math.simplify reorders operations

[AlexxSurin]

math.simplify('x + y + a', [{l: 'n+-c', r: 'n-c'}], {a: -1}).toString()

gives

"x - 1 + y"

The order of operations gets changed. Is it an issue?
Is there any way to just simplify signs ('+-n' => '-n', '--n' => 'n') without node tree getting rearranged so drastically (and get x + y - 1 in my example)?

[firepick1]

I have no idea why the legacy simplify does what you saw, but I added your sensible simplification to simplifyCore since it can be done in a single pass. I added a new test that replicated your output and fixed it as suggested. I think the optimization is benign since the precedence of binary + and - are the same--but I'm only 98.1% sure. 😄

4787237
e9fa999

[AlexxSurin]

Nice! Thank you!

[firepick1]

@jos will determine next steps.

[josdejong]

This should be fixed now in v3.16.3, thanks @firepick1 !