loplugin:passstuffbyref improved return in canvas and svtools

and for now, ignore methods with params so we don't fall into the trap
of thinking that calls to methods like:
   Bar& foo(Bar &p) { return p; }
can be converted from
   Bar f() { return foo(Bar()); }
to
Bar const & f() { return foo(Bar()); }

Change-Id: Ia3795eb2baf353cb6bec4ebf40451f2789d66ad7
Reviewed-on: https://gerrit.libreoffice.org/47034
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/passstuffbyref.cxx

@@ -402,6 +402,12 @@ bool PassStuffByRef::isReturnExprDisqualified(const Expr* expr)
             FunctionDecl const * calleeFunctionDecl = callExpr->getDirectCallee();
             if (!calleeFunctionDecl)
                 return true;
+            // TODO anything takes a param is suspect because it might return the param by ref.
+            // we could tighten this to only reject functions that have a param of the same type
+            // as the return type. Or we could check for such functions and disallow them.
+            // Or we could force such functions to be annotated somehow.
+            if (calleeFunctionDecl->getNumParams() > 0)
+                return true;
             auto tc = loplugin::TypeCheck(calleeFunctionDecl->getReturnType());
             if (!tc.LvalueReference() && !tc.Pointer())
                 return true;