Could we deprecate the use of numeric literal suffixes without _ separating them from the value? I.e., these would no longer be allowed:
5i32
2.3e10f64
Instead, the permitted way to write them would be:
5_i32
2.3e10_f64
Additionally, to catch the specific bug that inspired that thread, could we consider requiring a type suffix when using the exponent (e or E) literal notation? I.e., this would no longer be permitted:
I think the path for that would be a default-allow lint, and add it to rust-2021-idioms. This is mostly a style issue though, so I don't think it's necessary to go for a breaking change.
To me this feels like a stylistic choice, so I'd don't think I'd ever be in favour of making it a hard error.
Of course, I always use underscored suffixes myself so I'd be fine with making a warn-by-default lint about it, though I'm not sure whether that would be better in clippy or rustc.
(Really I wish we could just have 1.0: f32 instead of the suffixes, but that doesn't seem like it's happening any time soon.)