C front-end/KnR: generate nondet for missing arguments

[tautschnig]

The back-end does not know how to handle nil, and symex would also
generate nondet in such cases, so do the same in the front-end.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Base: 78.34% // Head: 78.34% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (302d06a) compared to base (a53fa0f).
Patch coverage: 93.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5692   +/-   ##
========================================
  Coverage    78.34%   78.34%           
========================================
  Files         1644     1645    +1     
  Lines       190313   190359   +46     
========================================
+ Hits        149097   149135   +38     
- Misses       41216    41224    +8     

Impacted Files	Coverage Δ
jbmc/src/janalyzer/janalyzer_parse_options.cpp	48.58% <ø> (ø)
.../src/java_bytecode/character_refine_preprocess.cpp	54.27% <ø> (ø)
...mc/src/java_bytecode/character_refine_preprocess.h	100.00% <ø> (ø)
jbmc/src/java_bytecode/ci_lazy_methods.h	100.00% <ø> (ø)
jbmc/src/java_bytecode/ci_lazy_methods_needed.cpp	98.41% <ø> (ø)
jbmc/src/java_bytecode/ci_lazy_methods_needed.h	100.00% <ø> (ø)
jbmc/src/java_bytecode/code_with_references.cpp	84.61% <ø> (ø)
jbmc/src/java_bytecode/java_bmc_util.cpp	100.00% <ø> (ø)
...mc/src/java_bytecode/java_bytecode_convert_class.h	0.00% <ø> (ø)
...src/java_bytecode/java_bytecode_convert_method.cpp	97.69% <ø> (ø)
... and 412 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[kroening]

This deviates quite a lot from the usual pattern: this would be the only place in the front-end where we pick nondeterministic semantics.

[tautschnig]

This deviates quite a lot from the usual pattern: this would be the only place in the front-end where we pick nondeterministic semantics.

Should we instead handle this case in goto-symex, translating nil to nondet?

[peterschrammel]

At some point it needs to be replaced (frontend, goto, or symex). Having nil in the goto model doesn't seem right, and symex is certainly too late, IMO.