StackOverflow with operate!! and NonlinearExpr

[blegat]

This should be investigated, I wouldn't expect this to cause a StackOverflow

JuMP.jl/src/mutable_arithmetics.jl

Lines 289 to 291 in a573de2

	# We can't use `operate!!` here because in the IsNotMutable case (e.g.,
	# NonlinearExpr), it will fallback to this method and cause a StackOverflow.
	if _MA.mutability(T) == _MA.IsNotMutable()

[odow]

I think this is expected behavior. See #3106 (comment)

julia> import MutableArithmetics as MA

julia> struct Foo <: MA.AbstractMutable
           x::Int
       end

julia> Base.copy(f::Foo) = Foo(f.x)

julia> function MA.add_mul(lhs::Foo, x::Union{Int,Foo}, y::Union{Int,Foo})
           return MA.operate!!(MA.add_mul, copy(lhs), x, y)
       end

julia> lhs = Foo(2)
Foo(2)

julia> x = Foo(3)
Foo(3)

julia> MA.add_mul(lhs, x, 3)
ERROR: StackOverflowError:
Stacktrace:
     [1] operate_fallback!!(::MutableArithmetics.IsNotMutable, ::typeof(MutableArithmetics.add_mul), ::Foo, ::Foo, ::Int64)
       @ MutableArithmetics ~/.julia/dev/MutableArithmetics/src/interface.jl:581
     [2] operate!!(::typeof(MutableArithmetics.add_mul), ::Foo, ::Foo, ::Int64)
       @ MutableArithmetics ~/.julia/dev/MutableArithmetics/src/rewrite.jl:89
     [3] add_mul(lhs::Foo, x::Foo, y::Int64)
       @ Main ./REPL[26]:2
     [4] operate(op::typeof(MutableArithmetics.add_mul), x::Foo, y::Foo, args::Int64)
       @ MutableArithmetics ~/.julia/dev/MutableArithmetics/src/interface.jl:206
     [5] operate_fallback!!(::MutableArithmetics.IsNotMutable, ::typeof(MutableArithmetics.add_mul), ::Foo, ::Foo, ::Int64)
       @ MutableArithmetics ~/.julia/dev/MutableArithmetics/src/interface.jl:586
--- the last 4 lines are repeated 19994 more times ---
 [79982] operate!!(::typeof(MutableArithmetics.add_mul), ::Foo, ::Foo, ::Int64)
       @ MutableArithmetics ~/.julia/dev/MutableArithmetics/src/rewrite.jl:89
 [79983] add_mul(lhs::Foo, x::Foo, y::Int64)
       @ Main ./REPL[26]:2

[blegat]

Oh sorry I missed that comment. It's good the PR is merged and we can now discuss on separate issue, it's going to be easier to keep track of discussions threads ^^

[odow]

I don't understand what there is to discuss here. This is expected behavior. The definition of add_mul ends up calling the same definition of add_mul, which is a recursive loop.

[odow]

What is there to do here?

[blegat]

I think it's fine, we could add a link to this issue in the comments in the code