The poster was Misha's dream come true.

[*^^*]

Is the first sentence even correct? "The poster was Misha's come true." There are two predicates in this sentence. Shouldn't it be like " The poster could make Misha's dream come true."?

 

[5jj]

The poster was Misha's dream come true" is OK grammatically.

In real life, the poster was not her dream come true. Had she been accepted by the band, that would have been her dream come true.

 

[emsr2d2]

If she had always dreamt of seeing a poster saying the band were looking for guitarist, then the poster would have been her dream come true.

 

[Skrej]

'A dream come true' or the variant 'X is a dream come true' are both very common and completely natural phrases.

As to the sentence in question - I don't think the poster itself was the dream come true (although that's how it's literally phrased), but rather the opportunity offered by the poster.

 

[SoothingDave]

Think of it as "her dream (that had) come true."

 

[*^^*]

'A dream come true' or the variant 'X is a dream come true' are both very common and completely natural phrases.

As to the sentence in question - I don't think the poster itself was the dream come true (although that's how it's literally phrased), but rather the opportunity offered by the poster.

Thank you Skrej. I know the meaning of the sentence, just confused of the grammar as a nonnative speaker.
"A dream came true. A dream will come true. A dream comes true. " are all understandable. but "A dream come true"?
and how to understand this structure grammatically, "X is +a full sentence."?

 

[Ostap]

Think of "a dream come true" as a fixed expression instead of a "a full sentence".

 

[dunchee]

Thank you Skrej. I know the meaning of the sentence, just confused of the grammar as a nonnative speaker.
"A dream came true. A dream will come true. A dream comes true. " are all understandable. but "A dream come true"?
and how to understand this structure grammatically, "X is +a full sentence."?

Grammatically, it's a noun phrase, not a sentence. I'll borrow SoothingDave's reply in #5:

... "her dream (that had) come true"​

The whole thing is a noun phrase -- "come true"(without "that had") is a participial phrase(*1) modifying "her dream".

So to answer your question, "X is +a full sentence", it's actually "X is + a noun phrase".

This might also help: (it agrees with what Ostap said in #7)

be a dream come true | meaning of be a dream come true in Longman Dictionary of Contemporary English | LDOCE

be a dream come true meaning, definition, what is be a dream come true: if something is a dream come true, it ha...: Learn more.

www.ldoceonline.com

(*1) some would call this a participial clause