I've seen some code lately where a reminder about the !r format specifier would probably have helped - instead of displaying the repr, single-quotes were manually added outside the braces as in f"No value found at '{path}'". This OK, until path contains a single-quote character and then it can get confusing fast.

I'd therefore propose warning about this case, which is conveniently easy to reliably detect using the JoinedStr and FormattedValue nodes - within a JoinedStr, warn if there is a sequence of Constant/FormattedValue/Constant, where the first constant ends and the second starts with a single or double quote character, and the formatter value has no conversion code.

Separately, I used the regex ".*('\{[^}]+\}').*" to confirm that this is common enough to be worth linting for. It's not especially rare, and IMO pretty useful to teach people about format specifiers.