From 21a9753d46ceeb37bd1c8cb08ec8d3cf652eade6 Mon Sep 17 00:00:00 2001
From: torque <torque@epicyclic.dev>
Date: Thu, 23 Nov 2023 17:47:21 -0800
Subject: [PATCH] parser: change omitted value behavior to work with all
 default values

Special casing optional values was a little odd before. Now, the user
can supply a default value for any field that may be omitted from the
serialized data. This behaves the same way as the stdlib JSON parser
as well.
---
 src/parser.zig       | 10 +++++-----
 src/parser/value.zig | 14 ++++++++++----
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/parser.zig b/src/parser.zig
index 3fc7524..c697fef 100644
--- a/src/parser.zig
+++ b/src/parser.zig
@@ -61,11 +61,11 @@ pub const Options = struct {
     ignore_extra_fields: bool = true,
 
     // Only used by the parseTo family of functions.
-    // If true, if a struct field is an optional type and the corresponding mapping key
-    // does not exist, the object field will be set to `null`. By default, if the
-    // parsed document is missing a mapping key for a given field, an error will be
-    // raised instead.
-    treat_omitted_as_null: bool = false,
+    // If true, if a struct field has a default value associated with it and the
+    // corresponding mapping key does not exist, the object field will be set to the
+    // default value. By default, this behavior is enabled, allowing succinct
+    // representation of objects that have default fields.
+    allow_omitting_default_values: bool = true,
 
     // Only used by the parseTo family of functions.
     // If true, strings may be coerced into other scalar types, like booleans or
diff --git a/src/parser/value.zig b/src/parser/value.zig
index 0d27ffc..1503a8e 100644
--- a/src/parser/value.zig
+++ b/src/parser/value.zig
@@ -208,8 +208,11 @@ pub const Value = union(enum) {
                             inline for (stt.fields) |field| {
                                 if (map.get(field.name)) |value| {
                                     @field(result, field.name) = try value.convertTo(field.type, allocator, options);
-                                } else if (options.treat_omitted_as_null and @typeInfo(field.type) == .Optional) {
-                                    @field(result, field.name) = null;
+                                } else if (options.allow_omitting_default_values) {
+                                    if (comptime field.default_value) |def|
+                                        @field(result, field.name) = @as(*align(1) const field.type, @ptrCast(def)).*
+                                    else
+                                        return error.BadValue;
                                 } else {
                                     return error.BadValue;
                                 }
@@ -224,8 +227,11 @@ pub const Value = union(enum) {
                             inline for (stt.fields) |field| {
                                 if (clone.fetchSwapRemove(field.name)) |kv| {
                                     @field(result, field.name) = try kv.value.convertTo(field.type, allocator, options);
-                                } else if (options.treat_omitted_as_null and @typeInfo(field.type) == .Optional) {
-                                    @field(result, field.name) = null;
+                                } else if (options.allow_omitting_default_values) {
+                                    if (comptime field.default_value) |def|
+                                        @field(result, field.name) = @as(*align(1) const field.type, @ptrCast(def)).*
+                                    else
+                                        return error.BadValue;
                                 } else return error.BadValue;
                             }
                             // there were extra fields in the data