type/6-lc$^0/1-0-',2,
                [{file,"edlin_expand.erl"},{line,573}]},
  {edlin_expand,expand_function_type,6,[{file,"edlin_expand.erl"},{line,573}]},
  {edlin_expand,expand,3,[{file,"edlin_expand.erl"},{line,108}]},
  {group,get_line1,5,[{file,"group.erl"},{line,664}]},
  {group,get_chars_loop,10,[{file,"group.erl"},{line,498}]},
  {group,io_request,6,[{file,"group.erl"},{line,202}]},
  {group,server_loop,3,[{file,"group.erl"},{line,128}]}]}

1>

To Reproduce

1. Start an OTP 26 shell with erl
2. Type in 0:a(
3. Hit <TAB> to trigger autocomplete
4. The shell will crash and restart itself

Alternatively, the following may be executed directly:

1> edlin_expand:expand(lists:reverse("0:a("), []).
** exception error: bad generator {no,[],[]}
     in function  edlin_expand:'-expand_function_type/6-lc$^0/1-0-'/2 (edlin_expand.erl, line 573)
     in call from edlin_expand:expand_function_type/6 (edlin_expand.erl, line 573)
     in call from edlin_expand:expand/3 (edlin_expand.erl, line 108)

Expected behavior

This behavior is not present in OTP 25. The shell should not crash due to an autocomplete error.

See output on OTP 25 for comparison:

1> edlin_expand:expand(lists:reverse("0:a(")).
{no,[],[]}

Affected versions

OTP 26.2.1 (and all other versions of OTP 26 as far as I've tested)

[garazdawi]

Fixed in #8075