private Statement rewriteCondition(Statement conditionStat, Expression conditionExpr, Expression message, boolean explicit) {
    Statement result = rewriteCondition(conditionExpr, message, explicit);
    result.setSourcePosition(conditionStat);
    return result;
  }
Rewrites explicit ("assert x > 3") and implicit ("x > 3") condition
statements. Replacing the original statement with the rewritten one is up
to clients.

@author Peter Niederwieser
spock-core/src/main/java/org/spockframework/compiler/ConditionRewriter.java