Understanding interaction between visual, autoindent, and paste option

Question

Let's start form this faulty C++ source file

#include <vector>
int main() {
    std::vector<std::vector<int>> v{
            1,2},
            9,3},
            4,2}
    };
}

which is a legit transitory state if you've just copied those 6 numbers from a space-separated text file with two columns.

The last step is to add opening braces on the three lines, so you might put the cursor on the 1, and then go Ctrl-v2jI{Escape. Doing so, however, you end up with this,

#include <vector>
int main() {
    std::vector<std::vector<int>> v{
        {1,2}
            1,1}
            1,2}
    };
}

because the auto indentation pulled the line where the cursor initially is to the left (for whatever reason will be explained in this previous question), i.e. it deleted text, thus breaking out of the block visual mode.

However, if that key sequence is used after :set paste, then the edit is as desired.

I'd like to know how these things play together.

Answer 1

It looks like the reason why :set paste solves the issue is that, among other things, it deactivates cindent, and cindent makes use of cinkeys's default value, which triggers the reindentation if one types { (or other characters) at the beginning of the line.