Unit test for constant folding success

General Usage
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6

It relies on repr being invariant under quote interpolation, which may not be the case. For simple cases like integers and floats this works, because these objects are literals & placed into the IR directly, but for more complicated expressions this is no longer the case:

julia> struct Foo
           a::Int
       end

julia> test_constant_folding(() -> Foo(1), Foo(1))
Test Failed at REPL[9]:10
  Expression: repr(only(code)) == repr(:(return $r))
   Evaluated: ":(return \$(QuoteNode(Foo(1))))" == ":(return Foo(1))"

ERROR: There was an error during testing

Even without repr your property doesn’t hold, because interpolation is not in general the same as when a value is constructed by the compiler:

#=
           dump(only(code))
           cmp = :(return $r)
           dump(cmp)
=#
Core.ReturnNode
  val: QuoteNode
    value: Foo
      a: Int64 1
Expr
  head: Symbol return
  args: Array{Any}((1,))
    1: Foo
      a: Int64 1

That’s why I’m saying that the “most blessed” way of doing this is through the constant folding effects/type inference.

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