go/types: constant values should reported as machine values for concrete types

[griesemer]

Feature request: The reported values of constants should be the respective machine
values (perhaps in addition to the precise values) if the constant type is not an
untyped type.

[griesemer]

Proposal:

// TypeAndValue reports the type and value (for constants)
// of the corresponding expression. If the constant is used in
// an expression at run time (for instance in an assignment),
// GoValue contains the corresponding machine (materialized)
// value. The type of GoValue is the underlying type of the
// constant (a Go basic type permissible as constant type).
type TypeAndValue struct {
    mode  operandMode
    Type  Type
    Value constant.Value
    GoValue interface{}
}

[rsc]

Too late for Go 1.6.

[griesemer]

Nice to have. Not for 1.10.

[griesemer]

Not urgent. Moving to 1.12.