'as', '<' and '*' can cause a parsing error

[keeperofdakeys]

The following code snippet is causing an error that might be avoidable (I suspect a parsing error, but I don't know how the grammar is actually defined, so this is just a guess). The error is "bare raw pointers are no longer allowed".

fn main() { let a = &4u64; println!("{}", 43 as u64 < *a);

I suspect that the *a is being interpreted as the start of a type generic, when it's actually dereferencing a value. Adding brances '( ... )' fixes the issue, as well as reordering the statement into a '>'. The problem occurs on both stable and nightly.

[keeperofdakeys]

Thinking about this a bit further, the 'bare raw pointers' error must be occurring very early in the parsing (lexer?) in order to trigger that early. The less-than doesn't even have a matching angle-bracket.

[petrochenkov]

The parser expects a type after as, so it starts parsing u64 < *a as a type.
If we rename the identifiers and remove whitespaces things become more evident - we have Type<*T and < is interpreted as a start of type parameters and * is interpreted as a start of a pointer type which should be followed by const or mut, but is followed by T, therefore the error.

The specialized error message about bare raw pointers should probably be removed - it's a pre-1.0 feature and only gray-bearded elders remember about them.

[birkenfeld]

Compiler now says

x.rs:1:55: 1:56 error: expected mut or const in raw pointer type (use`_mut T`or`_const T` as appropriate)
x.rs:1 fn main() { let a = &4u64; println!("{}", 43 as u64 < *a);

Otherwise, this is a duplicate of #22644 and #11962.

[Mark-Simulacrum]

Closing in favor of #22644.