All I did was

Because it is not idiomatic, and native speakers will think your English sounds odd.

Is there any rule about this?

AnonymousIs there any rule about this?

The verb "do" in the subject clause is completed by a bare infinitive in the main sentence.

All we did at the party was eat and drink. (We did eat and drink at the party, and didn't do anything else.)
All he does is complain. (He does complain, and does nothing else)

Compare wi

Thanks for the enlightment.What I've have done is eat.What exactly is the structure?

It is a different structure than your previous post. The grammatical subject is the underlined clause.

What I have done is (I have) eaten all the cookies. (past participle is used after "have")

What I did was (I did) eat all the cookies. (infinitive is used after "do")

What I do is (I do) eat all the cookies.

Wh

It's much appreciated.I've a one more question.What I have done is eat Is it grammatically correct? I've seen this a lot on the internet.

AnonymousWhat I have done is eat.

OK. Most grammarians say that you can use the plain form of the verb to match any form of do except doing. Use the -ing form to match doing.

What I [do / will do / did / have done / should do / must have done / need to do / ... ] is eat.
What I [am doing / was doing / have b