allow ID_index expressions in history variables

Author: SaswatPadhi

regression/contracts/history-index/main.c

@@ -0,0 +1,14 @@
+#include <assert.h>
+
+int main()
+{
+  int i, n, x[10];
+  __CPROVER_assume(x[0] == x[9]);
+  while(i < n)
+    __CPROVER_loop_invariant(x[0] == __CPROVER_loop_entry(x[0]))
+    {
+      x[0] = x[9] - 1;
+      x[0]++;
+    }
+  assert(x[0] == x[9]);
+}

regression/contracts/history-index/test.desc

@@ -0,0 +1,10 @@
+CORE
+main.c
+--apply-loop-contracts
+^EXIT=0$
+^SIGNAL=0$
+^VERIFICATION SUCCESSFUL$
+--
+^Tracking history of index expressions is not supported yet\.
+--
+This test checks that `ID_index` expressions are allowed within history variables.

src/goto-instrument/contracts/contracts.cpp

@@ -664,7 +664,8 @@ void code_contractst::replace_history_parameter(
     const auto &id = parameter.id();
     if(
       id == ID_dereference || id == ID_member || id == ID_symbol ||
-      id == ID_ptrmember || id == ID_constant || id == ID_typecast)
+      id == ID_ptrmember || id == ID_constant || id == ID_typecast ||
+      id == ID_index)
     {
       auto it = parameter2history.find(parameter);