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Add string type support to SMT back-end #8838

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Add string type support to SMT back-end #8838

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3db92f3
Add `string` type support to SMT back-end
tautschnig Feb 23, 2026
84732a2
Update src/solvers/smt2/smt2_conv.cpp
tautschnig Feb 23, 2026
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33 changes: 32 additions & 1 deletion src/solvers/smt2/smt2_conv.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2707,8 +2707,24 @@ void smt2_convt::convert_expr(const exprt &expr)
else if(expr.id() == ID_function_application)
{
const auto &function_application_expr = to_function_application_expr(expr);

// Check for string operations by looking at the function symbol name
std::string fn_name;
if(function_application_expr.function().id() == ID_symbol)
fn_name = id2string(
to_symbol_expr(function_application_expr.function()).get_identifier());

if(fn_name == "Str.Concat" &&
function_application_expr.arguments().size() == 2)
{
out << "(str.++ ";
convert_expr(function_application_expr.arguments()[0]);
out << ' ';
convert_expr(function_application_expr.arguments()[1]);
Comment on lines +2717 to +2723
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Copilot AI Feb 23, 2026

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The str.++ (string concatenation) operation in SMT-LIB 2 can take any number of arguments (including 0, 1, or more than 2), but this implementation only handles exactly 2 arguments. When there are != 2 arguments, it falls through to the else case which will output "Str.Concat" instead of "str.++". Consider removing the size check or handling variable numbers of arguments to ensure all Str.Concat calls are properly converted to str.++.

Suggested change
if(fn_name == "Str.Concat" &&
function_application_expr.arguments().size() == 2)
{
out << "(str.++ ";
convert_expr(function_application_expr.arguments()[0]);
out << ' ';
convert_expr(function_application_expr.arguments()[1]);
if(fn_name == "Str.Concat")
{
out << "(str.++";
for(const auto &op : function_application_expr.arguments())
{
out << ' ';
convert_expr(op);
}

Copilot uses AI. Check for mistakes.
out << ')';
}
// do not use parentheses if there function is a constant
if(function_application_expr.arguments().empty())
else if(function_application_expr.arguments().empty())
{
convert_expr(function_application_expr.function());
}
Expand Down Expand Up @@ -3763,6 +3779,19 @@ void smt2_convt::convert_constant(const constant_exprt &expr)
out << "(_ bv" << (value_int - range_type.get_from()) << " " << width
<< ")";
}
else if(expr_type.id()==ID_string)
{
const std::string &value = id2string(expr.get_value());
out << "\"";
for(char c : value)
{
if(c == '"')
out << "\"\"";
else
out << c;
}
out << "\"";
}
else
UNEXPECTEDCASE("unknown constant: "+expr_type.id_string());
}
Expand Down Expand Up @@ -5991,6 +6020,8 @@ void smt2_convt::convert_type(const typet &type)
UNEXPECTEDCASE("unsuppored range type");
out << "(_ BitVec " << address_bits(size) << ")";
}
else if(type.id()==ID_string)
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Copilot AI Feb 23, 2026

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Inconsistent spacing around the == operator. The codebase convention in this file is to use no spaces (e.g., type.id()==ID_string on line 6025, expr_type.id()==ID_string on line 3782). This line has spaces around == which is inconsistent with the rest of the file.

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out << "String";
else
{
UNEXPECTEDCASE("unsupported type: "+type.id_string());
Expand Down
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