Raise clear error when freeReoptSolve is called without reoptimization enabled (#624)

Author: Joao-Dionisio

src/pyscipopt/scip.pxd

@@ -1550,6 +1550,7 @@ cdef extern from "scip/scip.h":
     SCIP_RETCODE SCIPfreeReoptSolve(SCIP* scip)
     SCIP_RETCODE SCIPchgReoptObjective(SCIP* scip, SCIP_OBJSENSE objsense, SCIP_VAR** vars, SCIP_Real* coefs, int nvars)
     SCIP_RETCODE SCIPenableReoptimization(SCIP* scip, SCIP_Bool enable)
+    SCIP_Bool SCIPisReoptEnabled(SCIP* scip)
 
     BMS_BLKMEM* SCIPblkmem(SCIP* scip)
 

src/pyscipopt/scip.pxi

@@ -3973,6 +3973,17 @@ cdef class Model:
         """
         PY_SCIP_CALL(SCIPenableReoptimization(self._scip, enable))
 
+    def isReoptEnabled(self):
+        """
+        Returns whether reoptimization is enabled.
+
+        Returns
+        -------
+        bool
+
+        """
+        return SCIPisReoptEnabled(self._scip)
+
     def lpiGetIterations(self):
         """
         Get the iteration count of the last solved LP.
@@ -11950,6 +11961,10 @@ cdef class Model:
     def freeReoptSolve(self):
         """Frees all solution process data and prepares for reoptimization."""
 
+        if not SCIPisReoptEnabled(self._scip):
+            raise ValueError("freeReoptSolve requires reoptimization to be enabled. "
+                             "Call enableReoptimization() before solving.")
+
         if self.getStage() not in [SCIP_STAGE_INIT,
                                  SCIP_STAGE_PROBLEM,
                                  SCIP_STAGE_TRANSFORMED,

src/pyscipopt/scip.pyi

@@ -1454,6 +1454,7 @@ class Model:
     def isObjChangedProbing(self) -> Incomplete: ...
     def isObjIntegral(self) -> Incomplete: ...
     def isPositive(self, val: Incomplete) -> Incomplete: ...
+    def isReoptEnabled(self) -> bool: ...
     def isZero(self, value: Incomplete) -> Incomplete: ...
     def lpiGetIterations(self) -> Incomplete: ...
     def markDoNotAggrVar(self, var: Incomplete) -> Incomplete: ...