Fix large models for strings (#3835)

Fixes #3375.

Marking as "major" since in fact we produce incorrect models in production without the fix.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/theory/strings/theory_strings.cpp b/src/theory/strings/theory_strings.cpp
index c2790fe42..cd1d0cd67 100644
--- a/src/theory/strings/theory_strings.cpp
+++ b/src/theory/strings/theory_strings.cpp
@@ -304,8 +304,13 @@ bool TheoryStrings::collectModelInfo(TheoryModel* m)
     }
     else
     {
-      Assert(len_value.getConst<Rational>() <= Rational(String::maxSize()))
-          << "Exceeded UINT32_MAX in string model";
+      // must throw logic exception if we cannot construct the string
+      if (len_value.getConst<Rational>() > Rational(String::maxSize()))
+      {
+        std::stringstream ss;
+        ss << "Cannot generate model with string whose length exceeds UINT32_MAX";
+        throw LogicException(ss.str());
+      }
       unsigned lvalue =
           len_value.getConst<Rational>().getNumerator().toUnsignedInt();
       std::map<unsigned, Node>::iterator itvu = values_used.find(lvalue);