`==` after unsafe block is not correctly recognized

[upsuper]

Given the following code:

let mut a = std::mem::MaybeUninit::new(10);
unsafe { std::ptr::read(a.as_ptr()) } == 10;

Rust reports error:

error: expected expression, found `==`
 --> src/main.rs:3:43
  |
3 |     unsafe { std::ptr::read(a.as_ptr()) } == 10;
  |                                           ^^ expected expression

However, if I change == to +, Rust would instead mentions that a pair of parens should be added to wrap the block:

error: expected expression, found `+`
 --> src/main.rs:3:43
  |
3 |     unsafe { std::ptr::read(a.as_ptr()) } + 10;
  |     ------------------------------------- ^ expected expression
  |     |
  |     help: parentheses are required to parse this as an expression: `(unsafe { std::ptr::read(a.as_ptr()) })`

I guess the error message should probably be updated for the == case as well.

[hellow554]

- is not working as well ^^

@rustbot claim

[hellow554]

@rustbot modify labels: A-suggestion-diagnostics C-enhancement T-compiler

[hellow554]

According to

rust/src/libsyntax/util/parser.rs

Lines 213 to 232 in a605441

	pub fn can_continue_expr_unambiguously(&self) -> bool {
	use AssocOp::*;
	match self {
	BitXor | // `{ 42 } ^ 3`
	Assign | // `{ 42 } = { 42 }`
	Divide | // `{ 42 } / 42`
	Modulus | // `{ 42 } % 2`
	ShiftRight | // `{ 42 } >> 2`
	LessEqual | // `{ 42 } <= 3`
	Greater | // `{ 42 } > 3`
	GreaterEqual | // `{ 42 } >= 3`
	AssignOp(_) | // `{ 42 } +=`
	LAnd | // `{ 42 } &&foo`
	As | // `{ 42 } as usize`
	// Equal | // `{ 42 } == { 42 }` Accepting these here would regress incorrect
	// NotEqual | // `{ 42 } != { 42 } struct literals parser recovery.
	Colon => true, // `{ 42 }: usize`
	_ => false,
	}
	}

== cannot really be used. But I guess I can fix -, |, etc.

[upsuper]

I mean, yes == probably cannot be used, but the error message should be more clear just like when using +.

[JohnTitor]

Triage: I'm going to release assignment due to inactivity.
@hellow554 If you're still interested in this, feel free to re-claim.
@rustbot release-assignment