In Rust issue #28160, Niko shows an example containing the line x += { x = 20; 2 }, and asks the question what execution order should be used.

I think we should have a lint against those degenerate cases. However, I'm not sure what patterns we should match.

issues left:

• simple cases with one variable
• struct/tuple fields (easy)
• taking a reference to a field stops the lint from checking any further, even if it is dereferenced again (medium)