Fix reference to temporary that has gone out of scope

[tautschnig]

Store language_mode by value instead of by reference in goto_symex_statet. The copy is cheap (irep_idt is an interned string index) and eliminates the dangling-reference problem at the root: the class now owns its data, so callers need not worry about the lifetime of the argument.

Co-authored-by: Kiro kiro-agent@users.noreply.github.com

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[Copilot]

Pull request overview

Fixes undefined behavior in unit tests caused by passing a temporary irep_idt{} into constructors that (directly or indirectly) store references, ensuring the referenced object outlives the constructed test fixtures.

Changes:

• Introduce a named empty_language_mode variable to give the language-mode argument a stable lifetime.
• Replace uses of irep_idt{} temporaries with the named variable in affected test constructions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
unit/goto-symex/symex_assign.cpp	Avoids dangling reference by binding language-mode to a local variable reused across multiple constructions.
unit/goto-symex/goto_symex_state.cpp	Same lifetime fix for goto_symex_statet construction in state unit test.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.01%. Comparing base (eee45a7) to head (f279121).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8866   +/-   ##
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  Coverage    80.00%   80.01%           
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  Files         1703     1703           
  Lines       188397   188397           
  Branches        73       73           
========================================
+ Hits        150736   150742    +6     
+ Misses       37661    37655    -6     

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[kroening]

May I suggest changing the reference const irep_idt &language_mode in goto-symex/goto_symex_state.h to a copy instead. The copy is cheap.

[tautschnig]

May I suggest changing the reference const irep_idt &language_mode in goto-symex/goto_symex_state.h to a copy instead. The copy is cheap.

Thanks, done. Updated the commit & PR description accordingly.