#74 dupe() methods fail to compile (#75)

* reproducing the issue

* dupe can only make allocator errors, and this was hard to handle for the compiler.

src/protobuf.zig

@@ -501,7 +501,7 @@ pub fn pb_dupe(comptime T: type, original: T, allocator: Allocator) !T {
 }
 
 /// Internal dupe function for a specific field
-fn dupe_field(original: anytype, comptime field_name: []const u8, comptime ftype: FieldType, allocator: Allocator) !@TypeOf(@field(original, field_name)) {
+fn dupe_field(original: anytype, comptime field_name: []const u8, comptime ftype: FieldType, allocator: Allocator) Allocator.Error!@TypeOf(@field(original, field_name)) {
     switch (ftype) {
         .Varint, .FixedInt => {
             return @field(original, field_name);

tests/generated/opentelemetry/proto/common/v1.pb.zig

@@ -0,0 +1,95 @@
+// Code generated by protoc-gen-zig
+///! package opentelemetry.proto.common.v1
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+const ArrayList = std.ArrayList;
+
+const protobuf = @import("protobuf");
+const ManagedString = protobuf.ManagedString;
+const fd = protobuf.fd;
+
+pub const AnyValue = struct {
+    value: ?value_union,
+
+    pub const _value_case = enum {
+        string_value,
+        bool_value,
+        int_value,
+        double_value,
+        array_value,
+        kvlist_value,
+        bytes_value,
+    };
+    pub const value_union = union(_value_case) {
+        string_value: ManagedString,
+        bool_value: bool,
+        int_value: i64,
+        double_value: f64,
+        array_value: ArrayValue,
+        kvlist_value: KeyValueList,
+        bytes_value: ManagedString,
+        pub const _union_desc = .{
+            .string_value = fd(1, .String),
+            .bool_value = fd(2, .{ .Varint = .Simple }),
+            .int_value = fd(3, .{ .Varint = .Simple }),
+            .double_value = fd(4, .{ .FixedInt = .I64 }),
+            .array_value = fd(5, .{ .SubMessage = {} }),
+            .kvlist_value = fd(6, .{ .SubMessage = {} }),
+            .bytes_value = fd(7, .Bytes),
+        };
+    };
+
+    pub const _desc_table = .{
+        .value = fd(null, .{ .OneOf = value_union }),
+    };
+
+    pub usingnamespace protobuf.MessageMixins(@This());
+};
+
+pub const ArrayValue = struct {
+    values: ArrayList(AnyValue),
+
+    pub const _desc_table = .{
+        .values = fd(1, .{ .List = .{ .SubMessage = {} } }),
+    };
+
+    pub usingnamespace protobuf.MessageMixins(@This());
+};
+
+pub const KeyValueList = struct {
+    values: ArrayList(KeyValue),
+
+    pub const _desc_table = .{
+        .values = fd(1, .{ .List = .{ .SubMessage = {} } }),
+    };
+
+    pub usingnamespace protobuf.MessageMixins(@This());
+};
+
+pub const KeyValue = struct {
+    key: ManagedString = .Empty,
+    value: ?AnyValue = null,
+
+    pub const _desc_table = .{
+        .key = fd(1, .String),
+        .value = fd(2, .{ .SubMessage = {} }),
+    };
+
+    pub usingnamespace protobuf.MessageMixins(@This());
+};
+
+pub const InstrumentationScope = struct {
+    name: ManagedString = .Empty,
+    version: ManagedString = .Empty,
+    attributes: ArrayList(KeyValue),
+    dropped_attributes_count: u32 = 0,
+
+    pub const _desc_table = .{
+        .name = fd(1, .String),
+        .version = fd(2, .String),
+        .attributes = fd(3, .{ .List = .{ .SubMessage = {} } }),
+        .dropped_attributes_count = fd(4, .{ .Varint = .Simple }),
+    };
+
+    pub usingnamespace protobuf.MessageMixins(@This());
+};