foo.nix: Parses differently after formatting. This is a bug in nixfmt. Please report it at https://github.com/NixOS/nixfmt

Before formatting:
Term (IndentedString (Ann [] [[TextPart "O='''${A}'"],[]] Nothing))

After formatting:
Term (IndentedString (Ann [] [[TextPart "O='''",Interpolation Term (Token (Ann [] (Identifier "A") Nothing)),TextPart "'"],[]] Nothing))