What is the meaning of [你说什么是什么]?

It means the person who says this wants to just give up arguing. It can be translated as:

"Well, whatever" (accompanied by a shrug, or polite smile)

The meaning of this sentence is very vague. My mother tongue is Chinese, but without the help of context, I have no idea what it means. Even if there is a context, there may be a deviation in understanding.

This person is not very good at expressing his ideas, or deliberately speaking very vague.

The expression of smiling face has the meaning of being angry in young people's communication.

"Damn, whatever the f*** you say, I'll take it... I guess"

Said with a cynical voice.

Could be two meanings

1. you decide (more likely)
2. implying you are too dominating (less likely)

it also depends on what kind of smiley emoji they send you. If it's a "slightly smile" emoji, than it raises a red alarm.

The whole meaning of the pattern 说什么是什么 varies according to contexts. In (a), this pattern means someone is honest; in (b), it means the speaker is forced by authority to agree. a. 我们不是那心口两样的人，说什么是什么。 b. 您官大一品，您说什么是什么 。

In terms of cognitive semantics, its core meaning description is that the potential event expressed by 说什么 could be fulfilled by the act by 是什么 despite of any unexpected or expected intervention.

You two may have a disscusion, and that people said this to you ? Most time , this people is too tired to argue with you.

also see:

千万不要和傻子争论,你就和他说你说的对就行了。他就会心满意足的走了

I think Pedroski got it right.

"你说什么是什么" = "你说什么(就)是什么。" = "Whatever you say (, then whatever it will be)."

"你说什么(就)是什么。" can be used literally. For example "主席说你是人民公敌，你(就)是人民公敌" - The chairman said you are the enemy of the people, (then) you are the enemy of the people.

In most cases, it is used sarcastically. For example "你說我不是好人，我(就)不是好人" - You say I am a bad person, (then) I am a bad person

My conclusion is, yes, he meant 'Whatever you say.'. Not that he is agreeing with you, but more like "I am not arguing with you"

你说什么是什么。

The sentence usually is used when someone disagree with you or they don't know the right answer and whether you said is true or not, but they don't want to argue with you probably because they think it's useless or they feel they can do nothing to influence your decision or believe.

It could be something like believe or do whatever you said because I have no influence on you about it or we don't know the real truth about it.. Or it could be that there are many ways to take it and you can decide whichever you like.

Again, we need more context to analyze what your friend truly means. It could be either he disagreed with you but don't want to argue or he doesn't know the truth either so he just left the decision to you or either way is correct and you can decide which one you should pick.

The sentence could be a wry way to agree with someone. And that smiley emoji is probably just to not make you sad about it.

Like you said, your friend's sentence might be to convey:

"Whatever you say is what you say, I won't complain/disagree."

I guess it'll depend on context, like what the conversation is about etc. Did he/she reply to an answer, etc.

According to this article, the smiley emoji can mean something else: https://www.techinasia.com/smiley-face-emoji-meaning-china

Maybe you mean:

你说什么就是什么。

You decide.