Rustc oddities
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.
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.