Rustc oddities
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 1.86, while this doesn't.
In this writeup, the represented identifier attribute of Identifier and RawIdentifier fine-grained tokens is in NFC,
and the name attribute of LifetimeOrLabel and RawLifetimeOrLabel 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.