fuzz findings [c]: undeclared disagreements (2026-08-24)

[zmaril]

Fuzzing derived programs the grammar and the reference parser disagree on.

• findings: 34 (34 undeclared)
• iterations: 5000
• we_accepted: 2561
• we_rejected: 1308
• agreed: 960
• widenings: 1601
• grammar coverage: 93.5% of alternatives

Undeclared programs the reference parser accepts but our grammar splits differently (34 distinct):

aa

; aa

; # a aa

aa aa { }

aa ( 0 ) ;

---

Filed automatically by piecework.
lang: c · kind: fuzz · grammar: 2ace7ce · corpus depth: 100 packages
ticket: fuzz-c-106505538 (exit 0)

job log tail

valid, 0 invalid, 1 indeterminate, 0 error (of 3 adjudicated)
oracle: verdict detail at /tmp/oracle-verdicts.json
oracle: 2 valid, 0 invalid, 0 indeterminate, 0 error (of 2 adjudicated)
oracle: verdict detail at /tmp/oracle-verdicts.json
oracle: 1 valid, 0 invalid, 0 indeterminate, 0 error (of 1 adjudicated)
oracle: verdict detail at /tmp/oracle-verdicts.json
oracle: 2 valid, 0 invalid, 0 indeterminate, 0 error (of 2 adjudicated)
oracle: verdict detail at /tmp/oracle-verdicts.json
oracle: 1 valid, 0 invalid, 0 indeterminate, 0 error (of 1 adjudicated)
oracle: verdict detail at /tmp/oracle-verdicts.json
oracle: 1 valid, 0 invalid, 0 indeterminate, 0 error (of 1 adjudicated)
oracle: verdict detail at /tmp/oracle-verdicts.json
oracle: 1 valid, 0 invalid, 0 indeterminate, 0 error (of 1 adjudicated)
oracle: verdict detail at /tmp/oracle-verdicts.json
fuzz: 2561 accepted by us (1308 discarded as unfaithful), 960 agreed, 1601 widening(s) in 34 distinct program(s) — 34 undeclared, 0 declared
fuzz: coverage — 730/781 grammar alternatives (93.5%), 173 tape(s) kept
  unreached    7  in preproc_elifdef_in_block
  unreached    7  in preproc_ifdef_in_block
  unreached    5  in preproc_elif_in_block
  unreached    5  in preproc_if_in_block
  unreached    3  in preproc_elifdef_in_enumerator_list
  unreached    3  in switch_body
  unreached    2  in case_clause
  unreached    2  in comment
  436x  aa ⏎ 
   27x  ; aa ⏎ 
   32x  ; # a aa  ⏎ 
  279x  aa aa { } ⏎ 
   46x  aa ( 0 ) ; ⏎ 
   95x  aa aa aa ; ⏎ 
   11x  enum { } ; ⏎ 
  275x  aa aa { } ; ⏎ 
  121x  aa aa aa ; ; ⏎ 
   10x  asm ( L" " ) ; ⏎ 
    2x  void ; # a aa  ⏎ 
   32x  asm ( " " aa ) ; ⏎ 
    2x  asm ( L" " ) ; ; ⏎ 
    3x  void aa ( ) aa ; ⏎ 
    3x  # a undef aa  ⏎  aa ⏎ 
    1x  # a define aa  ⏎  aa ⏎ 
   22x  asm ( " " aa ) ; ; ⏎ 
    2x  # a include aa  ⏎  aa ⏎ 
    1x  enum aa : void { } ; ⏎ 
    5x  struct aa { aa } ; ; ⏎ 
fuzz: report at corpus/c/reports/fuzz.json