A new lint for an assignment statement a = b = c

[fiveseven-lambda]

What it does

regarding to: https://stackoverflow.com/questions/65661530/why-can-assignment-operator-be-chained-in-rust

One might assume an assignment statement a = b = c; to be equivalent to a = c; b = c;, but it isn't.

There seems to be very few cases, if any, where we would intentionally write a = b = c;.

It would be nice if clippy warned such an assignment.

Categories (optional)

• Kind: correctness

Drawbacks

None.

Example

a = b = c;

Could be written as:

b = c;
a = ();

Or the programmer might have intended:

a = c;
b = c;

[camsteffen]

In practice, I think the programmer will just run into a type error. (Playground)

[fiveseven-lambda]

@camsteffen You used Vec::with_capacity in your example function, but if you only try debug print like this, it compiles with no warning about a = b = c;.

[roynrishingha]

@rustbot claim