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Implement ZIPT string solver skeleton (theory_nseq)

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Add theory_nseq, a Nielsen-graph-based string solver plugin for Z3.

## New files
- src/smt/nseq_state.h/.cpp: constraint store bridging SMT context to
  Nielsen graph with manual push/pop backtracking
- src/smt/nseq_regex.h/.cpp: regex membership handling via Brzozowski
  derivatives (stub delegates to sgraph::brzozowski_deriv)
- src/smt/nseq_model.h/.cpp: model generation stub
- src/smt/theory_nseq.h/.cpp: main theory class implementing smt::theory
  with its own private egraph/sgraph, returns FC_GIVEUP as skeleton
- src/test/nseq_basic.cpp: unit tests covering instantiation, parameter
  validation, trivial-equality SAT, and node simplification

## Extensions to seq_nielsen.h/.cpp
- Add search_result enum and solve() iterative-deepening DFS entry point
- Add search_dfs() recursive DFS driver
- Add simplify_node(), generate_extensions(), collect_conflict_deps()
- Add nielsen_node::simplify_and_init(): trivial removal, empty
  propagation, prefix matching, symbol clash detection
- Add nielsen_node::is_satisfied(), is_subsumed_by()
- Implement Det, Const Nielsen, and Eq-split modifiers in
  generate_extensions()

## Integration
- smt_params.cpp: accept 'nseq' as valid string_solver value
- smt_params_helper.pyg: document 'nseq' option
- smt_setup.h/.cpp: add setup_nseq(), wire into setup_QF_S() and
  setup_seq_str()
- smt/CMakeLists.txt: add new sources and smt_seq dependency

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
copilot-swe-agent[bot] 2026-03-03 21:50:21 +00:00
parent a7084de5a8
commit 0bdec633d7
18 changed files with 997 additions and 6 deletions
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4
src/params/smt_params.cpp
View file

@ -187,9 +187,9 @@ void smt_params::display(std::ostream & out) const {
}
void smt_params::validate_string_solver(symbol const& s) const {
if (s == "z3str3" || s == "seq" || s == "empty" || s == "auto" || s == "none")
if (s == "z3str3" || s == "seq" || s == "empty" || s == "auto" || s == "none" || s == "nseq")
return;
throw default_exception("Invalid string solver value. Legal values are z3str3, seq, empty, auto, none");
throw default_exception("Invalid string solver value. Legal values are z3str3, seq, empty, auto, none, nseq");
}
void smt_params::setup_QF_UF() {

2
src/params/smt_params_helper.pyg
View file

@ -122,7 +122,7 @@ def_module_params(module_name='smt',
('dack.gc_inv_decay', DOUBLE, 0.8, 'Dynamic ackermannization garbage collection decay'),
('dack.threshold', UINT, 10, ' number of times the congruence rule must be used before Leibniz\'s axiom is expanded'),
('theory_case_split', BOOL, False, 'Allow the context to use heuristics involving theory case splits, which are a set of literals of which exactly one can be assigned True. If this option is false, the context will generate extra axioms to enforce this instead.'),
('string_solver', SYMBOL, 'seq', 'solver for string/sequence theories. options are: \'z3str3\' (specialized string solver), \'seq\' (sequence solver), \'auto\' (use static features to choose best solver), \'empty\' (a no-op solver that forces an answer unknown if strings were used), \'none\' (no solver)'),
('string_solver', SYMBOL, 'seq', 'solver for string/sequence theories. options are: \'z3str3\' (specialized string solver), \'seq\' (sequence solver), \'auto\' (use static features to choose best solver), \'empty\' (a no-op solver that forces an answer unknown if strings were used), \'none\' (no solver), \'nseq\' (Nielsen-based string solver)'),
('core.validate', BOOL, False, '[internal] validate unsat core produced by SMT context. This option is intended for debugging'),
('seq.split_w_len', BOOL, True, 'enable splitting guided by length constraints'),
('seq.validate', BOOL, False, 'enable self-validation of theory axioms created by seq theory'),