erlang: fix spawn_link

[ilya-klyuchnikov]

1. Remove MF clauses - those are just crashing

1> erlang:spawn_link({erlang, self}).
=ERROR REPORT==== 11-Jul-2025::10:00:24.949585 ===
Error in process <0.90.0> with exit value:
{{badfun,{erlang,self}},[{erlang,apply,2,[]}]}

** exception exit: {badfun,{erlang,self}}
     in function  apply/2

2> erlang:spawn_link(erlang:node(), {erlang, self}).
=ERROR REPORT==== 11-Jul-2025::10:13:09.738964 ===
Error in process <0.89.0> with exit value:
{{badfun,{erlang,self}},[{erlang,apply,2,[]}]}

** exception exit: {badfun,{erlang,self}}
     in function  apply/2

2. More precise guards: is_function(F) -> is_function(F, 0)
3. More precise types

---

Bad code found by eqwalizer.

[github-actions]

CT Test Results

    3 files    142 suites   49m 40s ⏱️
1 649 tests 1 592 ✅ 57 💤 0 ❌
2 372 runs  2 295 ✅ 77 💤 0 ❌

Results for commit 708dbcb.

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// Erlang/OTP Github Action Bot

[jhogberg]

Thanks for the PR!

This is a rather funny one as the usage doesn't crash the caller. It crashes the spawned process, so from the caller's point of view the spawning of the process was a success. Fixing this could break strange but otherwise working code. I don't expect that to be a problem but it's something we need to discuss internally.

Edit: we'll merge this to master soon.

[jhogberg]

As an aside the {M, F} form is a holdover from when funs were tuples. This 2-tuple form was used to represent exported functions (fun M:F/A), and worked all the way until ~R15 in 2011.