fix invalid transform on const

[alexlamsl]

• preserve (re)assignment to const for runtime error
• suppress cascade on const, as runtime behaviour is ill-defined

#1500 (comment)

Backport candidate for v2.x

[kzc]

Backport candidate for v2.x

This PR is for master and harmony?

Do you plan to fix this issue and cut a 3.x release before you apply the const removal PR #1910 in 3.x?

[alexlamsl]

This PR will be short-lived on master, but I did it here because both v2.x and harmony would benefit from this patch.

And yes, this will get merged first, then #1910 will be rebased and merged.

[alexlamsl]

@kzc I would be grateful if you can test this PR for all the corner cases you have in mind 😉

[kzc]

Cool. Could you merge this PR first, make a new 3.x release, then merge #1910?

[alexlamsl]

Cool. Could you merge this PR first, make a new 3.x release, then merge #1910?

Sure, I don't mind it either way 👍

[kzc]

I see this PR handles const reassignment and const modification via unary operators - that's all I can think of to test it.