Suggest -U when regex contains \n

[dtolnay]

What version of ripgrep are you using?

ripgrep 0.10.0
-SIMD -AVX (compiled)
+SIMD +AVX (runtime)

How did you install ripgrep?

cargo install

Describe your question, feature request, or bug.

I tried this regex today: rg '=> \{\n *break;'. The output is:

the literal '"\n"' is not allowed in a regex

I would expect this error to suggest passing -U to enable multiline mode, in which that pattern would be allowed.

[BurntSushi]

This seems like a good idea! We already do the same with the -P flag if look-around or backreferences are used.