Exposing a constants requires to expose all constants in subexpression

[FriedrichGretz]

Describe the bug This code

module exposes C

const A: nat8 = 4
const B: nat8 = 18 
const C = A * (B - 2)

fails to compile with the error message that B (and A) is less accessible than C. However const expressions can be evaluated at compile time and so only the value 64 needs to be written to the signature not how it is calculated in the module.

Expected behaviour Above code should compile without errors.

Additional context Currently, const in Blech declares a compile time constant (aka #define) in C. If that changes due to complex types than the issue above might become more intricate.

[schorg]

This is not a bug - its a feature by design:

• Consts are regarded as transparent - they expose their internal structure, like a transparent type.
• Consts are compile time values - constant evaluation is an optimization.
• Not all consts can be evaluated at compile time - e. g. extern const
• All compile time values need to expose their internal structure in the signature - imagine compile-time functions, generic functions that must be monomorphised - in order to allow compile-time evaluation in the importing module.
• Compile-time evaluation should not change signatures.

These considerations lead to the decision to make signature generation purely syntactic, not taking into account typing and constant evaluation.