AssertIsLessOrEqual panics when first argument is an int literal

[akirillo]

One of my circuits attempts to do the following:

api.AssertIsLessOrEqual(0, v)

But when I try to test this, it panics with the message:

interface conversion: frontend.Variable is uint, not expr.LinearExpression

Exact message depends on the way the circuit is compiled (e.g. r1cs or scs, groth16 or plonk, which curve, etc), e.g. may say:

interface conversion: frontend.Variable is int, not expr.TermToRefactor

---

For (R1CS, Groth16, BN254), I tracked this down to the mustBeLessOrEqVar function in frontend/cs/r1cs/api_assertions.go, on line 131, where we attempt to do a type assertion of aBits[i].(expr.LinearExpression). When I was debugging this, it seemed that aBits[i] was a frontend.Variable wrapped around a uint, not a expr.LinearExpression.

Please let me know what other info I can provide to help with this, I'm not much of a Go guru so I'm not sure why this type assertion is failing, or what the fix should be

[akirillo]

@gbotrel Should we close this since #511 got merged, or only when it makes it to the next release?