flecs-zig-ble/src/meta.zig

//! Since the `std.meta.trait` module was removed from Zig's standard
//! library, we're re-introducing some of the functions we needed.

const std = @import("std");

/// Returns if the provided type is a tuple.
pub fn isTuple(comptime T: type) bool {
    return @typeInfo(T) == .Struct and @typeInfo(T).Struct.is_tuple;
}

/// Returns true if the passed type will coerce to []const u8.
/// Any of the following are considered strings:
/// ```
/// []const u8, [:S]const u8, *const [N]u8, *const [N:S]u8,
/// []u8, [:S]u8, *[:S]u8, *[N:S]u8.
/// ```
/// These types are not considered strings:
/// ```
/// u8, [N]u8, [*]const u8, [*:0]const u8,
/// [*]const [N]u8, []const u16, []const i8,
/// *const u8, ?[]const u8, ?*const [N]u8.
/// ```
pub fn isZigString(comptime T: type) bool {
    return comptime blk: {
        // Only pointer types can be strings, no optionals
        const info = @typeInfo(T);
        if (info != .Pointer) break :blk false;

        const ptr = &info.Pointer;
        // Check for CV qualifiers that would prevent coerction to []const u8
        if (ptr.is_volatile or ptr.is_allowzero) break :blk false;

        // If it's already a slice, simple check.
        if (ptr.size == .Slice) {
            break :blk ptr.child == u8;
        }

        // Otherwise check if it's an array type that coerces to slice.
        if (ptr.size == .One) {
            const child = @typeInfo(ptr.child);
            if (child == .Array) {
                const arr = &child.Array;
                break :blk arr.child == u8;
            }
        }

        break :blk false;
    };
}

/// Returns the type of the specified expression, which must be either
/// just a `type`, or a tuple in the form of `.{ TRelation, TTarget }`,
/// representing a relationship pair in Flecs.
///
/// If the expression is a pair, the type is determined like this:
/// - If `TRelation` is a non-zero-sized type, it is returned.
/// - If `TTarget` is a non-zero-sized type, it is returned.
/// - Otherwise, a compile error is raised.
pub fn AnyToType(comptime expr: anytype) type {
    switch (@typeInfo(@TypeOf(expr))) {
        .Type => return expr,
        .Struct => |s| {
            if (!s.is_tuple or s.fields.len != 2)
                @compileError("Expression must be a type or a tuple of two types");

            const TRelation = expr[0];
            const TTarget = expr[1];
            if (@TypeOf(TRelation) != type) @compileError("TRelation must be a type, but is " ++ @typeName(@TypeOf(TRelation)));
            if (@TypeOf(TTarget) != type) @compileError("TTarget must be a type, but is " ++ @typeName(@TypeOf(TTarget)));

            if (@sizeOf(TRelation) > 0) return TRelation;
            if (@sizeOf(TTarget) > 0) return TTarget;
            @compileError("Either TRelation or TTarget must be a non-zero-sized type");
        },
        else => @compileError("Expression must be a type or a tuple of two types"),
    }
}

/// Gets the simplified type name of the specified type.
/// That is, without any namespace qualifiers.
pub fn simpleTypeName(comptime T: type) [:0]const u8 {
    const fullName = @typeName(T);
    const index = std.mem.lastIndexOf(u8, fullName, ".");
    return if (index) |i| fullName[(i + 1)..] else fullName;
}