Incorrect reference flags for x++ and x--

[overlookmotel]

let x;
x += 1;
x++;
++x;
x--;
--x;

x += 1 gets correctly flagged as Read | Write. But all the rest (x++ etc) are flagged as just Write. This appears to be incorrect.

playground

[Dunqing]

This seems to be intentional

oxc/crates/oxc_semantic/src/lib.rs

Lines 273 to 277 in e4b3a3c

	// unary op counts as write, but checking continues up tree
	(SourceType::default(), "let a = 1, b; b = ++a", ReferenceFlag::read_write()),
	(SourceType::default(), "let a = 1, b; b = --a", ReferenceFlag::read_write()),
	(SourceType::default(), "let a = 1, b; b = a++", ReferenceFlag::read_write()),
	(SourceType::default(), "let a = 1, b; b = a--", ReferenceFlag::read_write()),

Same behavior in no_unused_private_class_members rule

oxc/crates/oxc_linter/src/rules/eslint/no_unused_private_class_members.rs

Lines 331 to 337 in e4b3a3c

	r"class C {
	#usedOnlyInIncrement;
	foo() {
	this.#usedOnlyInIncrement++;
	}
	}",

But I think x += 1 should be flagged as Write because x is never used for reading. I believe this variable can be safely removed by the Minifier/Compressor.

Does this make sense?

[overlookmotel]

Hmm. I'm not clear what these flags are meant to represent now!

These are all (broadly) equivalent:

x = x + 1; // Read + Write
x += 1; // Read | Write
x++; // Write
++x; // Write

NB: Also depends on what x is. If it's an object with a valueOf method, the any of the above can have side effects.

This also seems to be inconsistent - it flags x as Read | Write where it could be just Write:

let x = 1;
let y = x = 2;

playground

And something strange going on here - the addition of console.log makes x Read | Write:

console.log;
let x = 1;
x++;

playground

[Dunqing]

Hmm. I'm not clear what these flags are meant to represent now!
These are all (broadly) equivalent:

x = x + 1; // Read + Write
x += 1; // Read | Write
x++; // Write
++x; // Write

The x = x + 1 is not equivalent. This assignment expression has two references. x + 1 will be flagged Read and x = will be flagged Write

NB: Also depends on what x is. If it's an object with a valueOf method, the any of the above can have side effects.

Yes! I forgot the valueOf method.

This also seems to be inconsistent - it flags x as Read | Write where it could be just Write:

let x = 1;
let y = x = 2;

playground

This case is correct. x = 2 should be flagged as Write and y = x should be flagged as Read

And something strange going on here - the addition of console.log makes x Read | Write:

console.log;
let x = 1;
x++;

playground

This is a bug! I will fix it.

[magic-akari]

This case is correct. x = 2 should be flagged as Write and y = x should be flagged as Read

Here, x should be marked as Write, and y should also be marked as Write.
x will not be Read; x = 2 returns the return value of the assignment expression, not the value read from x.

Please refer to:
https://x.com/magic_akari/status/1713914879449661734