Hcl (g)+H2O=H3O+cl In this reaction HCl is in gas state so it is not an acid but it donate a proton so it must be acid ?

According to Brϕnsted-Lowry theory, HCl is an acid because it is a proton donor in the reaction.

there are several errors in the form that you really should not allow to happen (Cl- and H3O+; Cl not cl). notation is important. CO is not Co. Is the water a gas too? Well, doesn't actually matter to your question: you have a loose proton that separates from an ionic compound so the compound is acting as an acid (releasing H+). Strictly speaking, if the water is liquid, then you have to first dissolve the HCl gas into it, and you would then have HCl (g) = HCl (aq) and the HCl (aq) would immediately separate into H+ and Cl- (both also aqueous), so the gaseous HCl would not be what was ionizing. The same sort of idea that applies to CO2. CO2 is an acid forming gas but not an acid per se although we can call it that depending on how you define the word "acid". CO2 gas dissolves first (making aqueous CO2) which relatively rapidly reacts with water liquid to make H2CO3, which then acts as the acid.

So, in your example, I would call the HCl gas an "acid". I would prefer to call it an acid-forming gas, although we tend to use that term for compounds that have to react with water to make the acid (like CO2, NO, NO2, or SO2, etc.) The gas doesn't ionize while a gas. HCl can react directly with other substances than water and it will act as an acid in many such situations, but it doesn't really spontaneously acidify in its pure gaseous state. So HCl gas isn't an acid, which is what you said, yet the reaction that you provide requires that it is an acid. And the problem is that the reaction, as written, is not precisely correct.