I asked the net sifter if Macron was a supply sider:

Yes, French President Emmanuel Macron is widely considered a supply-sider.

I don't know who is represented by "widely". Not every decision to change economic and tax policies can be considered in isolation. It's much more complex than that. France has long had policies that strongly favor "proles", extensive protections for employees, making it impossible to fire or lay off anyone. Generous rules for work hours, time off, sick leave etc. Universal health care. On the tax side it's been quite confiscatory. The result has been widely (there goes notorious "widely" again :-) seen as the reason for a stagnant economy. Sometimes you have to make changes because you've over reached in one direction or the other.

As an example of confiscatory tax policy, I have a cousin who inherited two apartments in Paris from his mother. She had practically no other assets. The inheritance tax was so high that he had to sell one of the two apartments to pay the tax.