Public discussions of traditional Islamic law, by both supporters and critics, routinely refer to the law as Shari'a. As best I can tell, that is a mistake. Islamic law as it was interpreted by legal scholars and applied in the traditional court system is fiqh. Shari'a is what fiqh would be if the scholars always got it right, something they have never claimed to do. Think of it as law in the mind of God.
The same distinction exists in American constitutional law, even though we confusingly use the same word for both concepts. If a lower level court rules a law unconstitutional, it is making a statement not about the Constitution but about the views of the Supreme Court. Roughly speaking, "this law is unconstitutional" is the prediction that, if the case gets to the Supreme Court, the law will be struck down.
But consider the same question from the standpoint of a Supreme Court justice. His vote is not a prediction of how he and his colleagues will vote, it is a statement about how they should vote. If he ends up in the minority, the implication is not that he is wrong, only that his view failed to prevail. While his vote may, under the principle of stare decisis, be influenced by past votes of past justices, what determines it is his view of what the Constitution says and how it ought to be interpreted.
A constitutional scholar is likely to use "constitutional" in both senses. In some contexts, the question he is interested in is how the Supreme Court can be expected to rule. In others, it is how it ought to rule.
Think of "constitutional" in the Justice's sense as "constitutional (1)," in the lower court's sense as "constitutional (2)." Shari'a in traditional Islamic law corresponds to constitutional (1) in our system. Fiqh corresponds to constitutional (2).