bun.sh/src/meta.zig

const std = @import("std");
const bun = @import("root").bun;

pub fn OptionalChild(comptime T: type) type {
    const tyinfo = @typeInfo(T);
    if (tyinfo != .pointer) @compileError("OptionalChild(T) requires that T be a pointer to an optional type.");
    const child = @typeInfo(tyinfo.pointer.child);
    if (child != .Optional) @compileError("OptionalChild(T) requires that T be a pointer to an optional type.");
    return child.Optional.child;
}

pub fn EnumFields(comptime T: type) []const std.builtin.Type.EnumField {
    const tyinfo = @typeInfo(T);
    return switch (tyinfo) {
        .@"union" => std.meta.fields(tyinfo.@"union".tag_type.?),
        .@"enum" => tyinfo.@"enum".fields,
        else => {
            @compileError("Used `EnumFields(T)` on a type that is not an `enum` or a `union(enum)`");
        },
    };
}

pub fn ReturnOfMaybe(comptime function: anytype) type {
    const Func = @TypeOf(function);
    const typeinfo: std.builtin.Type.Fn = @typeInfo(Func).@"fn";
    const MaybeType = typeinfo.return_type orelse @compileError("Expected the function to have a return type");
    return MaybeResult(MaybeType);
}

pub fn MaybeResult(comptime MaybeType: type) type {
    const maybe_ty_info = @typeInfo(MaybeType);

    const maybe = maybe_ty_info.@"union";
    if (maybe.fields.len != 2) @compileError("Expected the Maybe type to be a union(enum) with two variants");

    if (!std.mem.eql(u8, maybe.fields[0].name, "err")) {
        @compileError("Expected the first field of the Maybe type to be \"err\", got: " ++ maybe.fields[0].name);
    }

    if (!std.mem.eql(u8, maybe.fields[1].name, "result")) {
        @compileError("Expected the second field of the Maybe type to be \"result\"" ++ maybe.fields[1].name);
    }

    return maybe.fields[1].type;
}

pub fn ReturnOf(comptime function: anytype) type {
    return ReturnOfType(@TypeOf(function));
}

pub fn ReturnOfType(comptime Type: type) type {
    const typeinfo: std.builtin.Type.Fn = @typeInfo(Type).@"fn";
    return typeinfo.return_type orelse void;
}

pub fn typeName(comptime Type: type) []const u8 {
    const name = @typeName(Type);
    return typeBaseName(name);
}

/// partially emulates behaviour of @typeName in previous Zig versions,
/// converting "some.namespace.MyType" to "MyType"
pub inline fn typeBaseName(comptime fullname: [:0]const u8) [:0]const u8 {
    @setEvalBranchQuota(1_000_000);
    // leave type name like "namespace.WrapperType(namespace.MyType)" as it is
    const baseidx = comptime std.mem.indexOf(u8, fullname, "(");
    if (baseidx != null) return comptime fullname;

    const idx = comptime std.mem.lastIndexOf(u8, fullname, ".");

    const name = if (idx == null) fullname else fullname[(idx.? + 1)..];
    return comptime name;
}

pub fn enumFieldNames(comptime Type: type) []const []const u8 {
    var names: [std.meta.fields(Type).len][]const u8 = std.meta.fieldNames(Type).*;
    var i: usize = 0;
    for (names) |name| {
        // zig seems to include "_" or an empty string in the list of enum field names
        // it makes sense, but humans don't want that
        if (bun.strings.eqlAnyComptime(name, &.{ "_none", "", "_" })) {
            continue;
        }
        names[i] = name;
        i += 1;
    }
    return names[0..i];
}

pub fn banFieldType(comptime Container: type, comptime T: type) void {
    comptime {
        for (std.meta.fields(Container)) |field| {
            if (field.type == T) {
                @compileError(std.fmt.comptimePrint(typeName(T) ++ " field \"" ++ field.name ++ "\" not allowed in " ++ typeName(Container), .{}));
            }
        }
    }
}

// []T -> T
// *const T -> T
// *[n]T -> T
pub fn Item(comptime T: type) type {
    switch (@typeInfo(T)) {
        .pointer => |ptr| {
            if (ptr.size == .one) {
                switch (@typeInfo(ptr.child)) {
                    .array => |array| {
                        return array.child;
                    },
                    else => {},
                }
            }
            return ptr.child;
        },
        else => return std.meta.Child(T),
    }
}

/// Returns .{a, ...args_}
pub fn ConcatArgs1(
    comptime func: anytype,
    a: anytype,
    args_: anytype,
) std.meta.ArgsTuple(@TypeOf(func)) {
    var args: std.meta.ArgsTuple(@TypeOf(func)) = undefined;
    args[0] = a;

    inline for (args_, 1..) |arg, i| {
        args[i] = arg;
    }

    return args;
}

/// Returns .{a, b, ...args_}
pub inline fn ConcatArgs2(
    comptime func: anytype,
    a: anytype,
    b: anytype,
    args_: anytype,
) std.meta.ArgsTuple(@TypeOf(func)) {
    var args: std.meta.ArgsTuple(@TypeOf(func)) = undefined;
    args[0] = a;
    args[1] = b;

    inline for (args_, 2..) |arg, i| {
        args[i] = arg;
    }

    return args;
}

/// Returns .{a, b, c, d, ...args_}
pub inline fn ConcatArgs4(
    comptime func: anytype,
    a: anytype,
    b: anytype,
    c: anytype,
    d: anytype,
    args_: anytype,
) std.meta.ArgsTuple(@TypeOf(func)) {
    var args: std.meta.ArgsTuple(@TypeOf(func)) = undefined;
    args[0] = a;
    args[1] = b;
    args[2] = c;
    args[3] = d;

    inline for (args_, 4..) |arg, i| {
        args[i] = arg;
    }

    return args;
}

// Copied from std.meta
fn CreateUniqueTuple(comptime N: comptime_int, comptime types: [N]type) type {
    var tuple_fields: [types.len]std.builtin.Type.StructField = undefined;
    inline for (types, 0..) |T, i| {
        @setEvalBranchQuota(10_000);
        var num_buf: [128]u8 = undefined;
        tuple_fields[i] = .{
            .name = std.fmt.bufPrintZ(&num_buf, "{d}", .{i}) catch unreachable,
            .type = T,
            .default_value_ptr = null,
            .is_comptime = false,
            .alignment = if (@sizeOf(T) > 0) @alignOf(T) else 0,
        };
    }

    return @Type(.{
        .@"struct" = .{
            .is_tuple = true,
            .layout = .auto,
            .decls = &.{},
            .fields = &tuple_fields,
        },
    });
}

pub fn hasStableMemoryLayout(comptime T: type) bool {
    const tyinfo = @typeInfo(T);
    return switch (tyinfo) {
        .Type => true,
        .Void => true,
        .Bool => true,
        .Int => true,
        .Float => true,
        .@"enum" => {
            // not supporting this rn
            if (tyinfo.@"enum".is_exhaustive) return false;
            return hasStableMemoryLayout(tyinfo.@"enum".tag_type);
        },
        .@"struct" => switch (tyinfo.@"struct".layout) {
            .auto => {
                inline for (tyinfo.@"struct".fields) |field| {
                    if (!hasStableMemoryLayout(field.field_type)) return false;
                }
                return true;
            },
            .@"extern" => true,
            .@"packed" => false,
        },
        .@"union" => switch (tyinfo.@"union".layout) {
            .auto => {
                if (tyinfo.@"union".tag_type == null or !hasStableMemoryLayout(tyinfo.@"union".tag_type.?)) return false;

                inline for (tyinfo.@"union".fields) |field| {
                    if (!hasStableMemoryLayout(field.type)) return false;
                }

                return true;
            },
            .@"extern" => true,
            .@"packed" => false,
        },
        else => true,
    };
}

pub fn isSimpleCopyType(comptime T: type) bool {
    @setEvalBranchQuota(1_000_000);
    const tyinfo = @typeInfo(T);
    return switch (tyinfo) {
        .void => true,
        .bool => true,
        .int => true,
        .float => true,
        .@"enum" => true,
        .@"struct" => {
            inline for (tyinfo.@"struct".fields) |field| {
                if (!isSimpleCopyType(field.type)) return false;
            }
            return true;
        },
        .@"union" => {
            inline for (tyinfo.@"union".fields) |field| {
                if (!isSimpleCopyType(field.type)) return false;
            }
            return true;
        },
        .optional => return isSimpleCopyType(tyinfo.optional.child),
        else => false,
    };
}

pub fn isScalar(comptime T: type) bool {
    return switch (T) {
        i32, u32, i64, u64, f32, f64, bool => true,
        else => {
            const tyinfo = @typeInfo(T);
            if (tyinfo == .@"enum") return true;
            return false;
        },
    };
}

pub fn isSimpleEqlType(comptime T: type) bool {
    const tyinfo = @typeInfo(T);
    return switch (tyinfo) {
        .type => true,
        .void => true,
        .bool => true,
        .int => true,
        .float => true,
        .@"enum" => true,
        else => false,
    };
}

pub const ListContainerType = enum {
    array_list,
    baby_list,
    small_list,
};
pub fn looksLikeListContainerType(comptime T: type) ?struct { list: ListContainerType, child: type } {
    const tyinfo = @typeInfo(T);
    if (tyinfo == .@"struct") {
        // Looks like array list
        if (tyinfo.@"struct".fields.len == 2 and
            std.mem.eql(u8, tyinfo.@"struct".fields[0].name, "items") and
            std.mem.eql(u8, tyinfo.@"struct".fields[1].name, "capacity"))
            return .{ .list = .array_list, .child = std.meta.Child(tyinfo.@"struct".fields[0].type) };

        // Looks like babylist
        if (tyinfo.@"struct".fields.len == 3 and
            std.mem.eql(u8, tyinfo.@"struct".fields[0].name, "ptr") and
            std.mem.eql(u8, tyinfo.@"struct".fields[1].name, "len") and
            std.mem.eql(u8, tyinfo.@"struct".fields[2].name, "cap"))
            return .{ .list = .baby_list, .child = std.meta.Child(tyinfo.@"struct".fields[0].type) };

        // Looks like SmallList
        if (tyinfo.@"struct".fields.len == 2 and
            std.mem.eql(u8, tyinfo.@"struct".fields[0].name, "capacity") and
            std.mem.eql(u8, tyinfo.@"struct".fields[1].name, "data")) return .{
            .list = .small_list,
            .child = std.meta.Child(
                @typeInfo(tyinfo.@"struct".fields[1].type).@"union".fields[0].type,
            ),
        };
    }

    return null;
}

pub fn Tagged(comptime U: type, comptime T: type) type {
    var info: std.builtin.Type.Union = @typeInfo(U).@"union";
    info.tag_type = T;
    info.decls = &.{};
    return @Type(.{ .@"union" = info });
}