There are four methods with @assume_effects :total applied to the entire method in base/irrationals.jl:

Issues:

• The :total effect is too powerful and not future-proof. I guess what's actually desired is just :foldable.
• It's not valid to apply @assume_effects to the ::AbstractIrrational methods, because users may define custom subtypes of AbstractIrrational, and thus calls like BigFloat(::AbstractIrrational) or big(::AbstractIrrational) may execute arbitrary code. That said ...
• It's not valid to apply @assume_effects even just for ::Irrational, because users may define custom subtypes of Irrational! Example:

# in a user package
struct IrrationalSymbol end
function big(::Irrational{IrrationalSymbol})
    execute_arbitrary_code()
end

This seems perfectly legal, or at least it's not type piracy.

The solution seems simple: define a Union of all known irrational constants, something like the following, then dispatch on it for methods that have @assume_effects, instead of on AbstractIrrational or on Irrational:

const _KnownIrrational = (ℯ, π, MathConstants.γ, MathConstants.catalan, MathConstants.φ)

This will ensure calls involving the known constants are foldable, and allow the unsafe @assume_effects annotations to be deleted. Will make a PR later.