An array length must be a decimal number: long[QWORDS] with a const QWORDS does not parse, and byte[0x40] is 0 #3115

The length of a fixed-size array must be written as a decimal number. A module that names its sizes cannot use those names where the size matters most:

const QWORDS: int = 128 // uint64 lanes per 1024-byte block

fill(mem: long[]) {
    long[QWORDS] scratch     // error[E0100]: Expected NUMBER, got IDENTIFIER
}

struct SkeinCtx {
    ks: long[NW + 1]         // same error
}

So std writes long[128] beside const QWORDS: int = 128, and the two can drift apart. The parser also reads the number with atoi, so a hex length (byte[0x40]) is taken as 0.

Fix: an array length is an integer constant expression: a literal in any base the language accepts, a const of the same file whose value is one, or + - * / % << >> and parentheses over those. This holds in every place a length is written: local declarations, struct fields, parameters, actor state, const tables and make's array forms. A name that is not an integer constant is a compile error saying so, and so is a length that is zero or less. The reference states the rule in Array Types, and the std modules that wrote a number beside a named size use the name.

Found on #3101 (#3107, moving argon2's and skein's scratch buffers onto arrays).