struct Serializer [src]

Alias for std.zon.Serializer
Lower level control over serialization, you can create a new instance with serializer. Useful when you want control over which fields are serialized, how they're represented, or want to write a ZON object that does not exist in memory. You can serialize values with value. To serialize recursive types, the following are provided: valueMaxDepth valueArbitraryDepth You can also serialize values using specific notations: int float codePoint tuple tupleMaxDepth tupleArbitraryDepth string multilineString For manual serialization of containers, see: beginStruct beginTuple
Fields

options: Options = .{}
indent_level: u8 = 0
writer: *Writer
Members

beginStruct (Function)
beginTuple (Function)
codePoint (Function)
CodePointError (Error Set)
ContainerOptions (struct)
DepthError (Error Set)
EmitCodepointLiterals (enum)
Error (Error Set)
float (Function)
ident (Function)
int (Function)
multilineString (Function)
MultilineStringError (Error Set)
MultilineStringOptions (struct)
Options (struct)
string (Function)
Struct (struct)
tuple (Function)
Tuple (struct)
tupleArbitraryDepth (Function)
tupleMaxDepth (Function)
value (Function)
valueArbitraryDepth (Function)
valueMaxDepth (Function)
ValueOptions (struct)
Source

  //! Lower level control over serialization, you can create a new instance with `serializer`.
//!
//! Useful when you want control over which fields are serialized, how they're represented,
//! or want to write a ZON object that does not exist in memory.
//!
//! You can serialize values with `value`. To serialize recursive types, the following are provided:
//! * `valueMaxDepth`
//! * `valueArbitraryDepth`
//!
//! You can also serialize values using specific notations:
//! * `int`
//! * `float`
//! * `codePoint`
//! * `tuple`
//! * `tupleMaxDepth`
//! * `tupleArbitraryDepth`
//! * `string`
//! * `multilineString`
//!
//! For manual serialization of containers, see:
//! * `beginStruct`
//! * `beginTuple`

options: Options = .{},
indent_level: u8 = 0,
writer: *Writer,

const Serializer = @This();
const std = @import("std");
const assert = std.debug.assert;
const Writer = std.Io.Writer;

pub const Error = Writer.Error;
pub const DepthError = Error || error{ExceededMaxDepth};

pub const Options = struct {
    /// If false, only syntactically necessary whitespace is emitted.
    whitespace: bool = true,
};

/// Options for manual serialization of container types.
pub const ContainerOptions = struct {
    /// The whitespace style that should be used for this container. Ignored if whitespace is off.
    whitespace_style: union(enum) {
        /// If true, wrap every field. If false do not.
        wrap: bool,
        /// Automatically decide whether to wrap or not based on the number of fields. Following
        /// the standard rule of thumb, containers with more than two fields are wrapped.
        fields: usize,
    } = .{ .wrap = true },

    fn shouldWrap(self: ContainerOptions) bool {
        return switch (self.whitespace_style) {
            .wrap => |wrap| wrap,
            .fields => |fields| fields > 2,
        };
    }
};

/// Options for serialization of an individual value.
///
/// See `SerializeOptions` for more information on these options.
pub const ValueOptions = struct {
    emit_codepoint_literals: EmitCodepointLiterals = .never,
    emit_strings_as_containers: bool = false,
    emit_default_optional_fields: bool = true,
};

/// Determines when to emit Unicode code point literals as opposed to integer literals.
pub const EmitCodepointLiterals = enum {
    /// Never emit Unicode code point literals.
    never,
    /// Emit Unicode code point literals for any `u8` in the printable ASCII range.
    printable_ascii,
    /// Emit Unicode code point literals for any unsigned integer with 21 bits or fewer
    /// whose value is a valid non-surrogate code point.
    always,

    /// If the value should be emitted as a Unicode codepoint, return it as a u21.
    fn emitAsCodepoint(self: @This(), val: anytype) ?u21 {
        // Rule out incompatible integer types
        switch (@typeInfo(@TypeOf(val))) {
            .int => |int_info| if (int_info.signedness == .signed or int_info.bits > 21) {
                return null;
            },
            .comptime_int => {},
            else => comptime unreachable,
        }

        // Return null if the value shouldn't be printed as a Unicode codepoint, or the value casted
        // to a u21 if it should.
        switch (self) {
            .always => {
                const c = std.math.cast(u21, val) orelse return null;
                if (!std.unicode.utf8ValidCodepoint(c)) return null;
                return c;
            },
            .printable_ascii => {
                const c = std.math.cast(u8, val) orelse return null;
                if (!std.ascii.isPrint(c)) return null;
                return c;
            },
            .never => {
                return null;
            },
        }
    }
};

/// Serialize a value, similar to `serialize`.
pub fn value(self: *Serializer, val: anytype, options: ValueOptions) Error!void {
    comptime assert(!typeIsRecursive(@TypeOf(val)));
    return self.valueArbitraryDepth(val, options);
}

/// Serialize a value, similar to `serializeMaxDepth`.
/// Can return `error.ExceededMaxDepth`.
pub fn valueMaxDepth(self: *Serializer, val: anytype, options: ValueOptions, depth: usize) DepthError!void {
    try checkValueDepth(val, depth);
    return self.valueArbitraryDepth(val, options);
}

/// Serialize a value, similar to `serializeArbitraryDepth`.
pub fn valueArbitraryDepth(self: *Serializer, val: anytype, options: ValueOptions) Error!void {
    comptime assert(canSerializeType(@TypeOf(val)));
    switch (@typeInfo(@TypeOf(val))) {
        .int, .comptime_int => if (options.emit_codepoint_literals.emitAsCodepoint(val)) |c| {
            self.codePoint(c) catch |err| switch (err) {
                error.InvalidCodepoint => unreachable, // Already validated
                else => |e| return e,
            };
        } else {
            try self.int(val);
        },
        .float, .comptime_float => try self.float(val),
        .bool, .null => try self.writer.print("{}", .{val}),
        .enum_literal => try self.ident(@tagName(val)),
        .@"enum" => try self.ident(@tagName(val)),
        .pointer => |pointer| {
            // Try to serialize as a string
            const item: ?type = switch (@typeInfo(pointer.child)) {
                .array => |array| array.child,
                else => if (pointer.size == .slice) pointer.child else null,
            };
            if (item == u8 and
                (pointer.sentinel() == null or pointer.sentinel() == 0) and
                !options.emit_strings_as_containers)
            {
                return try self.string(val);
            }

            // Serialize as either a tuple or as the child type
            switch (pointer.size) {
                .slice => try self.tupleImpl(val, options),
                .one => try self.valueArbitraryDepth(val.*, options),
                else => comptime unreachable,
            }
        },
        .array => {
            var container = try self.beginTuple(
                .{ .whitespace_style = .{ .fields = val.len } },
            );
            for (val) |item_val| {
                try container.fieldArbitraryDepth(item_val, options);
            }
            try container.end();
        },
        .@"struct" => |@"struct"| if (@"struct".is_tuple) {
            var container = try self.beginTuple(
                .{ .whitespace_style = .{ .fields = @"struct".fields.len } },
            );
            inline for (val) |field_value| {
                try container.fieldArbitraryDepth(field_value, options);
            }
            try container.end();
        } else {
            // Decide which fields to emit
            const fields, const skipped: [@"struct".fields.len]bool = if (options.emit_default_optional_fields) b: {
                break :b .{ @"struct".fields.len, @splat(false) };
            } else b: {
                var fields = @"struct".fields.len;
                var skipped: [@"struct".fields.len]bool = @splat(false);
                inline for (@"struct".fields, &skipped) |field_info, *skip| {
                    if (field_info.default_value_ptr) |ptr| {
                        const default: *const field_info.type = @ptrCast(@alignCast(ptr));
                        const field_value = @field(val, field_info.name);
                        if (std.meta.eql(field_value, default.*)) {
                            skip.* = true;
                            fields -= 1;
                        }
                    }
                }
                break :b .{ fields, skipped };
            };

            // Emit those fields
            var container = try self.beginStruct(
                .{ .whitespace_style = .{ .fields = fields } },
            );
            inline for (@"struct".fields, skipped) |field_info, skip| {
                if (!skip) {
                    try container.fieldArbitraryDepth(
                        field_info.name,
                        @field(val, field_info.name),
                        options,
                    );
                }
            }
            try container.end();
        },
        .@"union" => |@"union"| {
            comptime assert(@"union".tag_type != null);
            switch (val) {
                inline else => |pl, tag| if (@TypeOf(pl) == void)
                    try self.writer.print(".{s}", .{@tagName(tag)})
                else {
                    var container = try self.beginStruct(.{ .whitespace_style = .{ .fields = 1 } });

                    try container.fieldArbitraryDepth(
                        @tagName(tag),
                        pl,
                        options,
                    );

                    try container.end();
                },
            }
        },
        .optional => if (val) |inner| {
            try self.valueArbitraryDepth(inner, options);
        } else {
            try self.writer.writeAll("null");
        },
        .vector => |vector| {
            var container = try self.beginTuple(
                .{ .whitespace_style = .{ .fields = vector.len } },
            );
            for (0..vector.len) |i| {
                try container.fieldArbitraryDepth(val[i], options);
            }
            try container.end();
        },

        else => comptime unreachable,
    }
}

/// Serialize an integer.
pub fn int(self: *Serializer, val: anytype) Error!void {
    try self.writer.printInt(val, 10, .lower, .{});
}

/// Serialize a float.
pub fn float(self: *Serializer, val: anytype) Error!void {
    switch (@typeInfo(@TypeOf(val))) {
        .float => if (std.math.isNan(val)) {
            return self.writer.writeAll("nan");
        } else if (std.math.isPositiveInf(val)) {
            return self.writer.writeAll("inf");
        } else if (std.math.isNegativeInf(val)) {
            return self.writer.writeAll("-inf");
        } else if (std.math.isNegativeZero(val)) {
            return self.writer.writeAll("-0.0");
        } else {
            try self.writer.print("{d}", .{val});
        },
        .comptime_float => if (val == 0) {
            return self.writer.writeAll("0");
        } else {
            try self.writer.print("{d}", .{val});
        },
        else => comptime unreachable,
    }
}

/// Serialize `name` as an identifier prefixed with `.`.
///
/// Escapes the identifier if necessary.
pub fn ident(self: *Serializer, name: []const u8) Error!void {
    try self.writer.print(".{f}", .{std.zig.fmtIdPU(name)});
}

pub const CodePointError = Error || error{InvalidCodepoint};

/// Serialize `val` as a Unicode codepoint.
///
/// Returns `error.InvalidCodepoint` if `val` is not a valid Unicode codepoint.
pub fn codePoint(self: *Serializer, val: u21) CodePointError!void {
    try self.writer.print("'{f}'", .{std.zig.fmtChar(val)});
}

/// Like `value`, but always serializes `val` as a tuple.
///
/// Will fail at comptime if `val` is not a tuple, array, pointer to an array, or slice.
pub fn tuple(self: *Serializer, val: anytype, options: ValueOptions) Error!void {
    comptime assert(!typeIsRecursive(@TypeOf(val)));
    try self.tupleArbitraryDepth(val, options);
}

/// Like `tuple`, but recursive types are allowed.
///
/// Returns `error.ExceededMaxDepth` if `depth` is exceeded.
pub fn tupleMaxDepth(
    self: *Serializer,
    val: anytype,
    options: ValueOptions,
    depth: usize,
) DepthError!void {
    try checkValueDepth(val, depth);
    try self.tupleArbitraryDepth(val, options);
}

/// Like `tuple`, but recursive types are allowed.
///
/// It is the caller's responsibility to ensure that `val` does not contain cycles.
pub fn tupleArbitraryDepth(
    self: *Serializer,
    val: anytype,
    options: ValueOptions,
) Error!void {
    try self.tupleImpl(val, options);
}

fn tupleImpl(self: *Serializer, val: anytype, options: ValueOptions) Error!void {
    comptime assert(canSerializeType(@TypeOf(val)));
    switch (@typeInfo(@TypeOf(val))) {
        .@"struct" => {
            var container = try self.beginTuple(.{ .whitespace_style = .{ .fields = val.len } });
            inline for (val) |item_val| {
                try container.fieldArbitraryDepth(item_val, options);
            }
            try container.end();
        },
        .pointer, .array => {
            var container = try self.beginTuple(.{ .whitespace_style = .{ .fields = val.len } });
            for (val) |item_val| {
                try container.fieldArbitraryDepth(item_val, options);
            }
            try container.end();
        },
        else => comptime unreachable,
    }
}

/// Like `value`, but always serializes `val` as a string.
pub fn string(self: *Serializer, val: []const u8) Error!void {
    try self.writer.print("\"{f}\"", .{std.zig.fmtString(val)});
}

/// Options for formatting multiline strings.
pub const MultilineStringOptions = struct {
    /// If top level is true, whitespace before and after the multiline string is elided.
    /// If it is true, a newline is printed, then the value, followed by a newline, and if
    /// whitespace is true any necessary indentation follows.
    top_level: bool = false,
};

pub const MultilineStringError = Error || error{InnerCarriageReturn};

/// Like `value`, but always serializes to a multiline string literal.
///
/// Returns `error.InnerCarriageReturn` if `val` contains a CR not followed by a newline,
/// since multiline strings cannot represent CR without a following newline.
pub fn multilineString(
    self: *Serializer,
    val: []const u8,
    options: MultilineStringOptions,
) MultilineStringError!void {
    // Make sure the string does not contain any carriage returns not followed by a newline
    var i: usize = 0;
    while (i < val.len) : (i += 1) {
        if (val[i] == '\r') {
            if (i + 1 < val.len) {
                if (val[i + 1] == '\n') {
                    i += 1;
                    continue;
                }
            }
            return error.InnerCarriageReturn;
        }
    }

    if (!options.top_level) {
        try self.newline();
        try self.indent();
    }

    try self.writer.writeAll("\\\\");
    for (val) |c| {
        if (c != '\r') {
            try self.writer.writeByte(c); // We write newlines here even if whitespace off
            if (c == '\n') {
                try self.indent();
                try self.writer.writeAll("\\\\");
            }
        }
    }

    if (!options.top_level) {
        try self.writer.writeByte('\n'); // Even if whitespace off
        try self.indent();
    }
}

/// Create a `Struct` for writing ZON structs field by field.
pub fn beginStruct(self: *Serializer, options: ContainerOptions) Error!Struct {
    return Struct.begin(self, options);
}

/// Creates a `Tuple` for writing ZON tuples field by field.
pub fn beginTuple(self: *Serializer, options: ContainerOptions) Error!Tuple {
    return Tuple.begin(self, options);
}

fn indent(self: *Serializer) Error!void {
    if (self.options.whitespace) {
        try self.writer.splatByteAll(' ', 4 * self.indent_level);
    }
}

fn newline(self: *Serializer) Error!void {
    if (self.options.whitespace) {
        try self.writer.writeByte('\n');
    }
}

fn newlineOrSpace(self: *Serializer, len: usize) Error!void {
    if (self.containerShouldWrap(len)) {
        try self.newline();
    } else {
        try self.space();
    }
}

fn space(self: *Serializer) Error!void {
    if (self.options.whitespace) {
        try self.writer.writeByte(' ');
    }
}

/// Writes ZON tuples field by field.
pub const Tuple = struct {
    container: Container,

    fn begin(parent: *Serializer, options: ContainerOptions) Error!Tuple {
        return .{
            .container = try Container.begin(parent, .anon, options),
        };
    }

    /// Finishes serializing the tuple.
    ///
    /// Prints a trailing comma as configured when appropriate, and the closing bracket.
    pub fn end(self: *Tuple) Error!void {
        try self.container.end();
        self.* = undefined;
    }

    /// Serialize a field. Equivalent to calling `fieldPrefix` followed by `value`.
    pub fn field(
        self: *Tuple,
        val: anytype,
        options: ValueOptions,
    ) Error!void {
        try self.container.field(null, val, options);
    }

    /// Serialize a field. Equivalent to calling `fieldPrefix` followed by `valueMaxDepth`.
    /// Returns `error.ExceededMaxDepth` if `depth` is exceeded.
    pub fn fieldMaxDepth(
        self: *Tuple,
        val: anytype,
        options: ValueOptions,
        depth: usize,
    ) DepthError!void {
        try self.container.fieldMaxDepth(null, val, options, depth);
    }

    /// Serialize a field. Equivalent to calling `fieldPrefix` followed by
    /// `valueArbitraryDepth`.
    pub fn fieldArbitraryDepth(
        self: *Tuple,
        val: anytype,
        options: ValueOptions,
    ) Error!void {
        try self.container.fieldArbitraryDepth(null, val, options);
    }

    /// Starts a field with a struct as a value. Returns the struct.
    pub fn beginStructField(
        self: *Tuple,
        options: ContainerOptions,
    ) Error!Struct {
        try self.fieldPrefix();
        return self.container.serializer.beginStruct(options);
    }

    /// Starts a field with a tuple as a value. Returns the tuple.
    pub fn beginTupleField(
        self: *Tuple,
        options: ContainerOptions,
    ) Error!Tuple {
        try self.fieldPrefix();
        return self.container.serializer.beginTuple(options);
    }

    /// Print a field prefix. This prints any necessary commas, and whitespace as
    /// configured. Useful if you want to serialize the field value yourself.
    pub fn fieldPrefix(self: *Tuple) Error!void {
        try self.container.fieldPrefix(null);
    }
};

/// Writes ZON structs field by field.
pub const Struct = struct {
    container: Container,

    fn begin(parent: *Serializer, options: ContainerOptions) Error!Struct {
        return .{
            .container = try Container.begin(parent, .named, options),
        };
    }

    /// Finishes serializing the struct.
    ///
    /// Prints a trailing comma as configured when appropriate, and the closing bracket.
    pub fn end(self: *Struct) Error!void {
        try self.container.end();
        self.* = undefined;
    }

    /// Serialize a field. Equivalent to calling `fieldPrefix` followed by `value`.
    pub fn field(
        self: *Struct,
        name: []const u8,
        val: anytype,
        options: ValueOptions,
    ) Error!void {
        try self.container.field(name, val, options);
    }

    /// Serialize a field. Equivalent to calling `fieldPrefix` followed by `valueMaxDepth`.
    /// Returns `error.ExceededMaxDepth` if `depth` is exceeded.
    pub fn fieldMaxDepth(
        self: *Struct,
        name: []const u8,
        val: anytype,
        options: ValueOptions,
        depth: usize,
    ) DepthError!void {
        try self.container.fieldMaxDepth(name, val, options, depth);
    }

    /// Serialize a field. Equivalent to calling `fieldPrefix` followed by
    /// `valueArbitraryDepth`.
    pub fn fieldArbitraryDepth(
        self: *Struct,
        name: []const u8,
        val: anytype,
        options: ValueOptions,
    ) Error!void {
        try self.container.fieldArbitraryDepth(name, val, options);
    }

    /// Starts a field with a struct as a value. Returns the struct.
    pub fn beginStructField(
        self: *Struct,
        name: []const u8,
        options: ContainerOptions,
    ) Error!Struct {
        try self.fieldPrefix(name);
        return self.container.serializer.beginStruct(options);
    }

    /// Starts a field with a tuple as a value. Returns the tuple.
    pub fn beginTupleField(
        self: *Struct,
        name: []const u8,
        options: ContainerOptions,
    ) Error!Tuple {
        try self.fieldPrefix(name);
        return self.container.serializer.beginTuple(options);
    }

    /// Print a field prefix. This prints any necessary commas, the field name (escaped if
    /// necessary) and whitespace as configured. Useful if you want to serialize the field
    /// value yourself.
    pub fn fieldPrefix(self: *Struct, name: []const u8) Error!void {
        try self.container.fieldPrefix(name);
    }
};

const Container = struct {
    const FieldStyle = enum { named, anon };

    serializer: *Serializer,
    field_style: FieldStyle,
    options: ContainerOptions,
    empty: bool,

    fn begin(
        sz: *Serializer,
        field_style: FieldStyle,
        options: ContainerOptions,
    ) Error!Container {
        if (options.shouldWrap()) sz.indent_level +|= 1;
        try sz.writer.writeAll(".{");
        return .{
            .serializer = sz,
            .field_style = field_style,
            .options = options,
            .empty = true,
        };
    }

    fn end(self: *Container) Error!void {
        if (self.options.shouldWrap()) self.serializer.indent_level -|= 1;
        if (!self.empty) {
            if (self.options.shouldWrap()) {
                if (self.serializer.options.whitespace) {
                    try self.serializer.writer.writeByte(',');
                }
                try self.serializer.newline();
                try self.serializer.indent();
            } else if (!self.shouldElideSpaces()) {
                try self.serializer.space();
            }
        }
        try self.serializer.writer.writeByte('}');
        self.* = undefined;
    }

    fn fieldPrefix(self: *Container, name: ?[]const u8) Error!void {
        if (!self.empty) {
            try self.serializer.writer.writeByte(',');
        }
        self.empty = false;
        if (self.options.shouldWrap()) {
            try self.serializer.newline();
        } else if (!self.shouldElideSpaces()) {
            try self.serializer.space();
        }
        if (self.options.shouldWrap()) try self.serializer.indent();
        if (name) |n| {
            try self.serializer.ident(n);
            try self.serializer.space();
            try self.serializer.writer.writeByte('=');
            try self.serializer.space();
        }
    }

    fn field(
        self: *Container,
        name: ?[]const u8,
        val: anytype,
        options: ValueOptions,
    ) Error!void {
        comptime assert(!typeIsRecursive(@TypeOf(val)));
        try self.fieldArbitraryDepth(name, val, options);
    }

    /// Returns `error.ExceededMaxDepth` if `depth` is exceeded.
    fn fieldMaxDepth(
        self: *Container,
        name: ?[]const u8,
        val: anytype,
        options: ValueOptions,
        depth: usize,
    ) DepthError!void {
        try checkValueDepth(val, depth);
        try self.fieldArbitraryDepth(name, val, options);
    }

    fn fieldArbitraryDepth(
        self: *Container,
        name: ?[]const u8,
        val: anytype,
        options: ValueOptions,
    ) Error!void {
        try self.fieldPrefix(name);
        try self.serializer.valueArbitraryDepth(val, options);
    }

    fn shouldElideSpaces(self: *const Container) bool {
        return switch (self.options.whitespace_style) {
            .fields => |fields| self.field_style != .named and fields == 1,
            else => false,
        };
    }
};

test Serializer {
    var discarding: Writer.Discarding = .init(&.{});
    var s: Serializer = .{ .writer = &discarding.writer };
    var vec2 = try s.beginStruct(.{});
    try vec2.field("x", 1.5, .{});
    try vec2.fieldPrefix("prefix");
    try s.value(2.5, .{});
    try vec2.end();
}

inline fn typeIsRecursive(comptime T: type) bool {
    return comptime typeIsRecursiveInner(T, &.{});
}

fn typeIsRecursiveInner(comptime T: type, comptime prev_visited: []const type) bool {
    for (prev_visited) |V| {
        if (V == T) return true;
    }
    const visited = prev_visited ++ .{T};

    return switch (@typeInfo(T)) {
        .pointer => |pointer| typeIsRecursiveInner(pointer.child, visited),
        .optional => |optional| typeIsRecursiveInner(optional.child, visited),
        .array => |array| typeIsRecursiveInner(array.child, visited),
        .vector => |vector| typeIsRecursiveInner(vector.child, visited),
        .@"struct" => |@"struct"| for (@"struct".fields) |field| {
            if (typeIsRecursiveInner(field.type, visited)) break true;
        } else false,
        .@"union" => |@"union"| inline for (@"union".fields) |field| {
            if (typeIsRecursiveInner(field.type, visited)) break true;
        } else false,
        else => false,
    };
}

test typeIsRecursive {
    try std.testing.expect(!typeIsRecursive(bool));
    try std.testing.expect(!typeIsRecursive(struct { x: i32, y: i32 }));
    try std.testing.expect(!typeIsRecursive(struct { i32, i32 }));
    try std.testing.expect(typeIsRecursive(struct { x: i32, y: i32, z: *@This() }));
    try std.testing.expect(typeIsRecursive(struct {
        a: struct {
            const A = @This();
            b: struct {
                c: *struct {
                    a: ?A,
                },
            },
        },
    }));
    try std.testing.expect(typeIsRecursive(struct {
        a: [3]*@This(),
    }));
    try std.testing.expect(typeIsRecursive(struct {
        a: union { a: i32, b: *@This() },
    }));
}

fn checkValueDepth(val: anytype, depth: usize) error{ExceededMaxDepth}!void {
    if (depth == 0) return error.ExceededMaxDepth;
    const child_depth = depth - 1;

    switch (@typeInfo(@TypeOf(val))) {
        .pointer => |pointer| switch (pointer.size) {
            .one => try checkValueDepth(val.*, child_depth),
            .slice => for (val) |item| {
                try checkValueDepth(item, child_depth);
            },
            .c, .many => {},
        },
        .array => for (val) |item| {
            try checkValueDepth(item, child_depth);
        },
        .@"struct" => |@"struct"| inline for (@"struct".fields) |field_info| {
            try checkValueDepth(@field(val, field_info.name), child_depth);
        },
        .@"union" => |@"union"| if (@"union".tag_type == null) {
            return;
        } else switch (val) {
            inline else => |payload| {
                return checkValueDepth(payload, child_depth);
            },
        },
        .optional => if (val) |inner| try checkValueDepth(inner, child_depth),
        else => {},
    }
}

fn expectValueDepthEquals(expected: usize, v: anytype) !void {
    try checkValueDepth(v, expected);
    try std.testing.expectError(error.ExceededMaxDepth, checkValueDepth(v, expected - 1));
}

test checkValueDepth {
    try expectValueDepthEquals(1, 10);
    try expectValueDepthEquals(2, .{ .x = 1, .y = 2 });
    try expectValueDepthEquals(2, .{ 1, 2 });
    try expectValueDepthEquals(3, .{ 1, .{ 2, 3 } });
    try expectValueDepthEquals(3, .{ .{ 1, 2 }, 3 });
    try expectValueDepthEquals(3, .{ .x = 0, .y = 1, .z = .{ .x = 3 } });
    try expectValueDepthEquals(3, .{ .x = 0, .y = .{ .x = 1 }, .z = 2 });
    try expectValueDepthEquals(3, .{ .x = .{ .x = 0 }, .y = 1, .z = 2 });
    try expectValueDepthEquals(2, @as(?u32, 1));
    try expectValueDepthEquals(1, @as(?u32, null));
    try expectValueDepthEquals(1, null);
    try expectValueDepthEquals(2, &1);
    try expectValueDepthEquals(3, &@as(?u32, 1));

    const Union = union(enum) {
        x: u32,
        y: struct { x: u32 },
    };
    try expectValueDepthEquals(2, Union{ .x = 1 });
    try expectValueDepthEquals(3, Union{ .y = .{ .x = 1 } });

    const Recurse = struct { r: ?*const @This() };
    try expectValueDepthEquals(2, Recurse{ .r = null });
    try expectValueDepthEquals(5, Recurse{ .r = &Recurse{ .r = null } });
    try expectValueDepthEquals(8, Recurse{ .r = &Recurse{ .r = &Recurse{ .r = null } } });

    try expectValueDepthEquals(2, @as([]const u8, &.{ 1, 2, 3 }));
    try expectValueDepthEquals(3, @as([]const []const u8, &.{&.{ 1, 2, 3 }}));
}

inline fn canSerializeType(T: type) bool {
    comptime return canSerializeTypeInner(T, &.{}, false);
}

fn canSerializeTypeInner(
    T: type,
    /// Visited structs and unions, to avoid infinite recursion.
    /// Tracking more types is unnecessary, and a little complex due to optional nesting.
    visited: []const type,
    parent_is_optional: bool,
) bool {
    return switch (@typeInfo(T)) {
        .bool,
        .int,
        .float,
        .comptime_float,
        .comptime_int,
        .null,
        .enum_literal,
        => true,

        .noreturn,
        .void,
        .type,
        .undefined,
        .error_union,
        .error_set,
        .@"fn",
        .frame,
        .@"anyframe",
        .@"opaque",
        => false,

        .@"enum" => |@"enum"| @"enum".is_exhaustive,

        .pointer => |pointer| switch (pointer.size) {
            .one => canSerializeTypeInner(pointer.child, visited, parent_is_optional),
            .slice => canSerializeTypeInner(pointer.child, visited, false),
            .many, .c => false,
        },

        .optional => |optional| if (parent_is_optional)
            false
        else
            canSerializeTypeInner(optional.child, visited, true),

        .array => |array| canSerializeTypeInner(array.child, visited, false),
        .vector => |vector| canSerializeTypeInner(vector.child, visited, false),

        .@"struct" => |@"struct"| {
            for (visited) |V| if (T == V) return true;
            const new_visited = visited ++ .{T};
            for (@"struct".fields) |field| {
                if (!canSerializeTypeInner(field.type, new_visited, false)) return false;
            }
            return true;
        },
        .@"union" => |@"union"| {
            for (visited) |V| if (T == V) return true;
            const new_visited = visited ++ .{T};
            if (@"union".tag_type == null) return false;
            for (@"union".fields) |field| {
                if (field.type != void and !canSerializeTypeInner(field.type, new_visited, false)) {
                    return false;
                }
            }
            return true;
        },
    };
}

test canSerializeType {
    try std.testing.expect(!comptime canSerializeType(void));
    try std.testing.expect(!comptime canSerializeType(struct { f: [*]u8 }));
    try std.testing.expect(!comptime canSerializeType(struct { error{foo} }));
    try std.testing.expect(!comptime canSerializeType(union(enum) { a: void, f: [*c]u8 }));
    try std.testing.expect(!comptime canSerializeType(@Vector(0, [*c]u8)));
    try std.testing.expect(!comptime canSerializeType(*?[*c]u8));
    try std.testing.expect(!comptime canSerializeType(enum(u8) { _ }));
    try std.testing.expect(!comptime canSerializeType(union { foo: void }));
    try std.testing.expect(comptime canSerializeType(union(enum) { foo: void }));
    try std.testing.expect(comptime canSerializeType(comptime_float));
    try std.testing.expect(comptime canSerializeType(comptime_int));
    try std.testing.expect(!comptime canSerializeType(struct { comptime foo: ??u8 = null }));
    try std.testing.expect(comptime canSerializeType(@TypeOf(.foo)));
    try std.testing.expect(comptime canSerializeType(?u8));
    try std.testing.expect(comptime canSerializeType(*?*u8));
    try std.testing.expect(comptime canSerializeType(?struct {
        foo: ?struct {
            ?union(enum) {
                a: ?@Vector(0, ?*u8),
            },
            ?struct {
                f: ?[]?u8,
            },
        },
    }));
    try std.testing.expect(!comptime canSerializeType(??u8));
    try std.testing.expect(!comptime canSerializeType(?*?u8));
    try std.testing.expect(!comptime canSerializeType(*?*?*u8));
    try std.testing.expect(comptime canSerializeType(struct { x: comptime_int = 2 }));
    try std.testing.expect(comptime canSerializeType(struct { x: comptime_float = 2 }));
    try std.testing.expect(comptime canSerializeType(struct { comptime_int }));
    try std.testing.expect(comptime canSerializeType(struct { comptime x: @TypeOf(.foo) = .foo }));
    const Recursive = struct { foo: ?*@This() };
    try std.testing.expect(comptime canSerializeType(Recursive));

    // Make sure we validate nested optional before we early out due to already having seen
    // a type recursion!
    try std.testing.expect(!comptime canSerializeType(struct {
        add_to_visited: ?u8,
        retrieve_from_visited: ??u8,
    }));
}  