Missing Declaration in Struct causes translate-c to Generate Invalid Zig

[Jared-Miller]

Some headers (Windows) use structs with missing declarations. When importing the Windows headers, you can #define NONAMELESSUNION to replace all the nameless unions/structs with dummy values. Discussion in #985, #1214, and #4081 might be relevant to how to implement this.

There are four different cases I tried in Zig:

• No names defined (valid Zig code, but no elements)
• One name defined (valid Zig code with the single named element)
• Unnamed struct as a member (invalid Zig code)
• Nested struct declaration without a name generates (valid Zig code, generated name)

Based on the fourth case, I believe that the previous three should all be generating unnamed elements instead of excluding them to be consistent. One of the referenced issues mentions that Zig can re-order the struct contents, so it may not be that simple to maintain compatibility.

No names defined generates valid Zig code with no elements:

typedef struct NONAMES
{
    int;
    long;
} NONAMES;

pub const struct_NONAMES = extern struct {};
pub const NONAMES = struct_NONAMES;

One name generates valid Zig code with the single named element:

typedef struct ONENAME
{
    int;
    long b;
} ONENAME;

pub const struct_ONENAME = extern struct {
    b: c_long,
};
pub const ONENAME = struct_ONENAME;

With an unnamed struct, invalid Zig code is generated.

typedef struct NAMED
{
    long name;
} NAMED;

typedef struct ONENAMEWITHSTRUCT
{
    NAMED;
    long b;
} ONENAMEWITHSTRUCT;

pub const struct_NAMED = extern struct {
    name: c_long,
};
pub const NAMED = struct_NAMED;
pub const struct_ONENAMEWITHSTRUCT = extern struct {
    : struct_NAMED,
    b: c_long,
};

A nested struct declaration without a name generates valid Zig code:

typedef struct ONENAMEWITHSTRUCT
{
    struct {
        long name;
    };
    long b;
} ONENAMEWITHSTRUCT;

const struct_unnamed_2 = extern struct {
    name: c_long,
};
pub const struct_ONENAMEWITHSTRUCT = extern struct {
    unnamed_1: struct_unnamed_2,
    b: c_long,
};

[Jared-Miller]

Also related to #3453