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Fix three assertion violations in nseq string solver (#9106)

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- seq_model.cpp: skip trivial memberships in collect_var_regex_constraints;
  SAT leaf nodes can have "" in nullable_regex (trivial) in addition to
  primitive (single-variable) memberships after Brzozowski derivative
  consumption reduces a concrete string membership to empty.

- seq_nielsen.cpp: fix SASSERT(!var) typo in var_ub(); should be SASSERT(var)
  matching the pattern in var_lb().

- seq_regex.cpp: replace VERIFY(re_expr) with null guard in
  minterm_to_char_set(); nullptr means no regex constraint and should
  return the full alphabet, as the test test_minterm_nullptr_is_full expects.


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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>
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Copilot 2026-03-23 13:20:06 -07:00 • committed by GitHub
parent dbdccbff97
commit 1c24c835c9
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3 changed files with 5 additions and 2 deletions
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src/smt/seq_model.cpp
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@ -324,6 +324,8 @@ namespace smt {
SASSERT(sat_node);
for (auto const& mem : sat_node->str_mems()) {
SASSERT(mem.m_str && mem.m_regex);
if (mem.is_trivial())
continue; // empty string in nullable regex: already satisfied, no variable to constrain
VERIFY(mem.is_primitive()); // everything else should have been eliminated already
euf::snode* first = mem.m_str->first();
unsigned id = first->id();