clang isConstQualified() method does not work with const placement

Question

I'm trying to implement a clang-tidy check to warn about the use of output parameters.

As registerMatchers method, I have the following:

void AvoidouputparametersCheck::registerMatchers(MatchFinder *Finder) {
    Finder->addMatcher(
          functionDecl(isDefinition(), hasBody(stmt()), hasAnyParameter(decl())).bind("function"),
          this);
}

As check method, I have the following:

void AvoidouputparametersCheck::check(const MatchFinder::MatchResult &Result) {
    const auto *Function = Result.Nodes.getNodeAs<FunctionDecl>("function");
    for (unsigned i = 0, e = Function->getNumParams(); i != e; ++i) {
        const auto *Param = Function->getParamDecl(i);
        if(!Param->getType().getCanonicalType().isConstQualified() && Param->getType().getTypePtr 
        ()->isReferenceType())
             auto MyDiag = diag(Param->getLocation(), "avoid output parameters") << Param;
    }

If I run clang-tidy I have the following warnings:

void foo(int a &){} warning: output parameter

void foo(const int &a){}

void foo(int const &a){} warning: output parameter

When I place const in the right hand side of the type, clang does not detect it as a const qualified parameters.