Rustc oddities
Table of contents
NFC normalisation for lifetime/label
Identifiers are normalised to NFC,
which means that Kelvin and Kelvin are treated as representing the same identifier.
See rfc2457.
But this doesn't happen for lifetimes or labels, so 'Kelvin and 'Kelvin are different as lifetimes or labels.
For example, this compiles without warning in Rust 1.90, while this doesn't.
In this writeup, the represented ident attribute of Ident and Raw_ident fine-grained tokens is in NFC,
and the name attribute of Lifetime_or_label and Raw_lifetime_or_label tokens isn't.
I think this behaviour is a promising candidate for provoking the "Wait...that's what we currently do? We should fix that." reaction to being given a spec to review.
Filed as rustc #126759.
Nested block comments
The Reference says "Nested block comments are supported".
Rustc implements this by counting occurrences of /* and */, matching greedily.
That means it rejects forms like /* xyz /*/.
This writeup includes a !"/*" subexpression in the BLOCK_COMMENT_CONTENT definition to match rustc's behaviour.
The grammar production in the Reference seems to be written to assume that these forms should be accepted
(but I think it's garbled anyway: it accepts /* /* */).
I haven't seen any discussion of whether this rustc behaviour is considered desirable.
String continuation escapes
rustc has a warning that the behaviour of String continuation escapes
(when multiple newlines are skipped)
may change in future.
The Reference has a note about this, and points to #1042 for more information.
#136600 asks whether this is intentional.